FAPbI3 planar heterojunction perovskite solar cells with doped zinc oxide layer

Abstract

My MS research has focused on planar heterojunction perovskite solar cell as promising technology that might be renewable energy resources and the next generation flexible device. Hybrid organic-inorganic perovskite materials based on lead halides has attracted substantial attention due to their outstanding physical properties such as high absorption coefficients, excellent carrier transport with long electron-hole diffusion lengths, low exciton binding energies and easily tunable energy band gaps. These superb physical characteristics have led to high power conversion efficiencies (PCE) since the first research in solution processing perovskite solar cells (PeSCs) was reported in 2009. Perovskite solar cell has two types; n-i-p and p-i-n structures and researchers have focused on finding better method to produce uniform perovskite films with large crystal domains and complete surface coverage. And they have studied diverse approaches to improve device performance via control of the film morphology such as interface engineering, induced crystallization with non-solvents, incorporation of processing additives and so on. In the case of interfacial engineering, not only obtaining suitable interfacial condition for charge transport, but also tuning the energy band structure via doping process is still one of most widely employed techniques. In this regard, ZnO nanoparticles (NPs) have been used as an ETL in our work due to their outstanding electrical and optical properties as well as their easily controlling doping, morphology and composition compared to conventional TiO2 ETLs. Moreover, ZnO NPs films may be coated without any thermal treatment and while ZnO possesses a higher conductivity than TiO2, which may facilitate electron transport. Despite the advantages of ZnO compared to TiO2, ZnO layer has a problem with methylammonium lead iodide (MAPbI3, CH3NH3PbI3). Since ZnO has a natural base characteristic, it is able to deprotonate the methylammonium cation and hence degrade the MAPbI3 layer into methylamine and PbI2 at elevated temperature. During my research, I focused on n-i-p structures using ZnO NPs modified with various alkali metal carbonate including Li2CO3, Na2CO3, K2CO3 and Cs2CO3, which serve to tune the energy band structure of the ZnO ETL. Furthermore, I changed the MAPbI3 to FAPbI3 to get higher thermal stability.