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

A new class of second order nonlinear optical chromophores resulted from the replacement of the most reactive CN group in tricyanovinylthiophene derivatives with aryl units, have been designed and synthesized. It was shown that these chromophores provide excellent tradeoffs among many relevant properties such as molecular nonlinearity, linear absorption at 830 nm, inherent thermal stability, chemical stability in processing solvents as well as host polymer matrices at high temperatures and attenuation at 830 nm.

New Developments in Thermally and Chemically Stable Nonlinear Optical Chromophores for E-O Device Applications

A new synthetic method is developed to incorporate efficient nonlinear optical chromophores containing thiophene conjugating units and tricyanovinyl acceptors into side-chain polymers. This approach emphasizes the incorporation of the tricyanovinyl groups into the pendant side chains after the desired polymer is formed.

A Synthetic Approach for the Incorporation of Highly Efficient, Thermally Stable Second Order Nonlinear Optical Chromophores Into Side-Chain Polymers

Selenium-fused Y6 derivatives and their derived polymerized small molecule acceptors for efficient organic solar cells

In this work we present the synthesis and characterization of several novel osmium complexes of the form [Os(N-N)2 L-L]2+ 2Ts- or [Os(L-L)2 N-N]2+ 2Ts- designed for organic light emitting device (OLED) applications. In the complex notation N-N represents a derivative of 2,2’-bipyridine or 1,10-phenanthroline and L-L represents a strong π-acid arsine or phosphine ligand. Several counterions have been used and include tosylate, hexafluorophosphate, triflate, heptafluorobutyrate, chloride, bromide, and iodide. The complexes feature 3MLCT emission that ranges from 611–650 nm, which makes them suitable as an emission source for red OLEDs. Phosphorescent quantum yields as high as 45% and emission lifetimes as short as 400 nanoseconds have been reached. The complexes were incorporated into OLED and give off red, orange, yellow, and green electrophosphorescence. Red devices have been created using polyvinylcarb/2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole, polyvinylnapthalene/2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole, and polyfluorene host materials. OLEDs have been created which give brightness up to 3000 cd m-2 and efficiency up to 2.2% at 632 nm emission.

Novel Divalent Osmium Complexes: Synthesis, Characterization, Tuning of Emission, and use in Organic Light Emitting Diodes

Thin-film luminescent sensors were used to measure dissolved oxygen in picoliter volumes for the purpose of monitoring single-cell oxygen consumption rates, and that work served as the motivation for the development of the method described here. A few different platinum porphyrin sensor materials were examined, with all measurements conducted microscopically. By employing convolution theory to understand observed responses, including an unexpected red luminescent emission from an optic, we developed a new, rapid method for the determination of exponential decay lifetime. This new method of long-pulsed luminescence offers substantially improved signal-to-noise ratios for detected signals as long as self-illumination sources are carefully controlled in the experimental set-up.

Alex K.-Y. Jen

Papers

New Developments in Thermally and Chemically Stable Nonlinear Optical Chromophores for E-O Device Applications

A Synthetic Approach for the Incorporation of Highly Efficient, Thermally Stable Second Order Nonlinear Optical Chromophores Into Side-Chain Polymers

Selenium-fused Y6 derivatives and their derived polymerized small molecule acceptors for efficient organic solar cells

Novel Divalent Osmium Complexes: Synthesis, Characterization, Tuning of Emission, and use in Organic Light Emitting Diodes

Long-Pulsed Luminescence for the Measurement of Dissolved Oxygen