Studies On ZnO-based Planar Heterojunction Perovskite Solar Cells

In recent years, perovskite solar cells(PSCs) based on organic-inorganic metal halide perovskites such as CH3NH3 Pb I3 have attracted extensive research interesting worldwide, and achieved a power conversion efficiency(PCE) beyond 22%. In this thesis, planar heterojunction PSCs were fabricated based on Zn O electron transport layer(ETL), which has excellent electron transport property and is easy to prepare under low temperature. The effects of preparation methods of Zn O ETLs and CH3NH3 Pb I3 light absorption layers on the performance of PSCs were studied. A modified method to fabricating CH3NH3 Pb I3 layers was presented, and PSCs with improved performance were fabricated under low temperature(< 150°C). The main contents are as follows.1. Effects of preparation methods of Zn O ETLs on the performance of the PSCsn-Zn O ETLs were prepared by spinning Zn O nanoparticle suspensions and it was found that the thermal stability of CH3NH3 Pb I3 decreased on the n-Zn O layers. The influences of spinning times and post-treatment temperature on the performance of PSCs were studied, and the highest PCE > 7% was achieved for the devices fabricated under optimal conditions of 4 spinnings and 150°C post-treatment. The performance of PSCs with n-Zn O or sol-gel prepared Zn O(s-Zn O) as the ETLs were analyzed and it was found that open circuit voltage(Voc) and fill factor(FF) of n-Zn O based PSCs were greater because of its dense Zn O ETLs, while short circuit current density(Jsc) of s-Zn O based PSCs were higher for the better conversion of Pb I2 to CH3NH3 Pb I3 on s-Zn O ETLs.2. Effects of the treatment of Pb I2 films on the performance of the PSCsIt was impossible to increase the quality of CH3NH3 Pb I3 layers by annealing the layers at an elevated temperature or for a prolonged period, because of the limitation of thermal stability of CH3NH3 Pb I3 on n-Zn O layers, as mentioned above. Therefore, our study focused on the precursor Pb I2 film. As the performance was poor for PSCs fabricated with conventional thermal annealing(TA), two modified methods, namely solvent vapor annealing(VA) and vapor exposure(VE), were proposed for the treatment of Pb I2 films. PCEs of devices fabricated with VA and VE treatments under N, N-dimethyl formamide(DMF) vapor atmosphere increased from 2.28% with TA treatment to 6.68% with VA treatment and 6.78% with VE treatment, respectively. Under the optimal precursor concentration of 1.33 M and VA temperature of 70°C, the best devices fabricated with VA treatment showed PCEs of 8.52% and 10.31%, respectively. When VA treated with dimethylsulfoxide(DMSO) vapor, Pb I2 was converted to Pb I2(DMSO), facilitating the further fully conversion to CH3NH3 Pb I3, and CH3NH3 Pb I3 films with high quality were obtained. Thus, PCE of the best device improved to 11.72%.