CH3NH3PbI3-based hybrid organic-inorganic halide perovskite solar cells have currently attracted a lot of attention because its power conversion efficiency (PCE) is dramatically and continuously increasing. The solar cells have been extensively studied and developed based on several important challenges, i.e. (1) to improve quality of interface (surface) between perovskite and electron transport layer (e.g. TiO2 and ZnO), and between perovskite and hole transport layer (e.g. Spiro-OMeTAD and CuO) for enhanced carrier transport; (2) to reduce or stop using lead (Pb), which is toxic; and (3) to improve phase stability of perovskite increasing lifetime of devices, especially under humidity condition.
For the improvement of the interface (surface) quality, previous literature suggests that rough surfaces of CH3NH3PbI3 perovskite have higher possibility to be formedcomparedwiththe smooth one. Since the formation of vacancies on perovskite surfaces can stabilize its structure. Rough surface is usually coincident with interface defects and vacancies and able to introduce carrier’s traps and lowering carrier transport. Therefore, in this research project, we will firstly look for dopants which can stabilize the smooth surface by increasing of binding energy between atoms on surface. We will focus on the improvement of surface stability by Cl and Br doping on CH3NH3PbI3 surface. However, it was reported that the incorporation of Cl and Br into CH3NH3PbI3 perovskite leads to band gap broadening. Thus, we will also introduce Sn doping to tune for the proper value of band gap. The use of lead is then also reduced.
For the phase stability of perovskite, it is interesting that using Cs(Sn,Pb)I3-based instead of CH3NH3PbI3-based perovskite can overcome this problem due to the higher chemical stability of modified Cs(Sn,Pb)I3 compared with that of CH3NH3PbI3 perovskite. For instance, previous literature reported that CsSnI3+ 10% SnCl2 exhibit a stability ∼10 times greater than devices with the same architecture using CH3NH3PbI3 perovskite. In addition, CsPb1–xBixI3 compounds with (4 mol % Bi3+) demonstrate a high PCE of 13.21 % and maintain 68 % of the initial PCE for 168 hours under ambient conditions. Therefore, it is important to study both Cs(Sn,Pb)I3-based and CH3NH3PbI3-based perovskites for further development of perovskite-based solar cell. In this research project, all investigations will be performed under the framework of density functional theory which is a quantum-based theory extensively used for the investigation of materials properties.
Principal Investigator: Dr. Atchara Punya Jaroenjittichai