Oligomeric Silica-Wrapped Perovskites Enable Synchronous Defect Passivation and Grain Stabilization for Efficient and Stable Perovskite Photovoltaics

Abstract

The intrinsic instability of hybrid perovskite materials induced by trap states that are correlated with the internal dissociation and migration of constituent ions under illumination arises as one major challenge hampering their commercialization, although high efficiency perovskite solar cells (PSCs) have been demonstrated. Here, we report a facile strategy of wrapping perovskite grains within oligomeric silica (OS) matrix in a core-shell geometry, which can effectively passivate the defects at surfaces and grain boundaries and stabilize the grains at nanoscale by blocking both internal and external degradation paths in perovskite thin films. We observe significant reduction of trap density and elongation of carrier recombination lifetime in OS-wrapped perovskite, which leads to an increased efficiency of 21.5% for p-i-n structured PSCs with a decent open circuit voltage of 1.15 V and a fill factor of 0.81. We propose that such performance enhancement occurs due to the passivation of under-coordinated Pb defects via coordination bond between the oxygen atoms (Lewis base sites) of the –OCH2CH3 group in the OS layer with under-coordinated lead ions in the perovskite. Moreover, the OS shells, as a physical barrier, not only can prevent the permeation of external moisture and atmospheric gases, but also suppress the migration and dissociation of constituent ions, which create and deepen the intrinsic defects. This all-round nanoscale grain wrapping leads to remarkable improvement of the operational stability of PSCs, sustaining 80% of the efficiency after “burn-in’ under full sunlight with UV for more than 5200 h with maximum power tracking. Our findings provide an avenue for synchronous defect passivation and grain stabilization to further enhance both the photovoltaic performance and operational stability of PSCs.