Effect of TiO₂ particle size and layer thickness on mesoscopic perovskite solar cells

Mesoporous TiO₂ (mp-TiO₂) layers are commonly used as electron transport layers in perovskite solar cells, which help to extract electrons from the perovskite light-absorbing layer and transport them to the electrodes. We investigated the effects of the layer thickness of mp-TiO₂ and particle size of TiO₂ on photovoltaic properties, in terms of the surface area of the mp-layer and the interfacial areas of the TiO₂ nanoparticles in the mp-layer. Various mp-TiO₂ layers with thicknesses of 150, 250, and 400 nm and particle sizes of 25 nm and 41 nm were prepared to compare the photovoltaic properties of such layer-containing perovskite solar cells. Time-resolved photoluminescence decay and impedance studies showed that interfacial resistance as well as perovskite-to-TiO₂ charge injection are important factors affecting photovoltaic performance. The deterioration of the photovoltaic parameters with increasing TiO₂/TiO₂ interfacial area also confirms that the interfacial series resistance that arises from these connections should be reduced to enhance the performance of mesoscopic perovskite solar cells.