Liquid phase deposition of TiO₂ nanolayer affords CH₃NH₃Pbl₃/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/CH₃NH₃Pbl₃/nanocarbon, we have achieved a V_oc as high as 1.07 V, the highest value reported so far for hole transporter-free CH₃NH₃Pbl₃ 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 CH₃NH₃Pbl₃ 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 CH₃NH₃Pbl₃ 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.