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.

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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

A copper-doped nickel oxide bilayer for enhancing efficiency and stability of hysteresis-free inverted mesoporous perovskite solar cells

A series of cyano-containing distyrylbenzenes were synthesized as the model compounds to systematically study the effect of cyano substituents on the redox behaviors of conjugated molecules. By introducing the electron-withdrawing functional groups (cyano and dicyanovinyl) onto the phenylene ring, both electron affinity and electrochemical stability of the resulting distyrylbenzenes are greatly enhanced. The results enabled us to design and synthesize a new class of highly electron affinitive, fluorene-based copolymers with these cyano-containing chromophores as comonomers. The effects of acceptor strength and side chain on electron-transporting properties of these polymers were also investigated. By properly adjusting copolymer compositions, a combined high electron affinity and transport was achieved in a statistic copolymer, poly(fluorenebenzothiadiazole−cyanophenylenevinylene) (PFB−CNPV). An external quantum efficiency up to 0.88% and brightness as high as 4730 cd/m2 were achieved in a double-layer li...

Effect of Cyano Substituents on Electron Affinity and Electron-Transporting Properties of Conjugated Polymers

We design and fabricate a 320 nm slot for an electro-optic (E-O) polymer infiltrated silicon photonic crystal waveguide. Because of the large slot width, the poling efficiency of the infiltrated E-O polymer (AJCKL1/amorphous polycarbonate) is significantly improved. When coupled with the slow light effect from the silicon photonic crystal waveguide, an effective in-device r33 of 735 pm/V, which to our knowledge is a record high, is demonstrated, which is ten times higher than the E-O coefficient achieved in thin film material. Because of this ultrahigh E-O efficiency, the VπL of the device is only 0.44 V mm, which is to our knowledge the best result of all E-O polymer modulators.

Alex K.-Y. Jen

Papers

A copper-doped nickel oxide bilayer for enhancing efficiency and stability of hysteresis-free inverted mesoporous perovskite solar cells

Effect of Cyano Substituents on Electron Affinity and Electron-Transporting Properties of Conjugated Polymers

Effective in-device r_33 of 735 pm/V on electro-optic polymer infiltrated silicon photonic crystal slot waveguides

Facile approach to nonlinear optical side-chain aromatic polyimides with large second-order nonlinearity and thermal stability

A Conjugated, Neutral Surfactant as Electron‐Injection Material for High‐Efficiency Polymer Light‐Emitting Diodes