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

We demonstrate a ring-resonator modulator based on a silicon-polymer hybrid slot waveguide with a tunability of 127 pm/V at RF speeds and a bandwidth of 1 GHz, for optical wavelengths near 1550 nm Our slot waveguides were fabricated with 193 nm optical lithography, as opposed to the electron beam lithography used for previous results The tunability is comparable to some of the best ring-based modulators making use of the plasma dispersion effect The speed is likely limited only by resistance in the strip-loading section, and it should be possible to realize significant improvement with improved processing

Silicon-polymer hybrid slot waveguide ring-resonator modulator.

Diels−Alder “Click Chemistry” for Highly Efficient Electrooptic Polymers

ITO-free polymer solar cells with efficiencies as high as 6.6% and 5.8% are fabricated on glass and polyethylene naphthalate (PEN) by using TeO(2) to enhance the in-coupling of light in an Ag-Ag microcavity. These cells exhibit higher performance, selective microcavity resonance as a function of the thickness of TeO(2) , and better bending stability than flexible devices made with ITO.

Optical design of transparent thin metal electrodes to enhance in-coupling and trapping of light in flexible polymer solar cells.

Design, Synthesis, and Properties of Highly Efficient Side‐Chain Dendronized Nonlinear Optical Polymers for Electro‐Optics

We explore the effects of nonradiative recombination at the extracting contacts on the achievable performance of halide perovskite photovoltaic cells. First, we perform device simulations using standard drift-diffusion models with experimental semiconductor parameters matching those of methylammonium lead triiodide (MAPbI3). We quantify the range of surface recombination velocities (SRVs) that would allow this archetypal perovskite to reach power conversion efficiencies of 27%. In particular, for contacts with well-aligned energy levels, SRVs of ∼1–10 cm/s should enable open-circuit voltages of 1.30 V, within 96% of the Shockley–Queisser limit. Next, we use time-resolved photoluminescence to experimentally determine the SRVs on 14 different common electron- and hole-extracting contacts, including TiO2, SnO2, ZnO, PCBM, ITIC, ICBA, TPBi, PEDOT:PSS, PTAA, PVK, NiO, MoO3, WO3, and spiro-OMeTAD. These results point the way to the selection and rational engineering of better contacts as a means to achieve high...

Alex K.-Y. Jen

Papers

Silicon-polymer hybrid slot waveguide ring-resonator modulator.

Diels−Alder “Click Chemistry” for Highly Efficient Electrooptic Polymers

Optical design of transparent thin metal electrodes to enhance in-coupling and trapping of light in flexible polymer solar cells.

Design, Synthesis, and Properties of Highly Efficient Side‐Chain Dendronized Nonlinear Optical Polymers for Electro‐Optics

Reducing Surface Recombination Velocities at the Electrical Contacts Will Improve Perovskite Photovoltaics