Ambient fabrication of perovskite solar cells through delay-deposition technique

Abstract

The establishment of perovskite solar cells (PSCs) in terms of their power-conversion efficiency (PCE) over silicon-based solar cells is undeniable. The state-of-art of easy device fabrications of PSCs has enabled them to rapidly gain a place in third-generation photovoltaic technology. Numerous obstacles remain to be addressed in device efficiency and stability. Low performance owing to easily degraded surface and deterioration of perovskite film quality resulting from humidity are issues that often arise. This work explored a new approach to producing high-quality perovskite films prepared under high relative humidity (RH = 40%–50%). In particular, the ubiquitous 4-tert-butylpyridine (tBp) was introduced into lead iodide (PbI2) precursor as an additive, and the films were fabricated using a two-step deposition method followed by a delay-deposition technique of methylammonium iodide (MAI). High crystallinity and controlled nucleation of MAI were needed, and this approach revealed the significance of time control to ensure high-quality films with large grain size, high crystallography, wide coverage on substrate, and precise and evenly coupled MAI molecules to PbI2 films. Compared with the two-step method without time delay, a noticeable improvement in PCE from 3.2 to 8.3% was achieved for the sample prepared with 15 s time delay. This finding was primarily due to the significant enhancement in the open-circuit voltage, short-circuit current, and fill factor of the device. This strategy can effectively improve the morphology and crystallinity of perovskite films, as well as reduce the recombination of photogenerated carriers and increase of current density of devices, thereby achieving improved photovoltaic performance.