~2022~

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

         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.

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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, https://doi.org/10.1021/acsenergylett.1c02631

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.

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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, https://onlinelibrary.wiley.com/doi/full/10.1002/adfm.202112126

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.

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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, https://www.sciencedirect.com/science/article/pii/S2542435121005730

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.

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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, https://www.sciencedirect.com/science/article/pii/S2666386422000285

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.

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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
         Chueh

        ACS Applied Materials & Interfaces,  2022, https://pubs.acs.org/doi/abs/10.1021/acsami.1c23594

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.

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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, https://doi.org/10.1002/idm2.12023

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.

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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, https://doi.org/10.1039/D2EE00977C

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.

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256. "Development and challenges of metal halide perovskite solar modules"
         Yuanhang Cheng, Yong Peng, Alex K-Y Jen, Hin-Lap Yip
        Solar RRL,  2022,  https://doi.org/10.1002/solr.202100545

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.

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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, https://doi.org/10.48550/arXiv.2203.09990

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.

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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, https://doi.org/10.1016/j.jechem.2022.03.019

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.

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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, https://doi.org/10.1002/aenm.202102973

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.

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