Influence of TiO2 layer on ultimate efficiencies for planar and nano-textured CH3NH3PbI3 solar cells

Abstract

The influence of TiO2 layer on the ultimate efficiencies, η, i.e. efficiencies without considering carrier recombination, for the planar and nano-textured CH3NH3PbI3 (MAPbI3) perovskite solar cells (SCs) are investigated. In planar TiO2/MAPbI3 heterojunction SCs, in order to achieve the largest power conversion efficiency (PCE), the TiO2 layer thickness, d1, is important. With the finite difference time domain (FDTD) method, we demonstrated that when the MAPbI3 layer thickness, d2, is 250 nm, which is a common-most MAPbI3 layer thickness for perovskite SCs, η achieves maximum when d1 is 80 nm. Fabricating nano textures on SC surface is an important method to improve the PCE. We studied the effects of d1 and d2 on the optimized η, η0, for two kinds of nano-textured perovskite SCs: the SCs with the nontextured TiO2 layer and the column-shaped nano hollow (CLH) textured MAPbI3 layer, defined as the nontextured-TiO2/CLH-MAPbI3 SCs, and the SCs with CLH textured TiO2 and CLH textured MAPbI3 layers of the same hollow axes and radius, defined as the CLH-(TiO2/MAPbI3) SCs. Generally, when d1 and d2 are fixed, η0 for the CLH-(TiO2/MAPbI3) SC is larger than that for the nontextured-TiO2/CLH-MAPbI3 SC by ca. 5%.