Low-band-gap metal halide perovskite semiconductor based on mixed Sn/Pb is a key component to realize high-efficiency tandem perovskite solar cells. However, the mixed perovskites are unstable in air due to the oxidation of Sn2+. To overcome the stability problem, we introduced N-(3-aminopropyl)-2-pyrrolidinone into the CH3NH3Sn0.5Pb0.5IxCl3-x thin film. The carbonyl group on the molecule interacts with Sn2+/Pb2+ by Lewis acid coordination, forming vertically oriented 2D layered perovskite. The 2D phase is seamlessly connected to the bulk perovskite crystal, with a lattice coherently extending across the two phases. Based on this 2D/3D hybrid structure, we assembled low-band-gap Sn-based perovskite solar cells with power conversion efficiency greater than 12%. The best device was among the most stable Sn-based organic-inorganic hybrid perovskite solar cells to date, keeping 90% of its initial performance at ambient condition without encapsulation, and more than 70% under continuous illumination in an N2-filled glovebox for over 1 month.

153. "Stable Sn/Pb-based perovskite solar cells with a coherent 2D/3D interface"

Chen, Ziming; Liu, Meiyue; Li, Zhenchao; Shi, Tingting; Yang, Yongchao; Yip, Hin-Lap; Cao, Yong

iScience, 2018,9, 337-346

Solar photon‐to‐electron conversion with polymer solar cells (PSCs) has experienced rapid development in the recent few years. Even so, the exploration of molecules and devices in efficiently converting near‐infrared (NIR) photons into electrons remains critical, yet challenging. Herein presented is a family of near‐infrared nonfullerene acceptors (NIR NFAs, T1–T4) with fluorinated regioisomeric A–Aπ–D–Aπ–A backbones for constructing efficient single‐junction and tandem PSCs with photon response up to 1000 nm. It is found that the tuning of the regioisomeric bridge (Aπ) and fluoro (F)‐substituents on a molecular skeleton strongly influences the backbone conformation and conjugation, leading to the optimized optoelectronic and stable stacking of resultant NFAs, which eventually impacts the performance of derived PSCs. In PSCs, the proximal NFAs with varied F‐atoms (T1–T3) mostly outperform than that of distal NFA (T4). Notably, single‐junction PSC with PTB7‐Th:T2 blend can reach 10.87% power conversion efficiency (PCE), after implementing a solvent additive to improve blend morphology. Moreover, efficient tandem PSCs are fabricated through integrating such NIR cells with mediate bandgap nonfullerene‐based subcells, to achieve a PCE of 14.64%. The results reveal the structural design of organic semiconductor and device with improved photovoltaic performance.

152. "Near‐Infrared Electron Acceptors with Fluorinated Regioisomeric Backbone for Highly Efficient Polymer Solar Cells"

Chen, Fang‐Xiao; Xu, Jing‐Qi; Liu, Zhi‐Xi; Chen, Ming; Xia, Ruoxi; Yang, Yongchao; Lau, Tsz‐Ki; Zhang, Yingzhu; Lu, Xinhui; Yip, Hin‐Lap; Alex K‐Y; Chen, Hongzhen; Li, Changzhi

Advanced Materials, 2018,30, 1803769

In the past few years, substantial progress has been made in perovskite light-emitting devices. Both pure green and infrared thin-film perovskite light-emitting devices with external quantum efficiencyover 20% have been successfully achieved. However, pure-red and blue thin-film perovskite light-emitting diodes still suffer from inferior efficiency. Therefore, the development of efficient and stable thin-film perovskite light-emitting diodes with pure-red and blue emissions is urgently needed for possible applications as a new display technology and solid-state lighting. Here, we demonstrate an efficient light-emitting diode with pure-red emission based on polymer-assisted in situ growth of high-quality all-inorganic CsPbBr0.6I2.4 perovskite nanocrystal films with homogenous distribution of nanocrystals with size 20–30 nm. With this method, we can dramatically reduce the formation temperature of CsPbBr0.6I2.4 and stabilize its perovskite phase. Eventually, we successfully demonstrate a pure-red-emission perovskite light-emitting diode with a high external quantum efficiency of 6.55% and luminance of 338 cd/m2. Furthermore, the device obtains an ultralow turn-on voltage of 1.5 V and a half-lifetime of over 0.5 h at a high initial luminance of 300 cd/m2.

151. "Polymer-assisted in situ growth of all-inorganic perovskite nanocrystal film for efficient and stable pure-red light-emitting devices"

Cai, Wanqing; Chen, Ziming; Li, Zhenchao; Yan, Lei; Zhang, Donglian; Liu, Linlin; Xu, Qing-hua; Ma, Yuguang; Huang, Fei; Yip, Hin-Lap; Cao, Yong

ACS Applied Materials & Interfaces, 2018,10, 42564-42572

The field of organic–inorganic hybrid perovskite light‐emitting diodes (PeLEDs) has developed rapidly in recent years. Although the performance of PeLEDs continues to improve through film quality control and device optimization, little research has been dedicated to understanding the recombination dynamics in perovskite thin films. Likewise, little has been done to investigate the effects of recombination dynamics on the overall light‐emitting behavior of PeLEDs. Therefore, this study investigates the recombination dynamics of CH3NH3PbI3 thin films with differing crystal sizes by measurement of fluence‐dependent transient absorption dynamics and time‐resolved photoluminescence. The aim is to find out the link between recombination dynamics and device behavior in PeLEDs. It is found that bimolecular and Auger recombination become more efficient as the crystal size decreases and monomolecular recombination rate is affected by the trap density of perovskite. By defining the radiative efficiency Φ(n ), which relates to the monomolecular, bimolecular, and Auger recombination, the fundamental recombination properties of CH3NH3PbI3 films are discerned in quantitative terms. These findings help us to understand the light emission behavior of PeLEDs. This study takes an important step toward establishing the relationship between film structure, recombination dynamics, and device behavior for PeLEDs, thereby providing useful insights toward the design of better perovskite devices.

150. "Recombination Dynamics Study on Nanostructured Perovskite Light‐Emitting Devices"

Chen, Ziming; Li, Zhenchao; Zhang, Chongyang; Jiang, Xiao‐Fang; Chen, Dongcheng; Xue, Qifan; Liu, Meiyue; Su, Shijian; Yip, Hin‐Lap; Cao, Yong

Advanced Materials, 2018,30, 1801370

Commercial heat-control window films applied to the interior or exterior of glass windows to reduce the amount of UV, visible, and infrared light from sunlight are already widely used to improve energy efficiency of buildings, while semitransparent organic photovoltaics (ST-OPVs) have not yet been commercialized for power-generating window applications.

Here we have demonstrated for the first time that power-generation and heat-insulation functions can indeed be integrated together in specially designed ST-OPVs, which not only provide good power-generation properties but also show heat rejection comparable with that of commercial window films. A value-added ST-OPV with high PCE and AVT in addition to an excellent infrared radiation rejection rate have been demonstrated, which paves the way for the new application of OPV technology for both power generation and power saving.

149. "Heat-insulating multifunctional semitransparent polymer solar cells"

Sun, Chen; Xia, Ruoxi; Shi, Hui; Yao, Huifeng; Liu, Xiang; Hou, Jianhui; Huang, Fei; Yip, Hin-Lap; Cao, Yong

Joule, 2018, 2, 1816-1826

Tandem solar cells can boost efficiency by using a wider range of the solar spectrum. The bandgap of organic semiconductors can be tuned over a wide range, but, for a two-terminal device that directly connects the cells, the currents produced must be nearly equal. Meng et al. used a semiempirical analysis to choose well-matched top- and bottom-cell active layers. They used solution processing to fabricate an inverted tandem device that has a power conversion efficiency as high as 17.4%.

148. "Organic and solution-processed tandem solar cells with 17.3% efficiency"

Meng, Lingxian; Zhang, Yamin; Wan, Xiangjian; Li, Chenxi; Zhang, Xin; Wang, Yanbo; Ke, Xin; Xiao, Zuo; Ding, Liming; Xia, Ruoxi

Science, 2018, 361, 1094-1098

147. "11.2% All‐polymer tandem solar cells with simultaneously improved efficiency and stability"

Zhang, Kai; Xia, Ruoxi; Fan, Baobing; Liu, Xiang; Wang, Zhenfeng; Dong, Sheng; Yip, Hin‐Lap; Ying, Lei; Huang, Fei; Cao, Yong

Advanced Materials, 2018,30, 1803166

146. "Overcoming Space‐Charge Effect for Efficient Thick‐Film Non‐Fullerene Organic Solar Cells"

Zhang, Guichuan; Xia, Ruoxi; Chen, Zhen; Xiao, Jingyang; Zhao, Xuenan; Liu, Shiyuan; Yip, Hin‐Lap; Cao, Yong

Advanced Energy Materials, 2018, 8, 1801609

Organic solar cells (OSCs) containing non‐fullerene acceptors have realized high power conversion efficiency (PCE) up to 14%. However, most of these high‐performance non‐fullerene OSCs have been reported with optimal active layer thickness of about 100 nm, mainly due to the low electron mobility (≈10−4–10−5 cm2 V−1 s−1) of non‐fullerene acceptors, which are not suitable for roll‐to‐roll large‐scale processing. In this work, an efficient non‐fullerene OSC based on poly[(5,6‐difluoro‐2,1,3‐benzothiadiazol‐4,7‐diyl)‐alt‐(3,3′″‐di(2‐octyldodecyl)‐2,2′;5′,2″;5″,2′″‐quaterthiophen‐5,5′′′‐diyl)] (PffBT4T‐2OD):EH‐IDTBR (consists of electron‐rich indaceno[1,2‐b:5,6‐b′]dithiophene as the central unit and an electron‐deficient 5,6‐benzo[c][1,2,5]thiadiazole unit flanked with rhodanine as the peripheral group) with thickness‐independent PCE (maintaining a PCE of 9.1% with an active layer thickness of 300 nm) is presented by optimizing device architectures to overcome the space‐charge effects. Optical modeling reveals that most of the incident light is absorbed near the transparent electrode side in thick‐film devices. The transport distance of electrons with lower mobility will therefore be shortened when using inverted device architecture, in which most of the excitons are generated close to the cathode side and therefore substantially reduces the accumulation of electrons in the device. As a result, an efficient thick‐film non‐fullerene OSC is realized. These results provide important guidelines for the development of more efficient thick‐film non‐fullerene OSCs.

145. "Interface Engineering for All‐Inorganic CsPbI2Br Perovskite Solar Cells with Efficiency over 14%"

Yan, Lei; Xue, Qifan; Liu, Meiyue; Zhu, Zonglong; Tian, Jingjing; Li, Zhenchao; Chen, Zhen; Chen, Ziming; Yan, He; Yip, Hin‐Lap; Cao, Yong

Advanced Materials, 2018, 30, 1802509

144. "High performance low-bandgap perovskite solar cells based on a high-quality mixed Sn–Pb perovskite film prepared by vacuum-assisted thermal annealing"

Liu, Meiyue; Chen, Ziming; Xue, Qifan; Cheung, Sin Hang; So, Shu Kong; Yip, Hin-Lap; Cao, Yong

Journal of Materials Chemistry A, 2018, 6, 16347-16354

143. " "Fully solution-processed tandem white quantum-dot light-emitting diode with an external quantum efficiency exceeding 25%

Jiang, Congbiao; Zou, Jianhua; Liu, Yu; Song, Chen; He, Zhiwei; Zhong, Zhenji; Wang, Jian; Yip, Hin-Lap; Peng, Junbiao; Cao, Yong

ACS Nano, 2018, 12, 6040-6049

142. "The electronic properties of CH 3 NH 3 PbI 3 perovskite surfaces tuned by inverted polarities of pyridine and ethylamine"

Shi, Tingting; Teng, Qiang; Yang, Xiao-Bao; Yip, Hin-Lap; Zhao, Yu-Jun

Journal of Materials Chemistry C, 2018, 6, 6733-6738

141. "Highly efficient tandem organic solar cell enabled by environmentally friendly solvent processed polymeric interconnecting layer"

Zhang, Kai; Fan, Baobing; Xia, Ruoxi; Liu, Xiang; Hu, Zhicheng; Gu, Honggang; Liu, Shiyuan; Yip, Hin‐Lap; Ying, Lei; Huang, Fei; Cao, Yong

Advanced Energy Materials, 2018, 8, 1703180

140. "Wide‐Bandgap Perovskite Solar Cells With Large Open‐Circuit Voltage of 1653 mV Through Interfacial Engineering"

Hu, Xiaowen; Jiang, Xiao‐Fang; Xing, Xiaobo; Nian, Li; Liu, Xiaoyang; Huang, Rong; Wang, Kai; Yip, Hin‐Lap; Zhou, Guofu 

Solar RRL, 2018, 2, 1800083

139. "Efficient and stable perovskite solar cells via dual functionalization of dopamine semiquinone radical with improved trap passivation capabilities"

Xue, Qifan; Liu, Meiyue; Li, Zhenchao; Yan, Lei; Hu, Zhicheng; Zhou, Jiawen; Li, Wenqiang; Jiang, Xiao‐Fang; Xu, Baomin; Huang, Fei; Li, Yuan; Yip, Hin‐Lap; Cao, Yong

Advanced Functional Materials, 2018, 28, 1707444

Highly efficient planar heterojunction perovskite solar cells (PVSCs) with dopamine (DA) semiquinone radical modified poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) (DA‐PEDOT:PSS) as a hole transporting layer (HTL) were fabricated. A combination of characterization techniques were employed to investigate the effects of DA doping on the electron donating capability of DA‐PEDOT:PSS, perovskite film quality and charge recombination kinetics in the solar cells. Our study shows that DA doping endows the DA‐PEDOT:PSS‐modified PVSCs with a higher radical content and greater perovskite to HTL charge extraction capability. In addition, the DA doping also improves work function of the HTL, increases perovskite film crystallinity, and the amino and hydroxyl groups in DA can interact with the undercoordinated Pb atoms on the perovskite crystal, reducing charge‐recombination rate and increasing charge‐extraction efficiency. Therefore, the DA‐PEDOT:PSS‐modified solar cells outperform those based on PEDOT:PSS, increasing open‐circuit voltage (V oc) and power conversion efficiency (PCE) to 1.08 V and 18.5%, respectively. Even more importantly, the efficiency of the unencapsulated DA‐PEDOT:PSS‐based PVSCs are well retained with only 20% PCE loss after exposure to air for 250 hours. These in‐depth insights into structure and performance provide clear and novel guidelines for the design of effective HTLs to facilitate the practical application of inverted planar heterojunction PVSCs.

138. "Nonfullerene tandem organic solar cells with high performance of 14.11%"

Zhang, Yamin; Kan, Bin; Sun, Yanna; Wang, Yanbo; Xia, Ruoxi; Ke, Xin; Yi, Yuan‐Qiu‐Qiang; Li, Chenxi; Yip, Hin‐Lap; Wan, Xiangjian; Cao, Yong; Chen, Yongshen

Advanced Materials, 2018, 30, 1707508

137. "Recent advances in semi-transparent polymer and perovskite solar cells for power generating window applications"

Xue, Qifan; Xia, Ruoxi; Brabec, Christoph J; Yip, Hin-Lap

Energy & Environmental Science, 2018, 11, 1688-1709

136. "Efficient device engineering for inverted non-fullerene organic solar cells with low energy loss"

Xiao, Jingyang; Chen, Ziming; Zhang, Guichuan; Li, Qing-Ya; Yin, Qingwu; Jiang, Xiao-Fang; Huang, Fei; Xu, Yun-Xiang; Yip, Hin-Lap; Cao, Yong

Journal of Materials Chemistry C, 2018, 64457-4463

135. "Fluoranthene-based dopant-free hole transporting materials for efficient perovskite solar cells"

Sun, Xianglang; Xue, Qifan; Zhu, Zonglong; Xiao, Qi; Jiang, Kui; Yip, Hin-Lap; Yan, He

Chemical science, 2018, 92698-2704

134. "Efficient large area organic solar cells processed by blade‐coating with single‐component green solvent"

Zhang, Kai; Chen, Zhiming; Armin, Ardalan; Dong, Sheng; Xia, Ruoxi; Yip, Hin‐Lap; Shoaee, Safa; Huang, Fei; Cao, Yong 

Solar RRL, 2018, 21700169

~ 2018 ~

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