Electronic Effect of Self-Assembled Molecules on Buried Interface Recombination in n-i-p Perovskite Solar Cells

Interfacial recombination at the defective buried interface of perovskite solar cells (PSCs) has long been a persistent and formidable challenge. Introducing molecular bridge via self-assembled molecules (SAMs) offers an effective strategy to mitigate this issue, primarily by chemically passivating interfacial defects that cause nonradiative recombination. However, the influence of SAMs on radiative recombination is often overlooked. In this study, two SAMs with similar molecular configurations but distinct electron-donating/-withdrawing characters─3-thiopheneboronic acid (TBA) and 4-pyridineboronic acid (PBA)─are introduced at the buried interface of n-i-p PSCs. Although both SAMs effectively passivate defects, the PSCs based on them exhibit contrasting trends of performance gain and loss for PBA and TBA, respectively. Mechanistic investigations reveal that TBA featuring an electron-donating thiophene group induces n-type doping in the SnO₂ electron transport layer and exacerbates radiative recombination loss, while PBA with the electron-withdrawing pyridine group behaves in an opposite way. These findings highlight the critical role of the electronic effects of SAMs on buried interface recombination beyond their defect passivation function. The trade-off between these two effects is essential for optimizing buried interface engineering through SAMs.