top of page


248. "Stepwise on-surface synthesis of thiophene-based polymeric ribbons by coupling reactions and the carbon–fluorine bond       

         Liqian Liu, Hengqi Zou, Xinrui Miao, Hin-Lap Yip, Wenli Deng, Yong Cao
        Physical Chemistry Chemical Physics,  2022, DOI: 10.1039/D1CP04039A 

The rational synthesis of thiophene-based cross-coupled polymers on surfaces has been attracting more attention recently. Here, we report the stepwise activation of 5,5′-(2,3-difluoro-1,4-phenylene)bis(2-bromothiophene) as a precursor to synthesize thiophene-based polymeric ribbons on the Au(111) surface. Scanning tunneling microscopy studies showed that the precursor adopted different conformations in the self-assembled structure, organometallic species, and covalent polymers. On annealing the sample at a relatively low temperature (150 °C), the conversion of the organometallic structure into a covalent product with straight lines was observed, in which the Br adatoms arranged between the neighboring chains. On further annealing the sample at 270 °C, the detached Br adatoms played a key role in promoting the C–H bond activation. The cross-linked polymer was achieved by a combination of Ullmann and dehydrogenative coupling. When the annealing temperature was up to 390 °C, the C–F bond activation was triggered, which led to the formation of polymeric ribbons resulting from the cyclodehydrogenation of the fluorinated polymer. This study further supplements the reaction mechanism of thiophene-based dehalogenative, dehydrogenative and defluorinative coupling, and provides us a rational way for synthesizing cross-linked functional materials.


249. "Perovskite/Organic Hybrid White Electroluminescent Devices with Stable Spectrum and Extended Operating Lifetime"
         Denghui Liu, Xinyan Liu, Yiyang Gan, Zhe Liu, Guanwei Sun, Chenyang Shen, Xiaomei Peng, Weidong Qiu, Deli Li,
         Zhisheng Zhou, Zhenchao Li, Hin-Lap Yip, Shi-Jian Su

        ACS Energy Letters,  2022,

We demonstrate a kind of perovskite/organic hybrid white electroluminescent device, where an ultrathin doping-free organic phosphorescent interlayer is embedded between a p-type hole transport layer and a n-type electron transport layer to give an organic p–i–n heterojunction unit, which is superimposed layer by layer onto a quasi-two-dimensional perovskite layer. The unique carrier transport character of the p-type hole transport layer leads to a broad carrier recombination region approaching the p–i–n heterojunction unit. As a result, pure-red emission from the perovskite layer and sky-blue emission from the organic p–i–n heterojunction were simultaneously achieved to generate white emission with a peak external quantum efficiency of 7.35%, Commission Internationale de L’Eclairage coordinates of (0.424, 0.363), and a low correlated color temperature of 2868 K. More importantly, excellent spectral stability and a greatly enhanced operating lifetime (10-fold longer than those of perovskite-only LEDs) are simultaneously achieved, providing a new path for the development of high-performance white LEDs.


250. "Homogeneous Grain Boundary Passivation in Wide‐Bandgap Perovskite Films Enables Fabrication of Monolithic
         Perovskite/Organic Tandem Solar Cells with over 21% Efficiency"

         Yue‐Min Xie, Qin Yao, Zixin Zeng, Qifan Xue, Tianqi Niu, Ruoxi Xia, Yuanhang Cheng, Francis Lin, Sai‐Wing Tsang, Alex K‐Y 
         Jen, Hin‐Lap Yip, Yong Cao

        Advanced Functional Materials,  2022,

Monolithic perovskite/organic tandem solar cells have attracted increasing attention due to their potential of being highly efficient while compatible to facile solution fabrication processes. One of the limiting factors for improving the performance of perovskite/organic tandem cells is the lack of wide-bandgap perovskites with suitable bandgap, film quality, and optoelectronic properties for front cells. In addition, the development of low-bandgap organic bulk-heterojunction (BHJ) rare cells with extended absorption in the infrared range is also critical for improving tandem cells. This work has carefully optimized mixed halide wide-bandgap perovskite (MWP) films by introducing a small amount of formamidinium (FA+) cations into the basic composition of MA1.06PbI2Br(SCN)0.12, which provides an effective means to modulate the crystallization properties and phase stability of the films. At optimized conditions, the MA0.96FA0.1PbI2Br(SCN)0.12 forms high-quality films with grain boundaries homogeneously passivated by PbI2, leading to a reduction in defect states and an enhancement in phase stability, enabling the fabrication of perovskite solar cells with a power conversion efficiency(PCE) of 17.4%. By further integrating the MWP front cell with an organic BHJ (PM6:CH1007) rare cell composed of a nonfullerene acceptor with absorption extended to 950 nm, a tandem cell with PCE over 21% is achieved.


251. "Consensus statement: Standardized reporting of power-producing luminescent solar concentrator performance"
         Chenchen Yang, Harry A Atwater, Marc A Baldo, Derya Baran, Christopher J Barile, Miles C Barr, Matthew Bates,
         Moungi G, Bawendi, Matthew R Bergren, Babak Borhan, Christoph J Brabec, Sergio Brovelli, Vladimir Bulović,
         Paola Ceroni, Michael G, Debije, Jose-Maria Delgado-Sanchez, Wen-Ji Dong, Phillip M Duxbury, Rachel C Evans,
         Stephen R Forrest, Daniel R Gamelin, Noel C Giebink, Xiao Gong, Gianmarco Griffini, Fei Guo, Christopher K Herrera,
         Anita WY Ho-Baillie, Russell J, Holmes, Sung-Kyu Hong, Thomas Kirchartz, Benjamin G Levine, Hongbo Li, Yilin Li, Dianyi
         Liu, Maria A Loi, Christine K Luscombe, Nikolay S Makarov, Fahad Mateen, Raffaello Mazzaro, Hunter McDaniel, Michael D             McGehee, Francesco Meinardi, Amador Menéndez-Velázquez, Jie Min, David B Mitzi, Mehdi Moemeni, Jun Hyuk Moon,                   Andrew Nattestad, Mohammad K Nazeeruddin, Ana F Nogueira, Ulrich W Paetzold, David L Patrick, Andrea Pucci, Barry P               Rand, Elsa Reichmanis, Bryce S Richards, Jean Roncali, Federico Rosei, Timothy W Schmidt, Franky So, Chang-Ching Tu,             Aria Vahdani, Wilfried GJHM van Sark, Rafael Verduzco, Alberto Vomiero, Wallace WH Wong, Kaifeng Wu, Hin-Lap Yip,                     Xiaowei Zhan, Haiguang Zhao, Richard R Lunt

        Joule,  2022,

Fair and meaningful device performance comparison among luminescent solar concentrator-photovoltaic (LSC-PV) reports cannot be realized without a general consensus on reporting standards in LSC-PV research. Therefore, it is imperative to adopt standardized characterization protocols for these emerging types of PV devices that are consistent with other PV devices. This commentary highlights several common limitations in LSC literature and summarizes the best practices moving forward to harmonize with standard PV reporting, considering the greater nuances present with LSC-PV. Based on these practices, a checklist of actionable items is provided to help standardize the characterization/reporting protocols and offer a set of baseline expectations for authors, reviewers, and editors. The general consensus combined with the checklist will ultimately guide LSC-PV research towards reliable and meaningful advances.


252. "Enabling high-performance, centimeter-scale organic solar cells through three-dimensional charge transportmance"
        Baobing Fan, Wenkai Zhong, Jinxiang Chen, Francis Lin, Yue Wu, Qunping Fan, Hin-Lap Yip, Alex K-Y Jen
        Cell Reports Physical Science,  2022,

Organic solar cells (OSCs) suffer from severe upscaling loss due to the inevitable formation of inhomogeneities and the intrinsically low charge mobilities of organic materials limiting the charge extraction efficiency, especially in the situation where cell width reaches centimeter scale. Here, we report the introduction of a nematic liquid crystal donor, BTR-Cl, into a typical non-fullerene blending system of PM6:BTP-eC9. The participation of BTR-Cl contributes to a significantly improved crystallinity and ordering of the host components and facilitates efficient three-dimensional charge transport in the active layer. Simultaneously improved fill factor and current density are thus achieved in BTR-Cl-doped OSCs, corresponding to a superior efficiency of 18.31%. More importantly, a high efficiency of 16.88% along with a robust fill factor of 73.4% is retained when enlarging the effective device area from 0.034 to 1.01 cm2, highlighting the importance of three-dimensional charge transport in reducing the upscaling loss of OSCs.


253. "Enhancing the Performance of Quasi-2D Perovskite Light-Emitting Diodes Using Natural Cyclic Molecules with Distinct
         Phase Regulation Behaviors"

         Chiung-Han Chen, Yen-Hung Kuo, Yu-Kuan Lin, I-Chih Ni, Bi-Hsuan Lin, Chih-I Wu, Hin-Lap Yip, Chi-Ching Kuo, Chu-Chen

        ACS Applied Materials & Interfaces,  2022,

In this study, two natural small molecules, α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD), are used as additives to improve the performance of quasi-2D PEA2Csn–1PbnBr3n+1 (n = 3, herein) PeLEDs. Both of them are shown to efficiently passivate the quasi-2D perovskite films to afford improved film quality and morphology, but they exhibit distinct phase regulation behaviors possibly due to their different pore sizes. It reveals that α-CD effectively suppresses the formation of the low-n phases (n ≤ 2), while β-CD better regulates the phase with a medium-n value (n = 3). Because of effectively suppressing the formation of low-n phases, the CD-assisted quasi-2D perovskite films possess facilitated exciton energy transfer and reduced nonradiative recombination. Consequently, the optimized α-CD-derived PeLED shows the highest luminance (Lmax) of 37,825 cd/m2 with an external quantum efficiency (EQE) of 3.81%, while the β-CD-derived PeLED delivers a lower Lmax of 24,793 cd/m2 with an EQE of 3.09%. Compared to the pristine device, Lmax is enhanced by 6.3 and 3.8 times for α-CD- and β-CD-based PeLEDs, respectively, and EQE is enhanced by ∼4.8 times for both devices; besides, both CD-assisted devices also exhibit improved color purity and a lower bias dependency of electroluminescent intensity.


254. "Subtle side chain modification of triphenylamine‐based polymer hole‐transport layer materials produces efficient and stable             inverted perovskite solar cells"
         Yue‐Min Xie, Qin Yao, Qifan Xue, Zixin Zeng, Tianqi Niu, Yingzhi Zhou, Ming‐Peng Zhuo, Sai‐Wing Tsang, Hin‐Lap Yip,
         Yong Cao

        Interdisciplinary Materials,  2022,

Polymer hole-transport layers (HTLs) are critical components of inverted perovskite solar cells (IPVSCs). Triphenylamine derivatives PTAA (poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]) and Poly-TPD (poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine]) have been widely adopted as hole-transport materials due to their perovskite passivation effects and suitable energy levels. However, the passivation mechanism (i.e., the functional group responsible for perovskite passivation) of triphenylamine derivative polymers remains unclear, hindering the development and application of this polymer type. Here, we develop a novel Poly-TPD derivative, S-Poly-TPD, by replacing the n-butyl functional group of Poly-TPD with an isobutyl group to explore the influence of alkyl groups on HTL performance and top-deposited perovskite properties. Compared with Poly-TPD, the increased CH3-terminal unit density and the decreased spatial distance between the –CH–CH3 and –CH2–CH3 units and the benzene ring in S-Poly-TPD not only enhanced the hole-transport ability but also improved the perovskite passivation effect, revealing for the first time the role of the alkyl groups in perovskite passivation. As a result, the S-Poly-TPD-based IPVSCs demonstrated high power-conversion efficiencies of 15.1% and 21.3% in wide-bandgap [MAPbI2Br(SCN)0.12] and normal-bandgap [(FAPbI3)0.92(MAPbBr3)0.08] devices, respectively.


255. "High-Performance See-Through Power Windows"
         Di Wang, Yuhao Li, Guanqing Zhou, Emely Gu, Ruoxi Xia, Buyi Yan, Jizhong Yao, Haiming Zhu, Xinhui Lu, Hin-Lap Yip,                     Hongzheng Chen, Chang-Zhi Li
        Energy & Environmental Science,  2022,

See-through power windows are developed herein via the new design of semitransparent organic solar cells (ST-OSCs), which allow efficiently utilizing the spectra-engineered solar photons from visible to infrared range with both energy generation and saving features. These OSC-derived power windows simultaneously possess high color fidelity of visible transparency, outstanding power conversion efficiency (PCE), and energy-saving from the excellent infrared photon rejection. Further, large-area modules were demonstrated with record PCEs of 16.04% (certified as 15.46%) in opaque and 11.28% for see-through ones, representing the best-performed organic solar minimodules to date. These modules have worked healthily under outdoor operation. Our model analysis indicated the installment of these see-through power windows worldwide would allow making certain contributions to the carbon neutrality of society.


256. "Development and challenges of metal halide perovskite solar modules"
         Yuanhang Cheng, Yong Peng, Alex K-Y Jen, Hin-Lap Yip
        Solar RRL,  2022,

Metal halide perovskites are considered as game changers for future solar cell technology due to their rapidly increasing device efficiencies and potential for manufacturing at low cost. In view of their promising commercial potential, increasing research efforts are now dedicated to the development of large-area perovskite solar modules. Herein, the motivation for developing perovskite solar modules and the challenges to fabricate large-area perovskite solar cells with high efficiency are discussed. The important thin-film processing methods including solution-based and vacuum-based deposition technologies for scaling up the fabrication of perovskites are reviewed. In addition, other key challenges that need to be overcome to bring perovskite solar modules into photovoltaic (PV) markets are also discussed, including module stability, potential lead leakage issue, and outdoor field testing of the perovskite modules. Finally, opinions on the future development of perovskite PV modules are shared.


257. "Identifying structure-absorption relationships and predicting absorption strength of non-fullerene acceptors for organic                       photovoltaics"
         Jun Yan, Xabier Rodriguez-Martinez, Drew Pearce, Hana Douglas, Danai Bili, Mohammed Azzouzi, Flurin Eisner, Alise                     Virbule, Elham Rezasoltani, Valentina Belova, Bernhard Dorling, Sheridan Few, Anna A Szumska, Xueyan Hou, Guichuan                 Zhang, Hin-Lap Yip, Mariano Campoy-Quiles, Jenny Nelson
        arXiv preprint arXiv,  2022,

Non-fullerene acceptors (NFAs) are excellent light harvesters, yet the origin of such high optical extinction is not well understood. In this work, we investigate the absorption strength of NFAs by building a database of time-dependent density functional theory (TDDFT) calculations of ~500 pi-conjugated molecules. The calculations are first validated by comparison with experimental measurements on liquid and solid state using common fullerene and non-fullerene acceptors. We find that the molar extinction coefficient ({\epsilon}_(d,max)) shows reasonable agreement between calculation in vacuum and experiment for molecules in solution, highlighting the effectiveness of TDDFT for predicting optical properties of organic pi-conjugated molecules. We then perform a statistical analysis based on molecular descriptors to identify which features are important in defining the absorption strength. This allows us to identify structural features that are correlated with high absorption strength in NFAs and could be used to guide molecular design: highly absorbing NFAs should possess a planar, linear, and fully conjugated molecular backbone with highly polarisable heteroatoms. We then exploit a random decision forest to draw predictions for {\epsilon}_(d,max) using a computational framework based on extended tight-binding Hamiltonians, which shows reasonable predicting accuracy with lower computational cost than TDDFT. This work provides a general understanding of the relationship between molecular structure and absorption strength in pi-conjugated organic molecules, including NFAs, while introducing predictive machine-learning models of low computational cost.


258. "Understanding the role of interconnecting layer on determining monolithic perovskite/organic tandem device carrier                           recombination properties"
         Yue-Min Xie, Tianqi Niu, Qin Yao, Qifan Xue, Zixin Zeng, Yuanhang Cheng, Hin-Lap Yip, Yong Cao
        Journal of Energy Chemistry,  2022,

As one of the core parts of two-terminal (2T) monolithic tandem photovoltaics, the interconnecting layers (ICLs) play a critical role in modulating the carrier transport and recombination between the sub-cells, and thus influencing the tandem device performance. Here, for the first time, the relationship between ICLs architecture and 2T monolithic perovskite/organic tandem device performance has been studied by investigating the change of ICLs composition layer thickness on the ICLs optical and electrical properties, sub-cells EQE properties, and tandem device J-V properties. It is revealed that the ability of ICLs on modulating the sub-cells carrier balance properties is strongly associated with its composited layers thickness, and the tandem device carrier balance properties can be reflected by the relative EQE intensity between the sub-cells. Finally, with a deep understanding of the mechanisms, rational design of ICLs can be made to benefit the tandem device development. Based on the optimized ICL a high PCE of 20.03% is achieved.


259. "Spacer Engineering of Diammonium‐Based 2D Perovskites toward Efficient and Stable 2D/3D Heterostructure Perovskite                 Solar Cells"
         Tianqi Niu, Yue‐Min Xie, Qifan Xue, Sangni Xun, Qin Yao, Fuchao Zhen, Wenbo Yan, Hong Li, Jean‐Luc Brédas, Hin‐Lap Yip,           Yong Cao
        Advanced Energy Materials,  2022,

Perovskite solar cells (PSCs) based on 2D/3D heterostructures show great potential to combine the advantages of the high efficiency of 3D perovskites and the high stability of 2D perovskites. However, an in-depth understanding of the organic-spacer effects on the 2D quantum well (QW) structures and electronic properties at the 2D/3D interfaces is yet to be fully achieved, especially in the case of 2D perovskites based on diammonium spacers/ligands. Here, a series of diammonium spacers is considered for the construct ion 2D/3D perovskite heterostructures. It is found that the chemical structure and concentration of the spacers can dramatically affect the characteristics of the 2D capping layers, including their phase purity and orientation. Density functional theory calculations indicate that the spacer modifications can induce shifts in the energy-level alignments at the 2D/3D interfaces and therefore influence the charge-transfer characteristics. The strong intermolecular interactions between the 2,2-(ethylenedioxy)bis(ethylammonium) (EDBE) cations and inorganic [PbI6]4− slabs facilitate a controlled deposition of a phase-pure QW structure (n = 1) with a horizontal orientation, which leads to better surface passivation and carrier extraction. These benefits endow the EDBE-based 2D/3D devices with a high power conversion efficiency of 22.6% and remarkable environmental stability, highlighting the promise of spacer-chemistry design for high-performance 2D/3D PSCs.


260. "Unravelling Alkali‐Metal‐Assisted Domain Distribution of Quasi‐2D Perovskites for Cascade Energy Transfer toward Efficient             Blue Light‐Emitting Diodes"
         Wanqing Cai, Muhammad Umair Ali, Ping Liu, Miao He, Cong Zhao, Ziming Chen, Yue Zang, Man‐Chung Tang, Hong Meng,           Hongyan Fu, Guodan Wei, Hin‐Lap Yip
        Advanced Science,  2022,

Solution processable quasi-2D (Q-2D) perovskite materials are emerging as a promising candidate for blue light source in full-color display applications due to their good color saturation property, high brightness, and spectral tunability. Herein, an efficient energy cascade channel is developed by introducing sodium bromide (NaBr) in phenyl-butylammonium (PBA)-containing mixed-halide Q-2D perovskites for a blue perovskite light-emitting diode (PeLED). The incorporation of alkali metal contributes to the nucleation and growth of Q-2D perovskites into graded distribution of domains with different layer number <n>. The study of excitation dynamics by transient absorption (TA) spectroscopy confirms that NaBr induces more Q-2D perovskite phases with small n number, providing a graded energy cascade pathway to facilitate more efficient energy transfer processes. In addition, the nonradiative recombination within the Q-2D perovskites is significantly suppressed upon Na+ incorporation, as validated by the trap density estimation. Consequently, the optimized blue PeLEDs manifest a peak external quantum efficiency (EQE) of 7.0% emitting at 486 nm with a maximum luminance of 1699 cd m−2. It is anticipated that these findings will improve the understanding of alkali-metal-assisted optimization of Q-2D perovskites and pave the way toward high-performance blue PeLEDs.


261. "Perovskite‐Gallium Nitride Tandem Light‐Emitting Diodes with Improved Luminance and Color Tunability"
        Zong‐Tao Li, Hong‐Wei Zhang, Jia‐Sheng Li, Kai Cao, Ziming Chen, Liang Xu, Xin‐Rui Ding, Bin‐Hai Yu, Yong Tang, Jian‐                Zhen Ou, Hao‐Chung Kuo, Hin‐Lap Yip
        Advanced Science,  2022,

Tandem structures with different subpixels are promising for perovskite-based multicolor electroluminescence (EL) devices in ultra-high-resolution full-color displays; however, realizing excellent luminance- and color-independent tunability considering the low brightness and stability of blue perovskite light-emitting diodes (PeLEDs) remains a challenge. Herein, a bright and stable blue gallium nitride (GaN) LED is utilized for vertical integration with a green MAPbBr3 PeLED, successfully achieving a Pe-GaN tandem LED with independently tunable luminance and color. The electronic and photonic co-excitation (EPCE) effect is found to suppress the radiative recombination and current injection of PeLEDs, leading to degraded luminance and current efficiency under direct current modulation. Accordingly, the pulse-width modulation is introduced to the tandem device with a negligible EPCE effect, and the average hybrid current efficiency is significantly improved by 139.5%, finally achieving a record tunable luminance (average tuning range of 16631 cd m−2 at an arbitrary color from blue to green) for perovskite-based multi-color LEDs. The reported excellent independent tunability can be the starting point for perovskite-based multicolor EL devices, enabling the combination with matured semiconductor technologies to facilitate their commercialization in advanced display applications with ultra-high resolution.


262. "Non-Fullerene Acceptor Doped Block Copolymer for Efficient and Stable Organic Solar Cells"
        Yue Wu, Qunping Fan, Baobing Fan, Feng Qi, Ziang Wu, Francis R Lin, Yang Li, Chun-Sing Lee, Han Young Woo, Hin-Lap Yip,          Alex K-Y Jen
        ACS Energy Letters,  2022,

Bulk-heterojunction organic solar cells (OSCs) often suffer from morphological instability due to thermo- or photoinduced molecular diffusion. To circumvent such instability, OSCs incorporating a single-component block copolymer with covalently bonded blocks can restrain molecular diffusion. However, the device efficiencies of such block copolymers are lagging behind those based on a blended active layer due to a nonideal morphological problem. Herein, we successfully alleviate this problem by introducing a small-molecule additive, Y6, having a structure similar to that of the acceptor block. The addition of Y6 improves the packing of acceptor blocks in the block copolymer, PM6-b-PYIT. This helps improve electron transport and enhances the device efficiency to 15.55%, representing the highest value reported for block-copolymer-based OSCs. Moreover, the device stability is significantly improved due to the padding of Y6 into the nanovoids of the copolymer matrix to restrict the molecular motion. This work presents an effective strategy to address the efficiency–stability tradeoff in OSCs.


263. "Elucidating the Role of Antisolvents on the Surface Chemistry and Optoelectronic Properties of CsPbBrxI3-x Perovskite                   Nanocrystals"
        Junzhi Ye, Zhenchao Li, Dominik J Kubicki, Yunwei Zhang, Linjie Dai, Clara Otero-Martínez, Manuel A Reus, Rakesh Arul,                Kavya Reddy Dudipala, Zahra Andaji-Garmaroudi, Yi-Teng Huang, Zewei Li, Ziming Chen, Peter Müller-Buschbaum, Hin-Lap            Yip, Samuel D Stranks, Clare P Grey, Jeremy J Baumberg, Neil C Greenham, Lakshminarayana Polavarapu, Akshay Rao,                Robert LZ Hoye
        Journal of the American Chemical Society,  2022,

Colloidal lead-halide perovskite nanocrystals (LHP NCs) have emerged over the past decade as leading candidates for efficient next-generation optoelectronic devices, but their properties and performance critically depend on how they are purified. While antisolvents are widely used for purification, a detailed understanding of how the polarity of the antisolvent influences the surface chemistry and composition of the NCs is missing in the field. Here, we fill this knowledge gap by studying the surface chemistry of purified CsPbBrxI3-x NCs as the model system, which in itself is considered a promising candidate for pure-red light-emitting diodes and top-cells for tandem photovoltaics. Interestingly, we find that as the polarity of the antisolvent increases (from methyl acetate to acetone to butanol), there is a blueshift in the photoluminescence (PL) peak of the NCs along with a decrease in PL quantum yield (PLQY). Through transmission electron microscopy and X-ray photoemission spectroscopy measurements, we find that these changes in PL properties arise from antisolvent-induced iodide removal, which leads to a change in halide composition and, thus, the bandgap. Using detailed nuclear magnetic resonance (NMR) and Fourier-transform infrared spectroscopy (FTIR) measurements along with density functional theory calculations, we propose that more polar antisolvents favor the detachment of the oleic acid and oleylamine ligands, which undergo amide condensation reactions, leading to the removal of iodide anions from the NC surface bound to these ligands. This work shows that careful selection of low-polarity antisolvents is a critical part of designing the synthesis of NCs to achieve high PLQYs with minimal defect-mediated phase segregation.


264. "Deep‐Red Perovskite Light‐Emitting Diodes with External Quantum Efficiency Exceeding 21% Enabled by Ligand‐Modulated           Dimensionality Control"
        Zhe Liu, Xiaomei Peng, Shiyu Xing, Weidong Qiu, Mengke Li, Chao Shen, Guanwei Sun, Zhisheng Zhou, Qing Gu, Junrong              Pu, Jiaji Yang, Jibin Zhang, Denghui Liu, Chenyang Shen, Jian Qing, Qifan Xue, Hin‐Lap Yip, Dawei Di, Lintao Hou,

        Zhengjian Qi, Shi‐Jian Su
        Advanced Optical Materials,  2022,

Quasi-2D perovskites show great promise for light-emitting diodes owing to suppressed non-radiative losses enabled by the energy funneling/cascading nanostructures. However, for red emission quasi-2D perovskites, these ideal energy landscapes for efficient perovskite light-emitting diodes (PeLEDs) can rarely be achieved due to detrimental aggregation of the low-dimensional ligands in perovskite precursors, leading to poor device efficiency and stability. Here, a ligand-modulated dimensionality control strategy is explored to achieve uniform phase distribution and reduce defect density for efficient light emission. In contrast to the model phenethylammonium iodide 2D ligand, the formation of small-n phases can be inhibited by a structurally similar phenoxyethylammonium iodide ligand owing to the weakened aromatic stacking between ligands. Besides, the oxygen atoms can interact with the uncoordinated Pb2+ ions and promote the NI coordination in the perovskites, which greatly reduces the non-radiative recombination defects in the ionic lattice. With this simple and effective approach, deep-red quasi-2D PeLEDs with record-high external quantum efficiency of 21.6% and decent operational stability are achieved without the need for additional additives. These results highlight the potential of ligand-modulated dimensionality control to achieve highly efficient and stable PeLEDs with a facile fabrication process.


265. "High‐Efficiency Blue Perovskite Light‐Emitting Diodes with Improved Photoluminescence Quantum Yield via Reducing Trap‐             Induced Recombination and Exciton–Exciton Annihilation"
        Zhiqiang Guan, Yang Li, Zhaohua Zhu, Zixin Zeng, Ziming Chen, Zhiwei Ren, Gang Li, Sai‐Wing Tsang, Hin‐Lap Yip, Yuan                Xiong, Chun‐Sing Lee
        Advanced Functional Materials,  2022,

Although the performance of blue perovskite LEDs (PeLEDs) has improved rapidly in the past few years, it still lags behind their green and red counterparts. One major cause of the inferior performance is the relatively low photoluminescence quantum yield (PLQY) of blue perovskite emitters due to more severe nonradiative recombination loss induced by traps and exciton–exciton annihilation (EEA). In this study, theoretical analysis reveals that trap-induced recombination limits the maximum obtainable PLQY and EEA leads to fast roll-off at high excitons densities. To address these issues, a synergic approach by introducing CsAc into perovskite and applying solvent annealing (SA) is used to suppress the trap-induced recombination and the EEA, respectively. The acetate anion in CsAc effectively passivates defects of perovskite through Lewis acid–base reaction, enhancing PLQY of the perovskite films from 10.7% to 49.2%. Furthermore, carrier recombination dynamic investigations reveal that EEA and PLQY roll-off are successfully deferred with SA treatment. As a result, external quantum efficiency (EQE) is improved from 2.9% to 11% and EQE roll-off is significantly suppressed at high current density. This work demonstrates that alleviating trap-induced and EEA non-radiative losses are two effective methods to improve the PLQY and EQE of blue PeLEDs.


266. "Renewed Prospects for Organic Photovoltaics"
         Guichuan Zhang, Francis R Lin, Feng Qi, Thomas Heumüller, Andreas Distler, Hans-Joachim Egelhaaf, Ning Li, Philip CY                 Chow, Christoph J Brabec, Alex K-Y Jen, Hin-Lap Yip
        Chemical Reviews,  2022,

Organic photovoltaics (OPVs) have progressed steadily through three stages of photoactive materials development: (i) use of poly(3-hexylthiophene) and fullerene-based acceptors (FAs) for optimizing bulk heterojunctions; (ii) development of new donors to better match with FAs; (iii) development of non-fullerene acceptors (NFAs). The development and application of NFAs with an A–D–A configuration (where A = acceptor and D = donor) has enabled devices to have efficient charge generation and small energy losses (Eloss < 0.6 eV), resulting in substantially higher power conversion efficiencies (PCEs) than FA-based devices. The discovery of Y6-type acceptors (Y6 = 2,2′-((2Z,2′Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]-thiadiazolo[3,4-e]-thieno[2″,3″:4′,5′]thieno-[2′,3′:4,5]pyrrolo-[3,2-g]thieno-[2′,3′:4,5]thieno-[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile) with an A–DA′ D–A configuration has further propelled the PCEs to go beyond 15% due to smaller Eloss values (∼0.5 eV) and higher external quantum efficiencies. Subsequently, the PCEs of Y6-series single-junction devices have increased to >19% and may soon approach 20%. This review provides an update of recent progress of OPV in the following aspects: developments of novel NFAs and donors, understanding of the structure–property relationships and underlying mechanisms of state-of-the-art OPVs, and tasks underpinning the commercialization of OPVs, such as device stability, module development, potential applications, and high-throughput manufacturing. Finally, an outlook and prospects section summarizes the remaining challenges for the further development of OPV technology.


267. "Low-voltage-modulated perovskite/organic dual-band photodetectors for visible and near-infrared imaging"
         Yu Gao, Cong Zhao, Kai Pu, Miao He, Wanqing Cai, Man-Chung Tang, Feiyu Kang, Hin-Lap Yip, Guodan Wei
        Science Bulletin,  2022,

Visible and near-infrared (NIR) light dual-band photodetectors (PDs) have potential applications in signal detection, bioimaging, optical communications and safety monitoring. Herein, we report an ultrafast perovskite/organic heterojunction dual-mode PD with a voltage-modulated photoresponse range in visible and NIR spectra. The PD, comprising a perovskite layer to absorb visible light (500–810 nm) and an organic bulk heterojunction layer for NIR light absorption (810–950 nm), exhibited a switchable spectral response in the visible or NIR bands. The voltage-modulated visible and NIR photoresponses of the PD were attributable to controlled charge photogeneration in perovskite and organic blend thin films under different bias polarities. The device exhibited peak responsivities of 93.5 and 102.2 mA/W in the visible and NIR bands, respectively; a high detectivity of 4.3 × 109 Jones (at forward bias of 0.7 V and incident 625 nm light) and 1.6 × 1012 Jones (at reverse bias of –1.5 V and incident 900 nm light); a fast microsecond response time; and a wide dynamic range (>120 dB) both in the visible mode and NIR mode. Also, this voltage-modulated dual-band PD shows promising applications in visible light and NIR imaging, which is proven by demonstrating an PD array with 25 pixels (5×5).


268. "Molecularly Functionalized SnO2 Films by Carboxylic Acids for High-Performance Perovskite Solar Cells"
         Tianqi Niu, Fuchao Zhen, Yue-Min Xie, Tinghuan Yang, Qin Yao, Jing Lu, Kui Zhao, Hin-Lap Yip
        ACS Applied Materials & Interfaces,  2022,

Metal oxides are commonly employed as electron transport layers (ETLs) for n-i-p perovskite solar cells (PSCs), but the presence of surface traps and their mismatched energy alignment with perovskites limits the corresponding device performance. Therefore, the interfacial modification of ETLs by functional molecules becomes an important strategy for tailoring the interfacial properties and facilitating an efficient charge extraction and transport in PSCs. However, an in-depth understanding of the influences of their molecular structures on the surface chemistry and electronic properties of ETLs is rarely discussed. Herein, three carboxylic acid-based molecules with different chemical structures were employed to modify the SnO2 ETL and their effects on the performance of PSCs were systematically investigated. We found that the alkyl-chain length and carboxyl number in molecular structures can dramatically alter their binding strength to SnO2, providing a good strategy to fine-tune their film quality, electron mobility, and energy offset at the cathode interface. Benefiting from the optimal coordination ability of citric acid (CA) to SnO2, the corresponding PSCs show better charge transport properties and suppressed nonradiative recombination, leading to a champion efficiency of 23.1% with much improved environmental stability, highlighting the potential of rational design of molecular modifiers for high-performance ETLs applied in PSCs


269. "High efficiency pure blue perovskite quantum dot light-emitting diodes based on formamidinium manipulating carrier                         dynamics and electron state filling"
         Long Gao, Yilin Zhang, Lijie Gou, Qian Wang, Meng Wang, Weitao Zheng, Yinghui Wang, Hin-Lap Yip, Jiaqi Zhang
        Light: Science & Applications,  2022,

Achieving high efficiency and stable pure blue colloidal perovskite quantum dot (QD) light-emitting diodes (LEDs) is still an enormous challenge because blue emitters typically exhibit high defect density, low photoluminescence quantum yield (PLQY) and easy phase dissociation. Herein, an organic cation composition modification strategy is used to synthesize high-performance pure blue perovskite quantum dots at room temperature. The synthesized FA-CsPb(Cl0.5Br0.5)3 QDs show a bright photoluminescence with a high PLQY (65%), which is 6 times higher than the undoped samples. In addition, the photophysical properties of the FA cation doping was deeply illustrated through carrier dynamics and first principal calculation, which show lower defects, longer lifetime, and more reasonable band gap structure than undoped emitters. Consequently, pure blue FA-CsPb(Cl0.5Br0.5)3 QDs light-emitting devices were fabricated and presented a maximum luminance of 1452 cd m−2, and an external quantum efficiency of 5.01 % with an emission at 474 nm. The excellent photoelectric properties mainly originate from the enhanced blue QDs emitter and effective charge injection and exciton radiation. Our finding underscores this easy and feasible room temperature doping approach as an alternative strategy to blue perovskite QD LED development.


270. "Organic Solar Cells at Stratospheric Condition for High Altitude Platform Station Application"
         Ram Datt, Harrison Ka Hin Lee, Guichuan Zhang, Hin‐Lap Yip, Wing Chung Tsoi
        Chinese Journal of Chemistry,  2022,

High specific power or power to mass ratio is a critical concern of photovoltaic (PV) for aerospace applications. Organic solar cells (OSCs) have advantages such as high absorption coefficient, compatibility with flexible substrate, light-weight, etc. Moreover, recently OSCs achieved power conversion efficiency (PCE) over 20% with the incorporation of the non-fullerene based small molecule acceptor and high specific power is believed to be obtained. To enter the market, high-altitude platform station (HAPS) is perhaps the first place to start with. In this work, we explore and compare the in-situ performance of two high performing OSCs, using the same donor but different acceptors, in mimic HAPS environment where the pressure, temperature and the illumination conditions are controlled. We found that the use of acceptor can result in substantial difference in the performance at low temperatures.

bottom of page