ALD Al2O3 on hybrid perovskite solar cells: Unveiling the growth mechanism and long-term stability

Though perovskite solar cells (PSC) have reached high efficiency comparable to its counterparts, it is still striving towards finding a strong hold in terms of long-term stability. Several approaches have been made to prevent the degradation of PSC. Here, we present low-temperature ALD deposited Al2O3 as an effective encapsulant for PSC. The encapsulated devices improve with PCE reaching up to 19.4% post 300 cycles of Al2O3 deposition. In-situ QCM and FTIR measurements reveal that trimethylaluminum gets trapped inside the spiro-OMeTAD layer and is available for the subsequent dosage of H2O during nucleation regime. Here we unveil the fact that the ALD grown Al2O3 is not only surface limited, but the material penetrates the spiro-OMeTAD and enhances the hole transport property, improving the overall performance of encapsulated cells. Intermittent measurements indicate that encapsulated cells are stable, retaining 84% of its initial efficiency by the end of 300 days. Subsequently we elucidate that the device measurements under continuous illumination and with different bias conditions and atmosphere show that the ALD grown encapsulation prevents ingress of moisture and oxygen into the cells maintaining their stability.