Metal Oxide Layer Design for Lead Halide Hybrid Perovskitein High Performance Photovoltaics and Optoelectronics

Miyasaka Tsutomu^a

^aGraduate School of Engineering, Toin University of Yokohama, Kurogane-cho 1614, Aoba-ku, Yokohama, 225-8503

Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe September Meeting 2015 (NFM15)

Santiago de Compostela, Spain, 2015 September 6th - 15th

Invited Speaker, Miyasaka Tsutomu, presentation 252
Publication date: 8th June 2015

Organo-lead halide perovskites, represented by CH3NH3PbI3,are characterized as intrinsic semiconductor and photoconductor, which exhibit superior functions in high-voltage photovoltaic power generation and high-gain diode current output in optoelectronics. Power conversion efficiencies (PCE) of 2.2 % (liquid junction cell)[1] and 0.4% (fully solid state cell)[2] on the start of our study has evolved up to 20%by controlled crystallization process for high qualitystructuring of perovskite layers. Our group could optimize simple one-step preparation of CH3NH3PbI3-xClxin ambient air conditions to assemble solar cells capable of PCE over 17% for different structures with and without mesoporous metal oxide layers. Here, Al2O3 as metal oxide exhibits high open-circuit voltage (Voc),1.05-1.10V, maintaining 17.2% PCE[3]. Compact blocking layerof Nb2O5, which has conduction band higher than TiO2, was found to achieve high Voc up to 1.13V [3]. While selection of metal oxide materials can improve Voc by way of electron collection and/or recombination suppression, it also influences on hysteretic I-Vbehavior of the perovskite cell,because metal oxide interfaces can be involved in enhancement of hysteresis due to ferroelectric and/or ionic diffusion [4]. For fabrication of flexible perovskite cells, low temperature process (<120oC) of metal oxide coating also works for mesoporous SnO2 and ZnO without substantial loss in Voc [3]. PCE close to 14% was obtained withCH3NH3PbI3 and ZnO-coated ITO electrode, showing good stability without encapsulation under ambient air. Enormous potential of perovskite-based device in optoelectronic applications was found in development of high sensitivity photodetector and light sensor.Such function of CH3NH3PbI3 is enabled by large photoconductivity which can be switched by weak monochromatic light.Here, the structure of metal oxide layer in junction with perovskite absorber is the key to output large current density. As a photodiode, gain of CH3NH3PbI3-induced photocurrent was found to reach a level on the order of 103 with excellent light-switching function [5]. This performance is compared with Si-based avalanche photodiode. The latter, however, needs high voltage 20-100V while the perovskite-based diode is operated with small voltage of commercial battery, 0.5-0.9V.

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