Constructing an n/n+ homojunction in a monolithic perovskite film for boosting charge collection in inverted perovskite photovoltaics

The suboptimal carrier dynamics at the perovskite/electron transport layer has largely limited the further performance enhancement of the state-of-the-art inverted p-i-n structured perovskite solar cells. Herein, we discovered that a simple surface modification of the perovskite film by a trivalent metal halide salt, InBr3, could convert the doping levels of the top surface to be more n-type, which spontaneously formed an intriguing n/n(+) homojunction between the bulk (weak n type (n) component) and the surface (more n-type (n(+)) component) in a monolithic perovskite film. This brought about synergistic advantages of the enlarged built-in electric field for facilitated charge separation, as well as optimized electronic energy level alignment and minimized electron injection barrier at the perovskite/C-60 interface, leading to both accelerated charge extraction and suppressed interfacial charge recombination. Blade-coated inverted PSCs with n/n(+) homojunctions achieved a high power conversion efficiency (PCE) of up to 22.2%, narrowing the efficiency gap with their conventional n-i-p counterparts. The InBr3 surface treatment also improved the operational stability to >1000 hours under light with 93% initial efficiency retained.

Automated summary

A surface modification of the perovskite film with InBr3 salt led to the formation of an n/n(+) homojunction, enhancing both the performance and operational stability of the inverted perovskite solar cells. This strategy narrowed the efficiency gap with conventional counterparts and improved efficiency retention over 1000 hours of operation.