Google Scholar: https://scholar.google.com/citations?hl=en&user=FJ51C38AAAAJ
215. "Long-lived and disorder-free charge transfer states enable endothermic charge separation in efficient non-fullerene organic solar cells"
Ture F Hinrichsen, Christopher CS Chan, Chao Ma, David Paleček, Alexander Gillett, Shangshang Chen, Xinhui Zou, Guichuan Zhang, Hin-Lap Yip, Kam Sing Wong, Richard H Friend, He Yan, Akshay Rao, Philip CY Chow
Nature Communications. , 2020, 11, 5617
Organic solar cells based on non-fullerene acceptors can show high charge generation yields despite near-zero donor–acceptor energy offsets to drive charge separation and overcome the mutual Coulomb attraction between electron and hole. Here, we use time-resolved optical spectroscopy to show that free charges in these systems are generated by thermally activated dissociation of interfacial charge-transfer states that occurs over hundreds of picoseconds at room temperature, three orders of magnitude slower than comparable fullerene-based systems. Upon free electron–hole encounters at later times, both charge transfer states and emissive excitons are regenerated, thus setting up an equilibrium between excitons, charge-transfer states and free charges. Our results suggest that the formation of long-lived and disorder-free charge-transfer states in these systems enables them to operate closely to quasi-thermodynamic conditions with no requirement for energy offsets to drive interfacial charge separation and achieve suppressed non-radiative recombination.
Xixiang Zhu, Guichuan Zhang, Jia Zhang, Hin-Lap Yip, Bin Hu
Joule. , 2020, https://doi.org/10.1016/j.joule.2020.09.005
Non-fullerene bulk-heterojunctions have shown an emerging driving force to realize resistance-free dissociation with energetic order toward developing high-efficiency photovoltaics. Here, by monitoring the dissociation at D:A interfaces with our magnetic field effects of photocurrent, we discovered that the self-stimulated dissociation occurs in the non-fullerene bulk-heterojunction (PM6:Y6) solar cells at the condition that the non-fullerene Y6 molecules are once optically excited to generate a photoinduced dipolar polarization. Here, the self-stimulated dissociation is a unique phenomenon to realize the resistance-free dissociation in non-fullerene organic solar cells, as against other solar cells, which lack self-stimulated dissociation mechanism. Therefore, our work provides much deeper understanding on the operating mechanism of generating photovoltaic actions to further advance non-fullerene bulk-heterojunction solar cells.
Kai Zhang, Lei Ying, Hin-Lap Yip, Fei Huang, Yong Cao
ACS Applied Materials & Interfaces. , 2020, 36, 39937-39947
Organic solar cells (OSCs) have demonstrated considerable potential in utilizing renewable solar energy because of their distinct advantages of light weight, low cost, and good flexibility. In the past decade, tremendous development in power conversion efficiency (PCE) from ∼7% to more than 17% has been witnessed. Among the various strategies of improving the PCE of OSCs, tandem structure is one of the most effective ways. In this Spotlight on Applications, we first introduce active-layer materials that we developed and selected for tandem OSC construction. We then emphasize an interconnecting layer (ICL) that we developed based on polymeric electron-transport layers. Benefiting from the organic nature of polymeric materials, the electron extraction ability and charge-transport ability of the organic electron-transport layer can be easily tuned by modifying the molecular structure or using a binary strategy, which enables us to obtain highly efficient tandem OSCs. Moreover, an ICL composed of a polymeric electron and hole-transport layer offers intrinsic advantage in obtaining a flexible tandem device and is compatible with the printing technique for fabricating large-area devices. After that, the application of the transfer matrix modeling method in predicting the best tandem OSCs architecture is introduced. Lastly, the possible research interests of tandem OSCs in the future from our point of view is discussed.
Xue Li, Ruoxi Xia, Kangrong Yan, Jie Ren, Hin-Lap Yip, Chang-Zhi Li, Hongzheng Chen
Organic solar cells (OSCs) with visible transparency and vivid colors are promising for deployment in building-integrated photovoltaics (BIPVs), yet significant challenges remain to be addressed for not only balancing the trade-off between the photovoltaic and optical properties but also controlling the bandpass of visible transmittance for the coloration of semitransparent OSCs (ST-OSCs). Herein ST-OSCs with vivid colors are successfully developed by employing one fixed active blend in the rationally designed device layout with a high-quality Fabry–Pérot electrode. With the assistance of optical simulation, vividly colorful ST-OSCs have been obtained with power conversion efficiency of >14% and maximum transmittance up to 31%. Overall, this study provides new access to OSCs with promising features as BIPVs.
Xie, Shenkun; Xia, Ruoxi; Chen, Zhen; Tian, Jingjing; Yan, Lei; Ren, Minrun; Li, Zhenchao; Zhang, Guichuan; Xue, Qifan; Yip, Hin-Lap
Nano Energy., 2020, https://doi.org/10.1016/j.nanoen.2020.105238
A high-performance monolithic perovskite/organic tandem solar cell based on the integration of a large bandgap CsPbI2Br inorganic perovskite front cell with a narrow bandgap PM6:Y6-based or PTB7-Th:O6T-4F-based bulk-heterojunction organic rear cell is demonstrated. Large bandgap inorganic perovskites are well suited candidates for the front cell due to their excellent optoelectronic properties and broad absorption for visible light, they also possess smaller voltage loss (Eloss) and higher external quantum efficiency (EQE) response when compare to their organic counterparts with approximate bandgap. Low bandgap organic solar cells offer potentially better stability and absorption tunability compared with the Sn-based perovskite counterparts, making them be good candidates for the rear cell of the tandem cells. As a result, the best power conversion efficiency (PCE) of the perovskite/organic tandem cell presented in this work reaches over 18%. In addition, based on the photovoltaic performance parameters (EQE, fill factor (FF), Eloss) that have already been achieved in state-of-the-art organic and perovskite solar cells, we further evaluate the potential PCE of the perovskite/organic tandem cells, showing a maximum calculated PCE of over 31% when the bandgaps of the subcells are optimized. This work paves the way for the development of hybrid tandem solar cells with promising performance.
210. "Delocalization of exciton and electron wavefunction in non-fullerene acceptor molecules enables efficient organic solar cells"
Zhang, Guichuan; Chen, Xian-Kai; Xiao, Jingyang; Chow, Philip CY; Ren, Minrun; Kupgan, Grit; Jiao, Xuechen; Chan, Christopher CS; Du, Xiaoyan; Xia, Ruoxi; Chen, Ziming; Yuan, Jun; Zhang, Yunqiang; Zhang, Shoufeng; Liu, Yidan; Zou, Yingping; Yan, He; Wong, Kam Sing; Coropceanu, Veaceslav, Li, Ning, Brabec, Christoph J.; Bredas, Jean-Luc; Yip, Hin-Lap; Cao, Yong
Nature Communications, 2020, 11, 3943
A major challenge for organic solar cell (OSC) research is how to minimize the tradeoff between voltage loss and charge generation. In early 2019, we reported a non-fullerene acceptor (named Y6) that can simultaneously achieve high external quantum efficiency and low voltage loss for OSC. Here, we use a combination of experimental and theoretical modeling to reveal the structure-property-performance relationships of this state-of-the-art OSC system. We find that the distinctive π–π molecular packing of Y6 not only exists in molecular single crystals but also in thin films. Importantly, such molecular packing leads to (i) the formation of delocalized and emissive excitons that enable small non-radiative voltage loss, and (ii) delocalization of electron wavefunctions at donor/acceptor interfaces that significantly reduces the Coulomb attraction between interfacial electron-hole pairs. These properties are critical in enabling highly efficient charge generation in OSC systems with negligible donor-acceptor energy offset.
Liu, Liqian; Miao, Xinrui; Shi, Tingting; Liu, Xiaogang; Yip, Hin-Lap; Deng, Wenli; Cao, Yong
Nanoscale., 2020, https://doi.org/10.1039/D0NR04529B
On-surface coupling in ultra-high vacuum is employed as a versatile approach to synthesize pure polythiophene from the 5,5''-dibromo-2,2':5',2''-terthiophene (DBTT) precursor and the corresponding temperature-dependent step-wise reaction mechanism is systematically studied by scanning tunneling microscopy (STM). After thermal deposition of the precursor onto Au(111) surface that is kept at room temperature, a triangle-like pattern and a linear self-assembled pattern are formed with different molecular coverages through Br···Br···S halogen bonds and Br···Br type-I contact bonds, respectively. In the self-assembled nanostructures, the thiophene units adopt trans-conformation. Mild annealing promotes the structural transition of both nanostructures into ordered zigzag organometallic linear chains with all-cis configured thiophene units connected through coordination bonds to the Au adatoms. Such conformational variety is easily recognized by STM, particularly in the case of DBTT-CH3 with the extra –CH3 signals. The covalently coupled products from DBTT precursor are obtained by further annealing the organometallic intermediate at higher temperatures, which lead to the removal of Au atoms and the formation of ordered polymer chains and disordered polythiophene networks. Further characterization suggests that the reaction mechanism is associated with the Ullmann-type coupling to form the ordered chains as well as the Ullmann-type and dehydrogenative C–C coupling to fabricate the cross-linked network polymer. Compared with the on-surface synthesis process of DBTT on Cu(111) surface, it can be confirmed that the Au adatoms are vital to synthesize the polythiophene. These findings provide important insight into the reaction mechanism of on-surface synthesized pure polythiophene and can potentially be applied to synthesize other functional conjugated polymers.
Yan, Lei; Li, Zhenchao; Niu, Tianqi; Xu, Xiang; Xie, Shenkun; Dong, Guanping; Xue, Qifan; Yip, Hin-Lap
Journal of Applied Physics, 2020, 128, 443102
Methylammonium (MA)-free perovskite solar cells (PVSCs) have obtained great attention recently, owing to their superior stability. However, there are still gaps in efficiency between MA-free PVSCs and MA-containing counterparts. Their stability still needs to be further enhanced for meeting commercial standards, especially the illumination stability. Here, we incorporate Zn2+ into perovskite thin films to passivate defects, successfully achieving a champion efficiency of 20.7% and reinforcing the stability of MA-free FA0.9Cs0.1PbI3 PVSCs. This study reveals that Zn-doping can increase the grain size and contribute to modulate the crystallization process. Moreover, it is found that most of the Zn2+ aggregates at the grain boundaries passivating defects and, thus, effectively restrain the non-radiative recombination in the PVSCs. These findings provide a new way of realizing highly efficient and stable PVSCs.
207. "High‐Performance Semitransparent Organic Solar Cells with Excellent Infrared Reflection and See‐Through Functions"
Wang, Di; Qin, Ran; Zhou, Guanqing; Li, Xue; Xia, Ruoxi; Li, Yuhao; Zhan, Lingling; Zhu, Haiming; Lu, Xinhui; Yip, Hin‐Lap; Chen, Hongzheng; Li, Chang-Zhi
Advanced Materials, 2020, 32, 2001621
Clean energy production and saving play vital impacts on the sustainability of the global community. Herein, high‐performance semitransparent organic solar cells (ST‐OSCs) with excellent features of power generation, being see‐through, and infrared reflection of heat dissipation, with promising perspectives for building‐integrated photovoltaics (BIPVs) are reported. To simultaneously improve average visible transmittance (AVT) and power conversion efficiency (PCE), formally in a trade‐off relationship, of ST‐OSCs, new ternary blends with alloy‐like near‐infrared (NIR) acceptors are employed, which are effective to improve device efficiency while maintaining visible absorption unchanged, resulting in PCEs of 16.8% for opaque devices and 13.1% for semitransparent OSCs (AVT of 22.4% and infrared photon radiation rejection (IRR) of 77%). Further, multifunctional ST‐OSCs are realized via introducing simple, yet effective photonic reflectors, together with optical simulation, leading to not only perfect fitting of the visible transmittance peak (555 nm) to the photopic response of the human eye but also an excellent IRR of 90% (780–2500 nm), along with 23% AVT and over 12% PCE. This is thought to be the best‐performing multifunctional ST‐OSC with promising prospects as BIPVs in terms of power generation, heat dissipation, and being see‐through
Xie, Yuanpeng; Cai, Yunhao; Zhu, Lei; Xia, Ruoxi; Ye, Linglong; Feng, Xiang; Yip, Hin‐Lap; Liu, Feng; Lu, Guanghao; Tan, Songting; Sun, Yanming
Advanced Functional Materials, 2020, 30, 2002181
The development of semitransparent organic solar cells (ST‐OSCs) represents a significant step toward the commercialization of OSCs. However, the trade‐off between power conversion efficiency (PCE) and average visible transmittance (AVT) restricts further improvements of ST‐OSCs. Herein, it is demonstrated that a fibril network strategy can enable ST‐OSCs with a high PCE and AVT simultaneously. A wide‐bandgap polymer PBT1‐C‐2Cl that can self‐assemble into a fibril nanostructure is used as the donor and a near‐infrared small molecule Y6 is adopted as the acceptor. It is found that a tiny amount of PBT1‐C‐2Cl in the blend can form a high speed pathway for hole transport due to the well distributed fibril nanostructure, which increases the transmittance in the visible region. Meanwhile, the acceptor Y6 guarantees sufficient light absorption. Using this strategy, the optimized ST‐OSCs yield a high PCE of 9.1% with an AVT of over 40% and significant light utilization efficiency of 3.65% at donor/acceptor ratio of 0.25:1. This work demonstrates a simple and effective approach to realizing high PCE and AVT of ST‐OSCs simultaneously.
205. "Composition Engineering of All‐Inorganic Perovskite Film for Efficient and Operationally Stable Solar Cells"
Tian, Jingjing; Wang, Jing; Xue, Qifan; Niu, Tianqi; Yan, Lei; Zhu, Zonglong; Li, Ning; Brabec, Christoph J; Yip, Hin‐Lap; Cao, Yong
Advanced Functional Materials, 2020, 30, 2001764
Cesium‐based inorganic perovskites have recently attracted great research focus due to their excellent optoelectronic properties and thermal stability. However, the operational instability of all‐inorganic perovskites is still a main hindrance for the commercialization. Herein, a facile approach is reported to simultaneously enhance both the efficiency and long‐term stability for all‐inorganic CsPbI2.5Br0.5 perovskite solar cells via inducing excess lead iodide (PbI2) into the precursors. Comprehensive film and device characterizations are conducted to study the influences of excess PbI2 on the crystal quality, passivation effect, charge dynamics, and photovoltaic performance. It is found that excess PbI2 improves the crystallization process, producing high‐quality CsPbI2.5Br0.5 films with enlarged grain sizes, enhanced crystal orientation, and unchanged phase composition. The residual PbI2 at the grain boundaries also provides a passivation effect, which improves the optoelectronic properties and charge collection property in optimized devices, leading to a power conversion efficiency up to 17.1% with a high open‐circuit voltage of 1.25 V. More importantly, a remarkable long‐term operational stability is also achieved for the optimized CsPbI2.5Br0.5 solar cells, with less than 24% degradation drop at the maximum power point under continuous illumination for 420 h.
204. "Graded 2D/3D Perovskite Heterostructure for Efficient and Operationally Stable MA‐Free Perovskite Solar Cells"
Yao, Qin; Xue, Qifan; Li, Zhenchao; Zhang, Kaicheng; Zhang, Teng; Li, Ning; Yang, Shihe; Brabec, Christoph J; Yip, Hin‐Lap; Cao, Yong
Advanced Materials, 2020, 32, 2000571
Almost all highly efficient perovskite solar cells (PVSCs) with power conversion efficiencies (PCEs) of greater than 22% currently contain the thermally unstable methylammonium (MA) molecule. MA‐free perovskites are an intrinsically more stable optoelectronic material for use in solar cells but compromise the performance of PVSCs with relatively large energy loss. Here, the open‐circuit voltage (Voc) deficit is circumvented by the incorporation of β‐guanidinopropionic acid (β‐GUA) molecules into an MA‐free bulk perovskite, which facilitates the formation of quasi‐2D structure with face‐on orientation. The 2D/3D hybrid perovskites embed at the grain boundaries of the 3D bulk perovskites and are distributed through half the thickness of the film, which effectively passivates defects and minimizes energy loss of the PVSCs through reduced charge recombination rates and enhanced charge extraction efficiencies. A PCE of 22.2% (certified efficiency of 21.5%) is achieved and the operational stability of the MA‐free PVSCs is improved.
Li, Xue; Xia, Ruoxi; Yan, Kangrong; Yip, Hin-Lap; Chen, Hongzheng; Li, Chang-Zhi
Chinese Chemical Letters, 2020, 31, 1608-1611
Semitransparent organic solar cells (ST-OSCs) have the potentials to open promising applications that differ from those of conventional inorganic ones, such as see-through power windows with both energy generation and heat insulation functions. However, to achieve so, there remain significant challenges, especially for balancing critical parameters, such as power conversion efficiency (PCE), average visible transparency (AVT) and low energy infrared photon radiation rejection (IRR) to realize the full potentials of ST-OSCs. Herein, we demonstrate the new design of ST-OSCs through the rational integration of organic materials, transparent electrode and infrared photon reflector in one device. With the assistance of optical simulation, new ST-OSCs with precise layout exhibit state-of-art performance, with near 30% AVT and PCE of 7.3%, as well as an excellent IRR of over 93% (780–2500 nm), representing one of best multifunctional ST-OSCs with promising perspective for window application.
Shen, Liang; Yip, Hin-Lap; Gao, Feng; Ding, Liming
Sci. Bull., 2020, 65, 980-982
Two states for perovskite smart windows (strong light absorption vs. high transmission) can be switched back and forth in response to external environment to meet different needs.
201. "Toward Efficient Triple-Junction Polymer Solar Cells through Rational Selection of Middle Cells"
Chen, Fang-Xiao; Qin, Ran; Xia, Ruoxi; Zhang, Yingzhu; Zuo, Lijian; Yip, Hin-Lap; Chen, Hongzheng; Li, Chang-Zhi
ACS Energy Letter, 2020, 5, 1771–1779
Li, Danyang; Wang, Junjie; Li, Miaozi; Xie, Gancheng; Guo, Biao; Mu, Lan; Li, Haiyang; Wang, Jian; Yip, Hin‐Lap; Peng, Junbiao
Adv. Mater. Technol., 2020, 5, 2000099
The photon energy losses of polymer solar cells (PSCs) routinely drag their experimental power conversion efficiencies (PCEs) far below the theoretical limits. We report herein efficient triple-junction PSCs (TJ-PSCs) with mitigated energy losses through rational selection of subcells. We reveal that avoiding strong photon competition between the front and middle cells is critical in balancing the absorption rate among subcells with realistic layer thicknesses. Efficient TJ-PSCs are achieved by stacking a front cell of PBDB-T-2F:PC71BM, a middle cell of PBDB-T:HF-TCIC, and a rear cell of PTB7-Th: IEICO-4F in series and connecting them with two functional interconnection layers. A PCE of 13.09% is obtained from champion devices, representing one of the best TJ-PSCs among the reported studies. It accounts for a 35% improvement in efficiency over those of single-junction PSCs with the same absorption range, which is mainly attributed to the reduced nonabsorbing and thermalization losses of TJ-PSCs.