Reducing nonradiative losses in perovskite solar cells via ester-based Lewis base passivation

Abstract

Suppressing nonradiative recombination induced by surface and grain-boundary defects remains a central challenge for achieving high efficiency and long-term stability in formamidinium lead iodide (FAPbI₃) perovskite solar cells (PSCs). Here, we introduce an ester-functionalized quinquephenyl molecule, Ph₅-(COOCH₃)₆, as an effective molecular passivation agent for FAPbI₃ perovskite films. By systematically tuning the concentration of Ph₅-(COOCH₃)₆ deposited atop the perovskite absorber, we demonstrate pronounced improvements in both optoelectronic quality and device performance. Structural and spectroscopic analyses reveal that Ph₅-(COOCH₃)₆ passivation preserves the crystalline integrity of FAPbI₃ while inducing favorable surface electronic modifications, evidenced by an upward shift in surface potential, reduced energetic disorder, and suppressed trap-assisted recombination. Consequently, Ph₅-(COOCH₃)₆-treated films exhibit prolonged carrier lifetimes, reduced trap densities, and improved charge transport characteristics. Devices incorporating an optimal Ph₅-(COOCH₃)₆ concentration (2 mg mL⁻¹) achieve a champion power conversion efficiency (PCE) of 23.13% with an average efficiency of 22.86 ± 0.19%, accompanied by simultaneous enhancements in all photovoltaic parameters. Moreover, Ph₅-(COOCH₃)₆ passivated PSCs display markedly improved operational stability, retaining ∼94.4% of their initial efficiency after 1000 h of aging without encapsulation, compared to severe degradation in control devices. This work highlights the potential of ester-based π-conjugated molecular passivation as a versatile strategy for addressing stability and efficiency limitations by mitigating open-circuit voltage (V_OC) losses.