Amorphous TiO2 Coatings Stabilize Perovskite Solar Cells

Significant progress has been achieved in improving the power conversion efficiency (PCE) of perovskite solar cells (PSCs) for a decade, but the long-term stability is still underdeveloped. In a regular PSC structure, 2,2′,7,7′-tetrakis­(N,N-di-p-methoxyphenylamine)­9,9′-spirobifluorene (Spiro-OMeTAD) with Li additives and metal electrodes are widely adopted, which leads to facile degradation under device operating conditions because of ion migration. Herein, we show an interface-engineered stabilization approach to prevent ion migration in PSCs enabled by amorphous (a)-TiO2 capable of hole transfer grown by atomic layer deposition (ALD). This layer prevents ion migration of Li additives with consequent aggregation as well as metal electrode diffusion into the perovskite layer. Furthermore, the combined layers of Spiro-OMeTAD/a-TiO2 unprecedentedly promote device efficiency, which is further verified with other organic hole transport layers. Finally, the operational stability of the TiO2-PSC is substantially improved in comparison to that of the control PSC.