Structured crystallization for efficient all-inorganic perovskite solar cells with high phase stability

All-inorganic perovskites suffer from a phase transition from a cubic α-phase to a tetragonal δ-phase in the ambient atmosphere, although they have the advantage of higher thermal stability. Here, we demonstrated that yttrium-induced perovskite crystallization results in significantly improved phase stability of perovskite even under humid air conditions. Yttrium in precursors was found to impede the crystal growth of perovskite film to stabilize the α-phase of a CsPbI2Br phase and was finally incorporated into the CsPbI2Br perovskite lattice. This structural crystallization process induced by yttrium incorporation gave rise to denser compact films with small grains and host lattice rearrangement by partial substitution for Pb. As a result, a 360-fold phase stability improvement was achieved in humid air with 65% RH compared with the reference film. The favorable electronic structure for efficient electron–hole dissociation and carrier transport to the cathode led to a much-enhanced power conversion efficiency (PCE) of 13.25% after yttrium incorporation compared with only 8.46% for the reference cells in humid air. Moreover, yttrium-incorporated perovskite solar cells (PSCs) without encapsulation exhibited superior long-term stability when stored in ambient air with 65% RH, showing nearly no degradation over 14 h.