Bilayer photoanode approach for efficient In₂O₃ based planar heterojunction perovskite solar cells

Indium oxide (IO) has been demonstrated as an efficient and stable electron transporting layer for planar heterojunction perovskite solar cells, but dispersive pinholes in the sol-gel derived IO film limit its hole blocking capacity and corresponding device performance. In this study, we introduce an ultrathin TiO_x interlayer between Indium Tin Oxide (ITO) substrate and IO film via a low temperature TiCl₄ treatment method. By optimizing the process time, we obtain the optimal perovskite solar cells with a 30 min TiCl₄ treatment process, showing an impressive power conversion efficiency of 16.38%. In addition, the average device efficiency is improved from 13.7% to 15.1%, which is mainly attributed to the greatly improved fill factor. By means of investigating film roughness, pinhole effect and open circuit voltage decay, we find that the low-temperature processed TiO_x interlayer efficiently enhance the hole blocking capacity of the electron transporting layer, and consequently boost the device performance.