Interfacial Degradation due to Unbalanced Charge Extraction in Perovskite Photovoltaics.

Perovskite photovoltaics are plagued by low stability, and achieving stable devices requires eliminating every possible source of defects. One such source is photoinduced degradation during device fabrication if incomplete devices are not kept in the dark during preparation, transfer, or storage. After perovskite deposition but before addition of the upper layers, the degradation of the incomplete devices upon illumination is caused by unbalanced charge extraction and the electric field they produce at the buried interface. This phenomenon is becoming more crucial, as passivation is now also required for the buried interface, but the passivants can be more prone to damage by the unbalanced charge extraction than the perovskite itself. Herein, we demonstrate a buried interface passivant that improves the efficiency and stability of the complete device but is highly unstable in incomplete devices. The degradation of the passivant triggers phase segregation in the perovskite itself, leading to rapid nonradiative charge recombination at the interface. The case exemplifies how slow, or blocked, electron extraction can manifest as degradation on the hole transfer side, and it is important to minimize light exposure during device preparation.