2018 | yipgroup

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

All‐polymer solar cells (all‐PSCs) that contain both p‐type and n‐type polymeric materials blended together as light‐absorption layers have attracted much attention, since the blend of a polymeric donor and acceptor should present superior photochemical, thermal, and mechanical stability to those of small molecular‐based organic solar cells. In this work, the interfacial stability is studied by using highly stable all‐polymer solar cell as a platform. It is found that the thermally deposited metal electrode atoms can diffuse into the active layer during device storage, which consequently greatly decreases the power conversion efficiency. Fortunately, the diffusion of metal atoms can be slowed down and even blocked by using thicker interlayer materials, high‐glass‐transition‐temperature interlayer materials, or a tandem device structure. Learning from this, homojunction tandem all‐PSCs are successfully developed that simultaneously exhibit a record power conversion efficiency over 11% and remarkable stability with efficiency retaining 93% of the initial value after thermally aging at 80 °C for 1000 h.

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

In this work, a SnO2/ZnO bilayered electron transporting layer (ETL) aimed to achieve low energy loss and large open‐circuit voltage (V oc) for high‐efficiency all‐inorganic CsPbI2Br perovskite solar cells (PVSCs) is introduced. The high‐quality CsPbI2Br film with regular crystal grains and full coverage can be realized on the SnO2/ZnO surface. The higher‐lying conduction band minimum of ZnO facilitates desirable cascade energy level alignment between the perovskite and SnO2/ZnO bilayered ETL with superior electron extraction capability, resulting in a suppressed interfacial trap‐assisted recombination with lower charge recombination rate and greater charge extraction efficiency. The as‐optimized all‐inorganic PVSC delivers a high V oc of 1.23 V and power conversion efficiency (PCE) of 14.6%, which is one of the best efficiencies reported for the Cs‐based all‐inorganic PVSCs to date. More importantly, decent thermal stability with only 20% PCE loss is demonstrated for the SnO2/ZnO‐based CsPbI2Br PVSCs after being heated at 85 °C for 300 h. These findings provide important interface design insights that will be crucial to further improve the efficiency of all‐inorganic PVSCs in the future.

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

Tandem perovskite solar cells are an effective concept to overcome the Shockley–Queisser limit of a single-junction perovskite solar cell. For a high-performance tandem cell, besides a wide-bandgap perovskite top cell, a high-quality low-bandgap perovskite bottom cell with an optimum bandgap of ∼1.2 eV is urgently needed. Moreover, a simple process technique needs to be developed for a high-quality perovskite film with good reproducibility, in order to further simplify the whole tandem-cell fabrication. Accordingly, we develop a simple one-step process (vacuum-assisted thermal annealing) for a high-quality low-bandgap CH3NH3Sn0.5Pb0.5IxCl3−x film, where the absorption edge can exceed 1000 nm. After comparing CH3NH3Sn0.5Pb0.5IxCl3−x films annealed in a vacuum and in a nitrogen environment, we find that vacuum-assisted thermal annealing can result in CH3NH3Sn0.5Pb0.5IxCl3−x films with better film coverage and crystallinity. This process can also accelerate the sublimation of methylammonium chloride and reduce the trap density in the CH3NH3Sn0.5Pb0.5IxCl3−x film. With this process, we successfully fabricated an efficient low-bandgap perovskite solar cell with a power conversion efficiency of more than 12% and good device reproducibility as well as long-term stability.

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

Solution-processed electroluminescent tandem white quantum-dot light-emitting diodes (TWQLEDs) have the advantages of being low-cost and high-efficiency and having a wide color gamut combined with color filters, making this a promising backlight technology for high-resolution displays. However, TWQLEDs are rarely reported due to the challenge of designing device structures and the deterioration of film morphology with component layers that can be deposited from solutions. Here, we report an interconnecting layer with the optical, electrical, and mechanical properties required for fully solution-processed TWQLED. The optimized TWQLEDs exhibit a state-of-the-art current efficiency as high as 60.4 cd/A and an extremely high external quantum efficiency of 27.3% at a luminance of 100 000 cd/m2. A high color gamut of 124% NTSC 1931 standard can be achieved when combined with commercial color filters. These results represent the highest performance for solution-processed WQLEDs, unlocking the great application potential of TWQLEDs as backlights for new-generation displays.

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

Lead (Pb)-based halide perovskites with enhanced solar cell performance and a larger open-circuit voltage were experimentally observed after the treatment of crystal surfaces with pyridine and amine-functionalized molecules. We model the Pb–I2 terminated perovskite surfaces using density-functional theory and find that two small organic molecules, pyridine and ethylamine, interact with the surfaces and tune their electronic band gaps. When dopants on surfaces have parallel or antiparallel polarities with the orientation of methylammonium (MA = CH3NH3) molecules in bulk, the electronic properties of the perovskite surfaces will be remarkably different. We demonstrate that ethylamine and pyridine with antiparallel polarities can enlarge the band gaps of perovskite surfaces. The change of electronic properties is ascribed to the cancellation of the dipole moments caused by the pyridine/ethylamine and methylammonium molecules on surfaces. We further vary the polarities of MA molecules by interchanging the C and N atoms in a symmetric fashion for showing the influence of polarization on total energies, electronic properties and charge distributions.

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

In the field of organic solar cells (OSCs), tandem structure devices exhibit very attractive advantages for improving power conversion efficiency (PCE). In addition to the well researched novel pair of active layers in different subcells, the construction of interconnecting layer (ICL) also plays a critical role in achieving high performance tandem devices. In this work, a new way of achieving environmentally friendly solvent processed polymeric ICL by adopting poly[(9,9‐bis(3′‐(N,N ‐dimethylamino)propyl)‐2,7‐fluorene)‐alt‐5,5′‐bis(2,2′‐thiophene)‐2,6‐naphthalene‐1,4,5,8‐tetracaboxylic‐N,N ′‐di(2‐ethylhexyl)imide] (PNDIT‐F3N) blended with poly(ethyleneimine) (PEI) as the electron transport layer (ETL) and PEDOT:PSS as the hole transport layer is reported. It is found that the modification ability of PNDIT‐F3N on PEDOT can be linearly tuned by the incorporation of PEI, which offers the opportunity to study the charge recombination behavior in ICL. At last, tandem OSC with highest PCE of 12.6% is achieved, which is one of the best tandem OSCs reported till now. These results offer a new selection for constructing efficient ICL in high performance tandem OSCs and guide the way of design new ETL materials for ICL construction, and may even be integrated in future printed flexible large area module device fabrication with the advantages of environmentally friendly solvent processing and thickness insensitivity.

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

Low‐cost wide‐bandgap solar cells are attractive candidates for potential applications including tandem photovoltaics, solar‐driven electrochemical energetic devices, and photovoltaic solar panels for spacecraft due to their relatively high output voltage and sustainability in critical environment. Recently, solar cells based on the organic–inorganic lead halide perovskites have emerged as a promising avenue toward high power conversion efficiency (PCE). However, the investigations on achieving high operating voltage with sufficient output power remains a missing part for the halide perovskite solar cells. Here the effectiveness of employing both anode and cathode interfacial modification layers to reach high open‐circuit voltage (V OC) for the methylammonium lead tribromide (MAPbBr3) perovskite solar cells is demonstrated. Specifically, high work function e‐beam processed MoOx layer with vacuum annealing treatment is used to reengineer the anode interface and an atomic layer deposited ZrO2 layer is used to modify the cathode interface, respectively. The minimized energy barrier height by MoOx modification and hole‐blocking effect by ZrO2 synergistically restrain the charge carrier recombination loss and render a consequent larger quasi‐Fermi level separation that endows a higher V OC. The MAPbBr3 perovskite solar cell with a highest PCE of 10.08% and a new record V OC of 1653 mV under one sun‐illumination are demonstrated.

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

Fabricating solar cells with tandem structure is an efficient way to broaden the photon response range without further increasing the thermalization loss in the system. In this work, a tandem organic solar cell (TOSC) based on highly efficient nonfullerene acceptors (NFAs) with series connection type is demonstrated. To meet the different demands of front and rear sub‐cells, two NFAs named F‐M and NOBDT with a whole absorption range from 300 to 900 nm are designed, when blended with wide bandgap polymer poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithiophene))‐alt ‐(5,5‐(1′,3′‐di‐2‐thienyl‐5′,7′‐bis(2‐ethylhexyl)benzo[1′,2′‐c:4′,5′‐c′]dithiophene‐4,8‐dione))] (PBDB‐T) and narrow bandgap polymer PTB7‐Th, respectively, the PBDB‐T: F‐M system exhibits a high V oc of 0.98 V and the PTB7‐Th: NOBDT system shows a remarkable J sc of 19.16 mA cm−2, which demonstrate their potential in the TOSCs. With the guidance of optical simulation, by systematically optimizing the thickness of each layer in the TOSC, an outstanding power conversion efficiency of 14.11%, with a V oc of 1.71 V, a J sc of 11.72 mA cm−2, and a satisfactory fill factor of 0.70 is achieved; this result is one of the top efficiencies reported to date in the field of organic solar cells.

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

Semi-transparent photovoltaic (ST-PV) technologies can be applied to replace facades and roofs in conventional buildings and coatings on vehicles to produce energy from sunlight. Current ST-PV technology is Si-based, but although Si achieves adequate efficiencies, it compromises on aesthetic appeal; its color is intrinsically difficult to tune. However, this presents an opportunity for semi-transparent polymer and perovskite-based PVs, the optical properties of which can be modulated easily by tuning their material compositions. In this review article, we summarize recent progress made in the material selection, optical engineering and device architecture design for high-performance, semi-transparent polymer and perovskite solar cells and discuss challenges for the commercialization of these semi-transparent solar cells for power-generating applications in windows.

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, 6, 4457-4463

In recent years, the use of non-fullerene acceptors in organic solar cells has rapidly advanced with new acceptor materials, which have enabled devices to achieve a power conversion efficiency greater than 13%. In addition to new acceptor materials’ design, device engineering plays an important role in improving the device performance. In this study, we develop effective device engineering strategies, including thermal annealing and interlayer modification, to improve the device performance from 7.39% to 9.39%. With the use of PTB7-Th as the donor and IDT-BT-R as the non-fullerene acceptor, we achieved an efficient non-fullerene organic solar cell based on an inverted device architecture with a power conversion efficiency as high as 9.39%. It is worthy of note that the energy loss of the optimized device is only around 0.5 eV, which can be attributed to weak recombination and the appropriate high energy level of the charge transfer states within the optimized device.

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, 9, 2698-2704

Significant efforts have been devoted to developing new dopant-free hole transporting materials (HTMs) for perovskite solar cells (PVSCs). Fluoranthene is one typical cyclopentene-fused polycyclic aromatic hydrocarbon with a rigid planarized structure, and thus could be an ideal building block to construct dopant-free HTMs, which have not been reported yet. Here, we report a new and simple synthetic method to prepare unreported 2,3-dicyano-fluoranthene through a Diels–Alder reaction between dibenzofulvene and tetracyanoethylene, and demonstrate that it can serve as an efficient electron-withdrawing unit for constructing donor–acceptor (D–A) type HTMs. This novel building block not only endows the resulting molecules with suitable energy levels, but also enables highly ordered and strong molecular packing in solid states, both of which could facilitate hole extraction and transport. Thus with dopant-free HTMs, impressive efficiencies of 18.03% and 17.01% which are associated with enhanced stability can be achieved based on conventional n–i–p and inverted p–i–n PVSCs respectively, outperforming most organic dopant-free HTMs reported so far.

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, 2, 1700169

While the performance of laboratory‐scale organic solar cells (OSCs) continues to grow, development of high efficiency large area OSCs remains a big challenge. Although a few attempts to produce large area organic solar cells (OSCs) have been reported, there are still challenges on the way to realizing efficient module devices, such as the low compatibility of the thickness‐sensitive active layer with large area coating techniques, the frequent need for toxic solvents and tedious optimization processes used during device fabrication. In this work, highly efficient thickness‐insensitive OSCs based on PTB7‐Th:PC71BM that processed with single‐component green solvent 2‐methylanisole are presented, in which both junction thickness limitation and solvent toxicity issues are simultaneously addressed. Careful investigation reveals that this green solvent prevents the evolution of PC71BM into large area clusters resulting in reduced charge carrier recombination, and largely eliminates trapping centers, and thus improves the thickness tolerance of the films. These findings enable us to address the scalability and solvent toxicity issues and to fabricate a 16 cm2 OSC with doctor‐blade coating with a state‐of‐the‐art power conversion efficiency of 7.5% using green solvent.

~ 2018 ~

Google Scholar: https://scholar.google.com/citations?hl=en&user=FJ51C38AAAAJ

Publons: https://publons.com/researcher/2761941/hin-lap-yip/

Researchgate: https://www.researchgate.net/profile/Hin-Lap_Yip

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