Curtailing Non-Radiative Recombination and Tailoring Interfacial Energetics via Bimolecular Passivation toward Efficient Inverted Perovskite Solar Cells

Despite significant development of perovskite solar cells (PSCs) in recent years, presence of nonradiative recombination centers at the perovskite surface, grain boundaries, and interfaces remain a major bottleneck in achieving the desired device performance. Also, energy levels offset among perovskite and neighboring functional layers leads to poor charge extraction, thereby further limiting the device capability. Therefore, it is essential to carefully understand the underlying defects and develop a suitable passivation technique to suppress such detrimental imperfections. Herein, we propose a synergistic bimolecular passivation strategy to simultaneously reduce the trap states density, enhance crystallinity and improve interfacial charge transfer in inverted (p-i-n) PSCs. The poly(2-ethyl-2-oxazoline) (PEOXA) introduced in the antisolvent modulates the crystallization kinetics and concurrently passivates the grain boundaries and surface defects of perovskite films. In addition, a simple surface post-treatment of the perovskite layer using 3-(aminomethyl)pyridine (3-APy) suppresses contact-induced interfacial recombination as a consequence of lowered work function in the surface region. This synergistic passivation approach renders enhanced defect passivation and improved interfacial energetics, leading to a significant suppression in undesirable nonradiative recombinations and improvement of interfacial charge transfer. Consequently, the power conversion efficiency (PCE) of the devices significantly improves from 22.01 to 24.65% (with a certified PCE of 24.01%), while the operational stability at the maximum power point is maintained at a decent value for over 1000 h of continuous illumination. This work provides a guideline for developing multimolecular passivation approaches to selectively target various defects toward improved performance of perovskite optoelectronic devices.