A positive correlation between local photocurrent and grain size in a perovskite solar cell

A positive correlation between the local photocurrent and grain size is found in the perovskite solar cell, and the optimum grain size is ≥2 μm. Developing an interplay between the local morphological character and its local photovoltaic (PV) parameters in a perovskite thin film is essential for guiding the construction of highly-efficient perovskite solar cells (PSCs). To achieve a higher PSC performance, great efforts have been devoted to the growth of larger perovskite grains; however, how the gain size can influence the PSC performance in a working device remains unclear. Herein, using laser-scanned confocal microscopy coupled with a photocurrent detection module, we realize local photocurrent, photoluminescence (PL) intensity and PL lifetime mappings directly in a working PSC. For perovskite grains of various sizes (from ∼500 nm to a few micrometers), their local photocurrent exhibit a statically positive correlation with the grain size, but anti-correlated with the grain’s local PL intensity. This result suggests that a larger perovskite grain likely has fewer defects and more importantly better interfacial contact with the charge collection layers and thus leads to higher charge collection efficiency, and the optimum grain size is found to be ≥2 μm. Our result provides important guidance to the growth and control of perovskite microstructures toward the further improvement of PSC performance.