Multiphosphorylated molecules for buried interface regulation of inverted perovskite solar cells in a two-step process

Abstract

Insufficient coverage of self-assembled monolayers (SAMs) and inadequate control of the buried interface of perovskites still limit the performance of perovskite solar cells (PSCs). Herein, a strategy of reinforcing SAMs and managing perovskite buried interface is reported by using ethylenediamine tetramethylene phosphonic acid (EAPA) to address above challenges. First, the EAPA solution washes away the unbound or weakly bound Me-4PACz molecules from NiO_x and fills the SAM gaps to achieve a high-coverage and uniformly distributed SAM layer. Force-field molecular dynamics simulations further confirm the superior coverage on the corrugated NiO_x surface. Second, EAPA delays the chemical reaction of the two-step process by interacting with perovskite components, promoting the conversion of lead iodide (PbI₂) into perovskite and flattening grain boundaries at the buried interface. This process homogenizes and relieves interfacial stress while passivating defects, thereby significantly suppressing non-radiative recombination. Consequently, we obtain PSCs with a power conversion efficiency of 26.27% and a high open-circuit photovoltage of 1.209 V using a two-step method. The inverted PSCs show excellent operational stability, retaining 90% of the initial efficiency after 800 h of continuous light soaking under MPPT at 65 °C. This work provides a promising strategy for simultaneously improving the stability and efficiency of inverted PSCs.