Amorphous TiO₂ Coatings Stabilize Perovskite\nSolar Cells

Abstract

Significant progress\nhas been achieved in improving the power conversion\nefficiency (PCE) of perovskite solar cells (PSCs) for a decade, but\nthe long-term stability is still underdeveloped. In a regular PSC\nstructure, 2,2′,7,7′-tetrakis­(<i>N</i>,<i>N</i>-di-<i>p</i>-methoxyphenylamine)­9,9′-spirobifluorene\n(Spiro-OMeTAD) with Li additives and metal electrodes are widely adopted,\nwhich leads to facile degradation under device operating conditions\nbecause of ion migration. Herein, we show an interface-engineered\nstabilization approach to prevent ion migration in PSCs enabled by\namorphous (<i>a</i>)-TiO₂ capable of hole transfer\ngrown by atomic layer deposition (ALD). This layer prevents ion migration\nof Li additives with consequent aggregation as well as metal electrode\ndiffusion into the perovskite layer. Furthermore, the combined layers\nof Spiro-OMeTAD/<i>a</i>-TiO₂ unprecedentedly\npromote device efficiency, which is further verified with other organic\nhole transport layers. Finally, the operational stability of the TiO₂-PSC is substantially improved in comparison to that of the\ncontrol PSC.