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.

/pdf/electron-hole-diffusion-lengths-exceeding-1-micrometer-in-an-3rhimkkmrj.pdf

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

https://absimage.aps.org/image/MAR14/MWS_MAR14-2013-000770.pdf

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

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.

http://science.sciencemag.org/content/sci/345/6196/542.full.pdf

Interface engineering of highly efficient perovskite solar cells

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

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

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%.

/pdf/high-performance-photovoltaic-perovskite-layers-fabricated-13hmgypipo.pdf

High-performance photovoltaic perovskite layers fabricated through intramolecular exchange

Novel conjugated light-emitting polymers were synthesized via a Wittig-Horner condensation reaction between a binaphthyl dicarbaldehyde and a series of electron-rich or electron-deficient aryl diphosphonates. After comparing these materials with the model compound, 4c, it was revealed that the introduction of a twisted, non-coplanar binaphthyl structure provided an effective approach for tailoring the spectral characteristics of the polymers and improving their solubility and thermal stability (glass transition temperature, Tg, 〉200°C). Furthermore, the band structures of the polymers could be fine-tuned by changing the electronic properties of the bridging aromatic units. The electroluninescence (EL) and device characteristics were also reported in this paper.

Poly(Binaphthalenevinylene- alt -Phenylenevinylene) Derivatives: Novel Luminescent Polymers for Light-Emitting Devices

https://spie.org/StudentChapterReports/UW_Report_200512.pdf

Our members were authors and coauthors of several papers

Inverted (p‐i‐n) perovskite solar cells have drawn great attention due to their outstanding stability and low‐temperature processibility. However, their power conversion efficiency (PCE) still lags behind conventional (n‐i‐p) devices mainly due to the lack of strategies to stabilize α‐FAPbI3 without changing the bandgap. In this work, a facile and effective strategy is reported to regulate the residual strain via pseudo halide‐based ionic liquids incorporation to stabilize α‐FAPbI3 perovskite in inverted perovskite solar cells (PVSCs). The employment of methylamine formate (MAFa) ionic liquid enables a homogenously stronger compressive strain to restrain the transition of shared‐corner PbI6 octahedron into shared‐face δ‐FAPbI3, as well as affecting the dynamic behavior of carriers and defects to achieve a record PCE (24.08%) among the reported inverted FAPbI3 perovskite solar cells up to now. In addition, the MAFa incorporation results in enhanced device stability, unencapsulated PVSC retains over 90% of its initial efficiency after stored in ambient environment (RH:30 ± 5%) for 1000 h. This work provides an efficient strategy to realize efficient and stable α‐FAPbI3 based inverted PVSCs to further catch up with the conventional ones.

Strain Regulation via Pseudo Halide‐Based Ionic Liquid toward Efficient and Stable α‐FAPbI3 Inverted Perovskite Solar Cells

Tailoring the Quantum Well Structure and Distribution of Reduced-Dimensional Perovskites for Charge Dynamics Optimization

We propose and demonstrate a novel electro-optic (EO) polymer/TiO2 multilayer slot waveguide modulator for optical interconnections.

Alex K.-Y. Jen

Papers

Poly(Binaphthalenevinylene- alt -Phenylenevinylene) Derivatives: Novel Luminescent Polymers for Light-Emitting Devices

Our members were authors and coauthors of several papers

Strain Regulation via Pseudo Halide‐Based Ionic Liquid toward Efficient and Stable α‐FAPbI3 Inverted Perovskite Solar Cells

Tailoring the Quantum Well Structure and Distribution of Reduced-Dimensional Perovskites for Charge Dynamics Optimization

Electro-Optic Polymer/TiO2 Multilayer Slot Waveguide Modulators for Optical Interconnections