Alex K.-Y. Jen

Bio: Alex K.-Y. Jen is an academic researcher from City University of Hong Kong. The author has contributed to research in topics: Perovskite (structure) & Polymer solar cell. The author has an hindex of 128, co-authored 921 publications receiving 61811 citations. Previous affiliations of Alex K.-Y. Jen include University of Nebraska–Lincoln & Zhejiang California International NanoSystems Institute.

Metal grid/conducting polymer hybrid transparent electrode for inverted polymer solar cells

Abstract: A simple method was developed using metal grid/conducting polymer hybrid transparent electrode to replace indium tin oxide (ITO) for the fabrication of inverted structure polymer solar cells. The performance of the devices could be tuned easily by varying the width and separation of the metal grids. By combining the appropriate metal grid geometry with a thin conductive polymer layer, substrates with comparable transparency and sheet resistance to those of ITO could be achieved. Polymer solar cells fabricated using this hybrid electrode show efficiencies as high as ∼3.2%. This method provides a feasible way for fabricating low-cost, large-area organic solar cells.

Stable Low‐Bandgap Pb–Sn Binary Perovskites for Tandem Solar Cells

Abstract: A low-bandgap (1.33 eV) Sn-based MA0.5 FA0.5 Pb0.75 Sn0.25 I3 perovskite is developed via combined compositional, process, and interfacial engineering. It can deliver a high power conversion efficiency (PCE) of 14.19%. Finally, a four-terminal all-perovskite tandem solar cell is demonstrated by combining this low-bandgap cell with a semitransparent MAPbI3 cell to achieve a high efficiency of 19.08%.

CuGaO2: A Promising Inorganic Hole-Transporting Material for Highly Efficient and Stable Perovskite Solar Cells

Abstract: The p-type inorganic semiconductor CuGaO2 as a hole-transporting layer (HTL) in perovskite solar cells (PSCs) provides higher carrier mobility, better-energy level matching, and superior stability, as well as low-temperature processing technique. Compared to organic HTL, a very competitive PCE of 18.51% with long-term stability is achieved. This indicates that CuGaO2 is a promising HTL for efficient and stable PSCs.

Roles of Fullerene-Based Interlayers in Enhancing the Performance of Organometal Perovskite Thin-Film Solar Cells

Abstract: To surmount these obstacles, conventional PHJ PVSCs with the confi guration of substrate/HTL (p)/perovskite (i)/fullerene derivative (n) has been developed. [ 9 ] PEDOT:PSS or NiO X are the commonly employed HTLs to date while the electron-transporting layers (ETLs) employed are mainly based on fullerene derivatives. [ 7c,9c,d,10 ] It is worth noting that room temperature and orthogonal solvent processability of fullerene derivatives can successfully prevent the degradation of the underlying perovskite layer. In addition, the decent electron mobility of most fullerene derivatives makes them promising ETLs for high-performance PVSCs. Guo et al. fi rst demonstrated the feasibility of such a conventional PHJ confi guration, realizing a PCE of 3.9% by employing a phenyl-C 61 -butyric acid methyl ester (PC 61 BM) ETL. [ 9c ] Although three different fullerene derivatives (C 60 , PC 61 BM, and indene-C 60 bisadduct (IC 60 BA)) were investigated as ETLs, the functions of these fullerene-based interlayers were not fairly explored due to the inferior quality of the perovskite thin fi lm grown atop them. Soon after, a PC 61 BM ETL was used in a similar PHJ structure by Lam et al. to further improve the device performance to 7.4% by optimizing the perovskite precursor solution concentration and the blending ratio of PbI 2 and methylammonium iodide (MAI). [ 9a ] Lately, Jen and co-workers have signifi cantly enhanced the PCE to 12%–13%, respectively, by optimizing perovskite deposition either by controlling annealing conditions or adding a solvent additive.[11] Most recently, Seok and co-workers have reported an over 14% PCE through solvent engineering and thickness optimization of PC 61 BM. [ 12 ]

High‐Performance Fully Printable Perovskite Solar Cells via Blade‐Coating Technique under the Ambient Condition

Abstract: In order to fabricate large-area PVSCs, one of the critical challenges is to understand the infl uence of ambient environment on resultant perovskite thin-fi lms since perovskite crystals are sensitive to humidity under ambient condition. It has been shown that perovskite crystals degrade gradually when they are in contact with ambient moisture for certain time. [ 31,32 ] Therefore, most of the high performance perovskite solar cells are prepared in glovebox to avoid contacting moisture. However, fabricating PVSCs under ambient condition is inevitable if we desire to transition from laboratory research into large-scale applications. Lately, there are several encouraging reports about allowing limited amount of moisture to facilitate the perovskite crystallization and improve the performance of resulting device. [ 33,34 ] However, there are no detailed underlying mechanisms explained on how moisture affects perovskite crystallization so far. To alleviate these problems, we have investigated the feasibility of achieving fully printable PVSCs by the blade-coating technique under the ambient condition. The blade-coating fabrication has been widely used to fabricate OSCs and is proven to be a simple, environment-friendly, and low-cost method for the solution-processed photovoltaic. Compared to the screen printing, it not only can print nanoparticles, but also can print all kinds of solutions with any concentration. Moreover, the fi lm morphology control of the blade-coating method is much better than the spray coating and roll-to-roll printing; high-quality photoactive layers with controllable thickness can be accomplished by using a precisely translational blade under the ambient condition with controlled relative humidity. The PVSCs with a confi guration of ITO/poly(3,4-ethylenedioxy-thiophene):poly(4-styrenesulfonate) (PEDOT:PSS)/ CH 3 NH 3 PbI X Cl 3− X /[6,6]-phenyl-C 61 butyric acid methyl ester (PC 61 BM)/Bis-C 60 /Ag were fabricated to realize the fully printable process, as illustrated in Figure 1 a. All constituent interlayers, except for the Ag top electrode, were prepared via blade-coating. The coating conditions were optimized to allow the preparation of high-quality interlayer fi lms. Especially, the effect of humidity was carefully investigated and monitored to facilitate the crystallization of perovskite fi lms under ambient condition. Finally, high PCE (10.44% ± 0.23%) device could be achieved after optimizing the blade-coating process and relative humidity in environment. Moreover, a high-performance fl exible PVSC with a PCE of 7.14% ± 0.31% was demonstrated for the fi rst time using this low-temperature (<150 °C) fully printable process. The exceptional photovoltaic properties demonstrated recently for organic–inorganic halide perovskites (such as CH 3 NH 3 PbX 3 (X = Cl, Br, or I)) have attracted great attention from researchers. [ 1–8 ] The promising features of these perovskites include broad and intense absorption spectra, [ 9 ] appropriate semiconducting properties, [ 10 ] long carrier diffusion length, [ 11,12 ]

Electron-hole diffusion lengths exceeding 1 micrometer in an organometal trihalide perovskite absorber.

Abstract: Organic-inorganic perovskites have shown promise as high-performance absorbers in solar cells, first as a coating on a mesoporous metal oxide scaffold and more recently as a solid layer in planar heterojunction architectures. Here, we report transient absorption and photoluminescence-quenching measurements to determine the electron-hole diffusion lengths, diffusion constants, and lifetimes in mixed halide (CH3NH3PbI(3-x)Cl(x)) and triiodide (CH3NH3PbI3) perovskite absorbers. We found that the diffusion lengths are greater than 1 micrometer in the mixed halide perovskite, which is an order of magnitude greater than the absorption depth. In contrast, the triiodide absorber has electron-hole diffusion lengths of ~100 nanometers. These results justify the high efficiency of planar heterojunction perovskite solar cells and identify a critical parameter to optimize for future perovskite absorber development.

Electron-Hole Diffusion Lengths Exceeding 1 Micrometer in an Organometal Trihalide Perovskite Absorber

Abstract: Organic-inorganic perovskites have shown promise as high-performance absorbers in solar cells, first as a coating on a mesoporous metal oxide scaffold and more recently as a solid layer in planar heterojunction architectures. Here, we report transient absorption and photoluminescence-quenching measurements to determine the electron-hole diffusion lengths, diffusion constants, and lifetimes in mixed halide (CH3NH3PbI(3-x)Cl(x)) and triiodide (CH3NH3PbI3) perovskite absorbers. We found that the diffusion lengths are greater than 1 micrometer in the mixed halide perovskite, which is an order of magnitude greater than the absorption depth. In contrast, the triiodide absorber has electron-hole diffusion lengths of ~100 nanometers. These results justify the high efficiency of planar heterojunction perovskite solar cells and identify a critical parameter to optimize for future perovskite absorber development.

Interface engineering of highly efficient perovskite solar cells

Abstract: Advancing perovskite solar cell technologies toward their theoretical power conversion efficiency (PCE) requires delicate control over the carrier dynamics throughout the entire device. By controlling the formation of the perovskite layer and careful choices of other materials, we suppressed carrier recombination in the absorber, facilitated carrier injection into the carrier transport layers, and maintained good carrier extraction at the electrodes. When measured via reverse bias scan, cell PCE is typically boosted to 16.6% on average, with the highest efficiency of ~19.3% in a planar geometry without antireflective coating. The fabrication of our perovskite solar cells was conducted in air and from solution at low temperatures, which should simplify manufacturing of large-area perovskite devices that are inexpensive and perform at high levels.

Aggregation-Induced Emission: Together We Shine, United We Soar!

Abstract: Ju Mei,†,‡,∥ Nelson L. C. Leung,†,‡,∥ Ryan T. K. Kwok,†,‡ Jacky W. Y. Lam,†,‡ and Ben Zhong Tang*,†,‡,§ †HKUST-Shenzhen Research Institute, Hi-Tech Park, Nanshan, Shenzhen 518057, China ‡Department of Chemistry, HKUST Jockey Club Institute for Advanced Study, Institute of Molecular Functional Materials, Division of Biomedical Engineering, State Key Laboratory of Molecular Neuroscience, Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China Guangdong Innovative Research Team, SCUT-HKUST Joint Research Laboratory, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China

High-performance photovoltaic perovskite layers fabricated through intramolecular exchange

Abstract: The band gap of formamidinium lead iodide (FAPbI3) perovskites allows broader absorption of the solar spectrum relative to conventional methylammonium lead iodide (MAPbI3). Because the optoelectronic properties of perovskite films are closely related to film quality, deposition of dense and uniform films is crucial for fabricating high-performance perovskite solar cells (PSCs). We report an approach for depositing high-quality FAPbI3 films, involving FAPbI3 crystallization by the direct intramolecular exchange of dimethylsulfoxide (DMSO) molecules intercalated in PbI2 with formamidinium iodide. This process produces FAPbI3 films with (111)-preferred crystallographic orientation, large-grained dense microstructures, and flat surfaces without residual PbI2. Using films prepared by this technique, we fabricated FAPbI3-based PSCs with maximum power conversion efficiency greater than 20%.