Understanding Hole Extraction of Inverted Perovskite Solar Cells.

This paper describes a correlation between charge extraction and energy-level alignment at the interface of polymeric hole transport layers and perovskite active layers. By tailoring the composition of the conjugated backbone of the hole transport material, energy levels between perovskites and hole transport layers are varied. Matching the band alignment at perovskite/hole transport interfaces dramatically improved charge extraction and thus device performance. Time-resolved microwave conductivity measurements, performed to elucidate hole transfer kinetics, suggest that hole transport layer energy levels greatly influence hole extraction efficiency at this interface, a finding that agrees well with device performance metrics. Furthermore, photoluminescence, Mott-Schottky, and space charge limited current measurements support that energy-level alignment between the hole transport layer and perovskite active layer enables more efficient hole extraction and transport at the device interface. The insight surrounding hole extraction in inverted perovskite devices will help design effective hole transport materials, which, in turn, facilitates the production of more efficient solar cells.