Anomalous Photovoltaic Response in CH3NH3PbBr3 – Dr. Wenge Yang
AUGUST 15, 2015
The performance of solar cell new comer materials called halide pervoskite has soared in recent years, which has rapidly surpassed that of both conventional dye-sensitized and organic photovoltaics. A recent research from a team of scientists including HPSTAR scientists Dr. Wenge Yang, Dr. Liuxiang Yang, Xiangting Ren and Dr. Lin Wang, using in situ high-pressure techniques to investigate the photovoltaic properties of organolead bromide perovskite CH3NH3PbBr3, found anomalous photovoltaic response associated with the pressure-induced phase transitions and reversible amorphization.
Solar energy is the largest noncarbon-based energy source. As opposed to more conventional resources such as coal and fossil fuels, solar energy can serve as a means to solving the serious issue of global warming that has arisen from the evolution of CO2. The use of solar cells is an effective method of converting solar energy into electric energy, and it represents a very interesting research challenge. A new breed of materials for solar cells with long-term durable solid-state perovskites burst into the limelight in 2012, which are cheap, easy to make, and already capable of converting ~20% of the energy in sunlight to electricity by today. Solution-processable organic–inorganic hybrid perovskites—such as CH3NH3PbX3(X = Cl, Br, I) — have attracted growing attention as light - harvesting materials for mesoscopic solar cells due to their unique optical properties, excitonic properties, and electrical conductivity. The superb photovoltaic performances of the perovskite solar-cell materials are attributed to the combination of useful properties, such as excellent charge-carrier mobility from inorganic metal-halide octahedral building blocks and their plastic mechanical properties introduced by the organic parts.
By a serials of measurements including in-situ high pressure X-ray diffraction, photoluminescence, electrical resistance, photocurrent measurements combined with theoretical simulations, the team systematically studied the pressure effect on the crystal structure and photovoltaic performance of organoleadbromide perovskite CH3NH3PbBr3 (MAPbBr3). Two phase transformations followed by a reversible amorphization were observed during compression and decompression at room temperature. Band-gap evolution of MAPbBr3 derived from photoluminescence measurement shows anomalous behavior with red-shift followed by blue-shift which is due to the competition between compression effect and pressure-induced amorphization. Despite the highly increased electrical resistance under high pressure, the material maintains its semiconductor characteristics and considerable response to the visible light irradiation.
Based on the experimental results and theoretical calculations, the researchers concluded that high pressure was also a powerful technique for material design towards novel functionalities. The future exploration considering amorphous organometal salts with comparable or even better performance than their crystalline form may greatly drive the development of perovskite-sensitized solar cells.
“Our results not only show that hydrostatic pressure may provide an applicable tool for the organohalide perovskites based photovoltaic device functioning as switcher or controller, but also shed light on the exploration of more amorphous organometal composites as potential light absorber,” said Dr. Wang, the leading author of this publication.
The work is published in J. Am. Chem. Soc. DOI:10.1021/jacs.5b06346.
Caption: Pressure effect on the structure, bandgap and photocurrent of CH3NH3PbBr3.