Effect of compact TiO₂ layer on structural, optical, and performance characteristics of mesoporous perovskite solar cells

We investigated the effect of a compact TiO₂ (c-TiO₂) layer on the structural, optical, and performance characteristics of mesoporous perovskite solar cells (mp-PSCs) with fluorine-doped tin oxide (FTO)/mesoporous TiO₂ with or without c-TiO₂ layer/perovskite/spiro-OMeTAD/Au structure. The mp-PSCs with the c-TiO₂ layer exhibited a dense and pinhole-free perovskite film with a highly crystalline structure. On the other hand, the mp-PSCs without the c-TiO₂ layer suffered from severe recombination problems at the perovskite/FTO interface, which was examined by impedance spectroscopy analysis. However, the c-TiO₂ layer of the mp-PSCs played a significant role in reducing the recombination of carriers, due to the high carrier recombination resistance at the perovskite/FTO interface. As a result, the mp-PSCs with the c-TiO₂ layer showed a high conversion efficiency of 15.51%, together with an open-circuit voltage of 1.04 V, a short-circuit current density of 20.44 mA/cm² and a fill factor of 72.73%. In addition, the c-TiO₂ layer minimized the hysteresis in the current density-voltage (J-V) curves measured for the mesoporous perovskite solar cells.