Inverted perovskite solar cells via multifunctional potassium sorbate to etch PEDOT:PSS and modify the PEDOT:PSS/perovskite interface

Abstract

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been widely used as a hole transport layer in inverted perovskite solar cells (PSCs). However, the PSS chains on the surface of PEDOT:PSS can absorb water molecules in humid environments, which accelerates the degradation of the perovskite at the PEDOT:PSS/perovskite interface (hereafter referred to as the PP interface). In addition, the mismatched valence band levels between PEDOT:PSS and perovskite result in a high defect density at the PP interface, leading to significant open-circuit voltage loss. To address these issues, inspired by semiconductor etching processes, we employed an ethanol solution of potassium sorbate to etch the surface of PEDOT:PSS. After etching with ethanol, the sorbate anion and potassium ions from potassium sorbate fill the positions left by the etched PEDOT and PSS chains, forming new electrostatic interactions. This not only improves the conductivity of PEDOT:PSS but also improves the energy level matching between PEDOT:PSS and perovskite, facilitating hole transport at the PP interface. As a result, the open-circuit voltage of the device increased from 1.085 to 1.144 V, and the power conversion efficiency improved from 17.54% to 21.10%. The –C=O group of potassium sorbate also acts as a Lewis base, forming a Lewis adduct with the uncoordinated Pb2+ ions at the PP interface, significantly reducing the defect density and enhancing the stability of the PSCs. This approach provides new insights and methods for improving both the efficiency and stability of inverted PSCs.