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

The influence of TiO2 layer on the ultimate efficiencies, eta, i.e. efficiencies without considering carrier recombination, for the planar and nano-textured CH3NH3PbI3 (MAPbI(3)) perovskite solar cells (SCs) are investigated. In planar TiO2/MAPbI(3) heterojunction SCs, in order to achieve the largest power conversion efficiency (PCE), the TiO2 layer thickness, d(1), is important. With the finite difference time domain (FDTD) method, we demonstrated that when the MAPbI(3) layer thickness, d(2), is 250 nm, which is a common-most MAPbI(3) layer thickness for perovskite SCs, eta achieves maximum when d(1) is 80 nm. Fabricating nano textures on SC surface is an important method to improve the PCE. We studied the effects of d(1) and d(2) on the optimized eta, eta(0), for two kinds of nano-textured perovskite SCs: the SCs with the nontextured TiO2 layer and the column-shaped nano hollow (CLH) textured MAPbI(3) layer, defined as the nontextured-TiO2/CLH-MAPbI(3) SCs, and the SCs with CLH textured TiO2 and CLH textured MAPbI(3) layers of the same hollow axes and radius, defined as the CLH-(TiO2/MAPbI(3)) SCs. Generally, when d(1) and d(2) are fixed, eta(0) for the CLH-(TiO2/MAPbI(3)) SC is larger than that for the nontextured-TiO2/CLH-MAPbI(3) SC by ca. 5%.