Liquid phase deposition of TiO2 nanolayer affords CH3NH3PbI3/nanocarbon solar cells with high open-circuit voltage

Hybrid organic/inorganic perovskite solar cells are attracting intense attention and further developments largely hinge on understanding the fundamental issues involved in the cell operation. In this paper, a liquid phase deposition (LPD) method is developed to design and grow a TiO2 nanolayer at room temperature for carbon-based perovskite solar cells. The TiO2 nanolayer grown on FTO glass is compact but polycrystalline consisting of tiny anatase TiO2 nanocrystals intimately stacked together. By directly exploiting this TiO2 nanolayer in a solar cell of TiO2 nanolayer/CH3NH3PbI3/nanocarbon, we have achieved a V-oc as high as 1.07 V, the highest value reported so far for hole transporter-free CH3NH3PbI3 solar cells. This is rationalized by the slower electron injection and longer electron lifetime due to the TiO2 nanolayer, which enhances the electron accumulation in CH3NH3PbI3 and consequently the V-oc. By employing a rutile TiO2 nanorod (NR) array as a base structure for the LPD-TiO2 nanolayer to support the CH3NH3PbI3 layer, the photocurrent density is considerably increased without obviously compromising the V-oc (1.01 V). As a result, the power conversion efficiency is boosted from 3.67% to 8.61%. More elaborate engineering of the TiO2 nanolayer by LPD in conjunction with judicious interfacing with other components has the potential to achieve higher performances for this type of solar cell.