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Yip Group @ CityU HK

Hybrid and Organic Materials for Energy Applications

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

133. "Synergic Interface and Optical Engineering for High‐Performance Semitransparent Polymer Solar Cells"

Shi, Hui; Xia, Ruoxi; Sun, Chen; Xiao, Jingyang; Wu, Zhihong; Huang, Fei; Yip, Hin‐Lap; Cao, Yong

Advanced Energy Materials, 2017, 7, 1701121

In this study the thickness of the PTB7‐Th:PC71BM bulk heterojunction (BHJ) film and the PF3N‐2TNDI electron transport layer (ETL) is systematically tuned to achieve polymer solar cells (PSCs) with optimized power conversion efficiency (PCE) of over 9% when an ultrathin BHJ of 50 nm is used. Optical modeling suggests that the high PCE is attributed to the optical spacer effect from the ETL, which not only maximizes the optical field within the BHJ film but also facilitates the formation of a more homogeneously distributed charge generation profile across the BHJ film. Experimentally it is further proved that the extra photocurrent produced at the PTB7‐Th/PF3N‐2TNDI interface also contributes to the improved performance. Taking advantage of this high performance thin film device structure, one step further is taken to fabricate semitransparent PSCs (ST‐PSCs) by using an ultrathin transparent Ag cathode to replace the thick Ag mirror cathode, yielding a series of high performance ST‐PSCs with PCEs over 6% and average visible transmittance between 20% and 30%. These ST‐PSCs also possess remarkable transparency color perception and rendering properties, which are state‐of‐the‐art and fulfill the performance criteria for potential use as power‐generating windows in near future.

~ 2017 ~

132. "Naphthalene diimide based n-type conjugated polymers as efficient cathode interfacial materials for polymer and perovskite solar cells"

Jia, Tao; Sun, Chen; Xu, Rongguo; Chen, Zhiming; Yin, Qingwu; Jin, Yaocheng; Yip, Hin-Lap; Huang, Fei; Cao, Yong

ACS Applied Materials & Interfaces, 2017, 9, 36070-36081

A series of naphthalene diimide (NDI) based n-type conjugated polymers with amino-functionalized side groups and backbones were synthesized and used as cathode interlayers (CILs) in polymer and perovskite solar cells. Because of controllable amine side groups, all the resulting polymers exhibited distinct electronic properties such as oxidation potential of side chains, charge carrier mobilities, self-doping behaviors, and interfacial dipoles. The influences of the chemical variation of amine groups on the cathode interfacial effects were further investigated in both polymer and perovskite solar cells. We found that the decreased electron-donating property and enhanced steric hindrance of amine side groups substantially weaken the capacities of altering the work function of the cathode and trap passivation of the perovskite film, which induced ineffective interfacial modifications and declining device performance. Moreover, with further improvement of the backbone design through the incorporation of a rigid acetylene spacer, the resulting polymers substantially exhibited an enhanced electron-transporting property. Upon use as CILs, high power conversion efficiencies (PCEs) of 10.1% and 15.2% were, respectively, achieved in polymer and perovskite solar cells. Importantly, these newly developed n-type polymers were allowed to be processed over a broad thickness range of CILs in photovoltaic devices, and a prominent PCE of over 8% for polymer solar cells and 13.5% for perovskite solar cells can be achieved with the thick interlayers over 100 nm, which is beneficial for roll-to-roll coating processes. Our findings contribute toward a better understanding of the structure–performance relationship between CIL material design and solar cell performance, and provide important insights and guidelines for the design of high-performance n-type CIL materials for organic and perovskite optoelectronic devices.

131. "Fabrication of high-performance and low-hysteresis lead halide perovskite solar cells by utilizing a versatile alcohol-soluble bispyridinium salt as an efficient cathode modifier"

Chen, Guiting; Zhang, Fan; Liu, Meiyue; Song, Jun; Lian, Jiarong; Zeng, Pengju; Yip, Hin-Lap; Yang, Wei; Zhang, Bin; Cao, Yong

Journal of Materials Chemistry A, 2017, 5, 17943-17953

A novel alcohol-soluble conjugated bispyridinium salt (FPyBr) is developed and used as a cathode modifier to improve the cathode interface of planar heterojunction perovskite solar cells (PHJ PVSCs). The excellent electron-withdrawing ability of bispyridinium rings endows FPyBr with a favorable energy level alignment with phenyl-C60-butyric acid methyl ester (PCBM) and the cathode (e.g., Al), which leads to an ideal ohmic contact and efficient electron transport and collection. The deep-lying highest occupied molecular orbital energy level of FPyBr can also effectively block hole carriers and thus decrease leakage current and hole–electron recombination at the cathode interface. In addition, FPyBr can n-dope PCBM through an anion-induced electron transfer process, which increases the electron mobility of PCBM drastically, thereby diminishing interfacial resistance and promoting electron transport. As a result, by incorporating an FPyBr cathode interlayer with ethanol solvent, high-performance and low-hysteresis PHJ PVSCs with a maximal power conversion efficiency (PCE) of 19.61% can be realized. In contrast, reference devices without any cathode interlayer display a distinctly worse performance, with a PCE of 16.97%. Therefore, this excellent cathode modifier provides a new opportunity to fabricate high performance multilayer PVSCs using low-temperature solution processing without interfacial erosion/mixing.

130. "Effects of organic cations on the defect physics of tin halide perovskites"

Shi, Tingting; Zhang, Hai-Shan; Meng, Weiwei; Teng, Qiang; Liu, Meiyue; Yang, Xiaobao; Yan, Yanfa; Yip, Hin-Lap; Zhao, Yu-Jun;

Journal of Materials Chemistry A, 2017, 5, 15124-15129

Tin (Sn) halide perovskite absorbers have attracted much interest because of their nontoxicity as compared to their lead (Pb) halide perovskite counterparts. Recent progress shows that the power conversion efficiency of FASnI3 (FA = HC(NH2)2) solar cells prevails over that of MASnI3 (MA = CH3NH3). In this paper, we show that the organic cations, i.e., FA and MA, play a vital role in the defect properties of Sn halide perovskites. The antibonding coupling between Sn-5s and I-5p is clearly weaker in FASnI3 than in MASnI3 due to the larger ionic size of FA, leading to higher formation energies of Sn vacancies in FASnI3. Subsequently, the conductivity of FASnI3 can be tuned from p-type to intrinsic by varying the growth conditions of the perovskite semiconductor; in contrast, MASnI3 shows unipolar high p-type conductivity independent of the growth conditions. This provides a reasonable explanation for the better performance of FASnI3-based solar cells in experiments with respect to the MASnI3-based solar cells.

129. "Combined optimization of emission layer morphology and hole-transport layer for enhanced performance of perovskite light-emitting diodes"

Meng, Fanyuan; Zhang, Chongyang; Chen, Dongcheng; Zhu, Weiguo; Yip, Hin-Lap; Su, Shi-Jian

Journal of Materials Chemistry C, 2017, 5, 6169-6175

Electroluminescence performance of perovskite light-emitting diodes (PeLEDs) is extremely dependent on the morphology of the perovskite films, which is influenced by the processing method. Herein, we report an effective approach for the preparation of a high-quality perovskite film with perfect performance for PeLEDs via a solution process at room temperature. On the one hand, CH3NH3PbBr3 (MAPbBr3) precursor solution was blended with a traditional polymeric host PVK [poly(vinylcarbazole)] to obtain smooth and uniform perovskite films. On the other hand, the perovskite films could be further improved through crystal modification to obtain a more uniform morphology and smaller grain sizes. Our research also demonstrated the feasibility of preparing high-performance solution-processed PeLEDs by blending small molecule hole-transport materials (HTMs) with polymer HTMs (widely used in OLEDs as hole-transport layers (HTLs)). Efficient green PeLEDs with a current efficiency (CE) of 6.7 cd A−1, external quantum efficiency (EQE) of 1.88%, and low turn-on voltage of 2.9 V were achieved; this indicates that the effective solution process used to improve the morphology of the perovskite films as well as carrier injection has great potential for the development of high-performance PeLEDs.

128. "Dual interfacial modifications enable high performance semitransparent perovskite solar cells with large open circuit voltage and fill factor"

Xue, Qifan; Bai, Yang; Liu, Meiyue; Xia, Ruoxi; Hu, Zhicheng; Chen, Ziming; Jiang, Xiao‐Fang; Huang, Fei; Yang, Shihe; Matsuo, Yutaka; Yip, Hin-Lap; Cao, Yong

Advanced Energy Materials, 2017, 7, 1602333

In this work, both anode and cathode interfaces of p‐i‐n CH3NH3PbI3 perovskite solar cells (PVSCs) are simultaneously modified to achieve large open‐circuit voltage (Voc) and fill factor (FF) for high performance semitransparent PVSCs (ST‐PVSCs). At the anode, modified NiO serves as an efficient hole transport layer with appropriate surface property to promote the formation of smooth perovskite film with high coverage. At the cathode, a fullerene bisadduct, C60(CH2)(Ind), with a shallow lowest unoccupied molecular orbital level, is introduced to replace the commonly used phenyl‐C61‐butyric acid methyl ester (PCBM) as an alternative electron transport layer in PVSCs for better energy level matching with the conduction band of the perovskite layer. Therefore, the Voc, FF and power conversion efficiency (PCE) of the PVSCs increase from 1.05 V, 0.74 and 16.2% to 1.13 V, 0.80 and 18.1% when the PCBM is replaced by C60(CH2)(Ind). With the advantages of high Voc and FF, ST‐PVSCs are also fabricated using an ultrathin transparent Ag as cathode, showing an encouraging PCEs of 12.6% with corresponding average visible transmittance (AVT) over 20%. These are the highest PCEs reported for ST‐PVSCs with similar AVTs paving the way for using ST‐PVSCs as power generating windows.

127. "Interface design for high-efficiency non-fullerene polymer solar cells"

Sun, Chen; Wu, Zhihong; Hu, Zhanhao; Xiao, Jingyang; Zhao, Wenchao; Li, Ho-Wa; Li, Qing-Ya; Tsang, Sai-Wing; Xu, Yun-Xiang; Zhang, Kai; Yip, Hin-Lap; Hou, Jianhui; Huang, Fei; Cao, Yong

Energy & Environmental Science, 2017, 10, 1784-1791

Non-fullerene polymer solar cells have attracted extensive attention due to their potential for overcoming the performance bottleneck currently encountered in fullerene-based photovoltaics. Herein, we report non-fullerene polymer solar cells with a maximal power conversion efficiency of over 11% by introducing an n-type water/alcohol soluble conjugated polymer as a cathode interlayer. We found that the contact between the n-type interlayer and the donor provides an extra interface for charge dissociation and the matching of energy levels between the n-type interlayer and the acceptor allows efficient electron extraction from the bulk heterojunction, which eventually leads to much improved performance. This study proposes a significant design rule for designing new interfaces for high performance non-fullerene photovoltaics.

126. "Interface Engineering of a Compatible PEDOT Derivative Bilayer for High‐Performance Inverted Perovskite Solar Cells"

Bao, Xichang; Wang, Junyi; Li, Yuan; Zhu, Dangqiang; Wu, Ying; Guo, Peipei; Wang, Xuefei; Zhang, Yongchao; Wang, Jiuxing; Yip, Hin‐Lap; Yang, Renqiang

Advanced Materials Interfaces, 2017, 4, 1600948

Interface engineering is an important aspect for the improvement of perovskite solar cells (PVSCs). The hole transport layer with good interface contact, transport capability, and matched energy level is indispensable and critical for high‐performance photovoltaic devices. Herein, anode interface engineering with an excellent compatible bilayer of poly(3,4‐ethylene dioxythiophene):poly(styrenesulfo‐nate)/poly(3,4‐ethylene dioxythiophene) (PEDOT:PSS/PEDOT) doped with grafted sulfonated‐acetone–formaldehyde lignin (PEDOT:GSL) via a low‐temperature and water‐soluble process is presented. As a water‐processable interface material, PEDOT:GSL exhibits higher conductivity, as well as better structural and electronic homogeneities compared with PEDTO:PSS. Consequently, the PEDOT:PSS/PEDOT:GSL bilayer with tuned energy level, optical properties, and the combination of the trap passivation of GSL at the anode/perovskite interface can greatly improve charge extraction ability and reduce the interface recombination. Simultaneously, the homogeneous perovskite film is fabricated through optimizing the annealing process. The device with the power conversion efficiency up to 17.80% is achieved, with 32.6% improvement compared to PEDOT:PSS‐only device (13.42%). Our success to achieve high‐performance inverted PVSCs provides new understanding of PEDOT:PSS, and also new guidelines for anode interface engineering to further advancement of PVSCs. This promising approach paves the way to realize solution processable highly efficient PVSCs for potential practical applications.

125. "Poly (3, 4‐Ethylenedioxythiophene): Methylnaphthalene Sulfonate Formaldehyde Condensate: The Effect of Work Function and Structural Homogeneity on Hole Injection/Extraction Properties"

Li, Yuda; Liu, Meiyue; Li, Yuan; Yuan, Kai; Xu, Lijia; Yu, Wei; Chen, Runfeng; Qiu, Xueqing; Yip, Hin‐Lap

Advanced Energy Materials, 2017, 7, 1601499

Poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is widely used as hole injection/extraction material in organic optoelectronics. However, there still exist drawbacks for PEDOT:PSS such as low work function (WF), poor structural and electrical homogeneity. To solve these problems, methylnaphthalene sulfonate formaldehyde condensate (MNSF) is applied, which has excellent dispersion property, branched chemical structure, and low cost, as dispersant and dopant instead of linear PSS to prepare PEDOT:MNSF. The hole injection/extraction capability of PEDOT:MNSF is systematically studied in organic optoelectronic devices. PEDOT:MNSF‐1:6 exhibits unexpected high device performance with a maxima current efficiency of 33.4 cd A−1 in blue phosphorescent organic light‐emitting diode and a power conversion efficiency of 13.1% in CH3NH3PbIxCl3−x‐based inverted perovskite solar cell, respectively. Compared with PEDOT:PSS, the relatively higher efficiency of PEDOT:MNSF‐1:6 is attributed mainly to its higher WF of 5.29 eV, structural and electrical homogeneity. Our research displays a promising future of MNSF as a cheap and widely available alternative of PSS. Moreover, a clear map is provided for the design of dopant for PEDOT considering the structure of dopant.

124. "High‐performance color‐tunable perovskite light emitting devices through structural modulation from bulk to layered film"

Chen, Ziming; Zhang, Chongyang; Jiang, Xiao‐Fang; Liu, Meiyue; Xia, Ruoxi; Shi, Tingting; Chen, Dongcheng; Xue, Qifan; Zhao, Yu‐Jun; Su, Shijian; Yip, Hin‐Lap; Cao, Yong

Advanced Materials, 2017, 29, 1603157

Adding 2‐phenoxyethylamine (POEA) into a CH3NH3PbBr3 precursor solution can modulate the organic–inorganic hybrid perovskite structure from bulk to layered, with a photoluminescence and electroluminescence shift from green to blue. Meanwhile, POEA can passivate the CH3NH3PbBr3 surface and help to obtain a pure CH3NH3PbBr3 phase, leading to an improvement of the external quantum efficiency to nearly 3% in CH3NH3PbBr3 LED.

123. "Thermally stable high performance non-fullerene polymer solar cells with low energy loss by using ladder-type small molecule acceptors"

Li, Qing-Ya; Xiao, Jingyang; Tang, Lu-Ming; Wang, Hua-Chun; Chen, Ziming; Yang, Zhiyong; Yip, Hin-Lap; Xu, Yun-Xiang

Organic Electronics, 2017, 44, 217-224

Two ladder-type small molecule acceptors IDT-BT-R and IDT-BT-R-CN are utilized in non-fullerene polymer solar cells by pairing with PTB7-Th as donor polymer, in which PTB7-Th:IDT-BT-R solar cells achieve high performance up to 8.3% with high voltage of 1.02 V and low energy loss of 0.59 eV. Thermal annealing triggered local rearrangement of ladder-type molecules in n-type phases of bulk heterojunction films, increased their absorption abilities and electron transport properties, therefore resulting in improved short-circuit current densities (Jscs) and fill factors (FFs), in contrast to fullerene-based solar cells which suffered from extensive aggregation of fullerenes upon annealing. The outstanding thermal stability, high performance and low energy loss demonstrated here show great potential of non-fullerene polymer solar cells.

122. "General design of self-doped small molecules as efficient hole extraction materials for polymer solar cells"

Xue, Yuyuan; Guo, Peipei; Yip, Hin-Lap; Li, Yuan; Cao, Yong

Journal of Materials Chemistry A, 2017, 5, 3780-3785

The development of high performance hole transport materials (HTMs) without a chemical dopant is critical to achieve long-term device durability. The general design of self-doping materials based on a phenolamine structure with strong electronic spin concentration is reported for the first time. A phenol-enhanced self-doped mechanism is also proposed. Compared to their precursors, dimethylphenolamine derivatives, TBP-OH4, TPD-OH4 and Spiro-OH8, displayed much higher spin concentration in their neutral states. Phenol acts as a hole trap in the traditional concept, however, the films of TBP-OH4, TPD-OH4 and Spiro-OH8 exhibited higher conductivities than those of methoxyl precursors. Meanwhile, phenolamine derivatives have good solublility in polar organic solvents and show good solvent resistance in chlorobenzene. Considering the relatively good band alignment, film-formation and solvent resistance against chlorobenzene, Spiro-OH8 and TPD-OH4 exhibited comparable performance with that of PEDOT:PSS-4083. Most importantly, a new generation of self-doped systems based on a phenolamine structure might provide new insight in developing efficient HTMs for organic electronics.

121. "Amino-functionalized conjugated polymer electron transport layers enhance the UV-photostability of planar heterojunction perovskite solar cells"

Li, Dan; Sun, Chen; Li, Hao; Shi, Hui; Shai, Xuxia; Sun, Qiang; Han, Junbo; Shen, Yan; Yip, Hin-Lap; Huang, Fei; Wang, Mingkui

Chemical Sciences, 2017, 8, 4587-4594

In this study, for the first time, we report a solution-processed amino-functionalized copolymer semiconductor (PFN-2TNDI) with a conjugated backbone composed of fluorine, naphthalene diimide, and thiophene spacers as the electron transporting layer (ETL) in n–i–p planar structured perovskite solar cells. Using this copolymer semiconductor in conjunction with a planar n–i–p heterojunction, we achieved an unprecedented efficiency of ∼16% under standard illumination test conditions. More importantly, the perovskite devices using this polymer ETL have shown good stability under constant ultra violet (UV) light soaking during 3000 h of accelerated tests. Various advanced spectroscopic characterizations, including ultra-fast spectroscopy, ultra-violet photoelectron spectroscopy and electronic impedance spectroscopy, elucidate that the interaction between the functional polymer ETL and the perovskite layer plays a critical role in trap passivation and thus, the device UV-photostability. We expect that these results will boost the development of low temperature solution-processed organic ETL materials, which is essential for the commercialization of high-performance and stable, flexible perovskite solar cells.

120. "Solution-processed organic tandem solar cells with power conversion efficiencies> 12%"

Li, Miaomiao; Gao, Ke; Wan, Xiangjian; Zhang, Qian; Kan, Bin; Xia, Ruoxi; Liu, Feng; Yang, Xuan; Feng, Huanran; Ni, Wang; Wang, Yunchuang; Peng, Jiajun; Zhang, Hongtao; Liang Ziqi; Yip, Hin-Lap; Peng, Xiaobin; Cao, Yong; Chen, Yongshen

Nature Photonics, 2017, 11, 85-90

An effective way to improve the power conversion efficiency of organic solar cells is to use a tandem architecture consisting of two subcells, so that a broader part of the solar spectrum can be used and the thermalization loss of photon energy can be minimized1. For a tandem cell to work well, it is important for the subcells to have complementary absorption characteristics and generate high and balanced (matched) currents. This requires a rather challenging effort to design and select suitable active materials for use in the subcells. Here, we report a high-performance solution-processed, tandem solar cell based on the small molecules DR3TSBDT and DPPEZnP-TBO, which offer efficient, complementary absorption when used as electron donor materials in the front and rear subcells, respectively. Optimized devices achieve a power conversion efficiency of 12.50% (verified 12.70%), which represents a new level of capability for solution-processed, organic solar cells.

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