Molecular engineering of the organometallic perovskites/HTMs in the PSCs: Photovoltaic behavior and energy conversion

Abstract

In this work, a quantum chemistry study was performed on the organometallic perovskites/organic hole transfer materials (HTMs) in the perovskite solar cells (PSCs) from the molecular engineering viewpoint. Density functional theory (DFT)/time-dependent DFT (TD-DFT) was applied to investigate the electronic structures/excited state properties of a series of the perovskites, ABX3 (A=CH3NH3, NH4, CH(NH2)2, B˭Ge, Sn, Pb, X=Cl, Br, I). On the basis of the energy level of the perovskites, HTMs and TiO2, all perovskite compounds demonstrate a positive response to the hole/electron injection in the PSCs. A high occupied molecular orbital (HOMO) density of the HTMs, TPB, NPB, TPD, MDA1, MDA2, MDA3, TH101 and V950, are distributed over the whole molecule, homogeneously, which makes the hole transfer more proper. Investigation of the photovoltaic properties of the PSCs shows that they are strongly influenced by the chloride anion. The theoretical trend of the exciton binding energy is according to: F- < NH4- < MA-based perovskites. Considering different analyses show that the rate of the electron injection rate constant and the light harvesting efficiency increase by an increase in the electron driving force and electronic chemical potential. The correlation of the band gaps and the chemical nature of the substitutions in the perovskites shows a collapse by an increase in the cation size. Finally, it is proposed that ASnCl3 and AGeCl3 perovskites are better candidates to be applied in the PSCs as photosensitizers due to an improved incident photon to current efficiency.