Engineering the buried interface in perovskite solar cells via lattice-matched electron transport layer

Modifying the exposed upper surface of perovskite solar cells (PSCs) has greatly contributed to improving their photovoltaic performance. The equally important buried interface (that is, the hidden bottom of perovskite film and the beginning of perovskite film crystallization) is much less studied due to great difficulties in tailoring it. Here we expose the large-area buried interface non-destructively for direct investigation. We find that the disordered beginning of the perovskite film growth deteriorates the buried interface. To address this issue, instead of using a passivator, we synthesize a transparent and conductive oxide perovskite (SrSnO3) to act as the electron transport layer. The high lattice matching enables a more ordered beginning of the growth of halide perovskite on the electron transport layer, avoiding the formation of a deteriorated buried interface. The constructed buried interface exhibits suppressed defects, strain, better crystallinity, reduced ion migration and fewer voids. The best performing PSCs deliver a power conversion efficiency of 25.17%. Moreover, PSCs with an initial power conversion efficiency of 24.4% maintain 90% of the original value after operating for 1,000 h.