The effects of selectively blocking the electron transport layer of n-i-p perovskite solar cells with polymer particles on device performance

Perovskite solar cells (PSCs) continue to attract considerable academic and industrial interest due to their excellent potential to contribute to solar energy generation. The application of PSCs will benefit from improvements in the understanding of the roles of the interfaces present in charge transport and recombination. The buried perovskite/electron transport layer (ETL) interface in n-i-p PSCs is relatively difficult to study, particularly when molecular additives are used to target that region because they are not able to be visualized by electron microscopy. Here, we use sub-micrometer insulating polystyrene microgel particles (PS MGs) to partially cover the ETL of PSCs. The MGs provide well-defined colloidal additives for selectively covering the ETL because they are laterally constrained and the coverage is readily tuneable. We examine the effect of MG concentration on the device performance and find that the MGs passivate the SnO₂ ETL and obstruct charge transport. We then engineer gaps between the deposited MGs using UV/ozone treatment and achieve a maximum power conversion efficiency (PCE) of 20.09% compared to 19.60% for the control. Remarkably, the PSCs can still function efficiently even when the ETL is mostly covered by the MGs. We show that the most efficient devices have partially covered ETLs with a lateral blocking distance of ~ 500 nm. This work demonstrates that mostly covering the ETL with insulating particles does not necessarily lead to a catastrophic decrease in performance. In contrast, this study provides a new scalable method for improving the PCE and for potentially enhancing light management for PSCs in the future.