Using Pressure to Optimize Perovskite Solar Cells

Figure: Moving clockwise from top left, pressure cycling (purple arrows) of an organotin halide-based perovskite solar cell leads to a conductivity increase of over 300% (center), and repeated pressure cycling (green arrows) demonstrates enhanced structural stability of the pressure-treated material.
Figure: Moving clockwise from top left, pressure cycling (purple arrows) of an organotin halide-based perovskite solar cell leads to a conductivity increase of over 300% (center), and repeated pressure cycling (green arrows) demonstrates enhanced structural stability of the pressure-treated material.

Perovskite solar cells (PSCs) have attracted much attention owing to their high power conversion efficiency and low manufacturing cost.  Power conversion efficiencies of over 20% have recently been achieved with lead-based organic-inorganic halide PSCs, but these have relatively low structural stability, and the use of lead in the manufacturing process introduces problems of toxicity.  Recently, organotin perovskites have been synthesized as lead-free alternatives, and a number of chemical and processing modifications have been applied to these compounds in an effort to tune their crystal structure and electronic properties, with the hope of yielding more stable compounds which exhibit superior absorption and conductivity.

Using high pressure as a tool for crystal structure modification, researchers recently carried out x-ray diffraction measurements on organotin PSCs at HPCAT.  Through pressure cycling the PSC undergoes pressure-induced amorphization followed by recrystallization.  Complementary electronic transport measurements reveal the recovered low pressure phase exhibits an increase in conductivity of over 300%, and repeated pressure cycling demonstrates increased structural stability.  The enhanced structural stability and electronic properties may be due in part to more uniform grain size and orientation which cannot be achieved through normal synthetic processes.  The details of this work have recently been published by Lü and coworkers in Advanced Materials: DOI: 10.1002/adma.201600771