Perovskite Film Crystal Growth And Interfacial Materials In Perovskite Solar Cells

Recently, perovskite solar cells ?PSCs? have attracted significant attention due to their flexibility, low cost, simple preparation process and high power conversion efficiency ?PCE? over 22.1%. The high photovoltaic performance relies to not only the performance and quality of perovskite film but also the nature of the contact layer. On the one hand, perovskites have been used as absorbers for the generation,transport and separation of charge carrier owing to their high carrier mobility, long diffusion length, large absorption coefficient and tunable optical band gap.Meanwhile, efforts have been made to decrease the charge recombination by improving the quality of perovskite film, thus enhancing the photovoltaic performance of PSCs. It has been one of the hot fields of the research. On the other hand, the contact layer adjacent to the perovskite one has to own excellent photoelectric properties with proper energy level in order to achieve the efficient charge extraction and transport. We mainly focus on the two aspects as following.For one thing, the high- quality perovskite film is achieved by improving the film preparation process. For another, the PCE of PSCs was further improved by exploring the key factors influencing the interfacial charge extraction. The specific research contents are as follows:The annealing temperature ?Ta? could influence the evaporation of the solvent and the nucleation and growth during preparation of the film. Thus, it is beneficial for the improvement of photovoltaic performance by exploring the Ta effect on the CH₃NH₃PbI₃ PSCs. By utilizing a two-step technique, the Ta dependences of optical absorption, grain size, as well as crystalline of CH₃NH₃PbI₃ thin film have been revealed. It is found that the grain size of CH₃NH₃PbI₃ film increases monotonically with Ta. Meanwhile, the decomposed PbI2 emerges when Ta exceeds 120 ? and its content increases rapidly as Ta increases further. Consequently, the optical absorption of the CH₃NH₃PbI₃ film and the efficiency of PCSs get a maximum at Ta= 120 0C simultaneously. The highest and average device performance of PCSs is achieved to be 17.61% and 16.40%, respectively, via this method. These results confirmed the key role played by temperature and provided a route to the performance-optimization of PSCs.The performance of planar PSCs is quite dependent on the interfacial conditions and then the interfacial band engineering is very important not only for the effective improvement of PCE but also for the better understanding of the charge transfer in the cells. In this report, the band engineering of the ZnO based electron transport layer ?ETL? in PSCs was studied by modulating Sn-doping level ?0 ? x ? 0.2?. A V-like variation of work function ?Wf? as function of Sn-doping level in Zn1-x,SnxO films was realized from 4.23 to 4.39 eV. As a result, the photovoltaic performance of PSCs with the Zn1-xSnxO ETLs was adjusted and the V-like tendencies of photovoltaic parameters of devices, such as open-circuit voltage ?VOC? and the short-circuit current ?Jsc?, were found. The maximum values of VOC and Jsc were achieved as 1.04 V and 24.13 mA cm^-2 with an ETL of Zn0.8Sn0.2O, respectively,which corresponds to a highest PCE of 16.47% for ZnO-based pervoskite solar cells with a large fill factor of 65.62.