Radio Frequency Magnetron Sputtering Deposition Of TiO₂ Thin Films And Their Perovskite Solar Cell Applications

Organic inorganic hybrid perovskite materials CH3NH3 Pb X3(X=Cl, Br and I)won the widespread attention due to its high optical absorption coefficient, low cost and easy preparation advantages. Perovskite solar cells(PSCs) based on CH3NH3 Pb X3 brought a ray of hope for future energy crisis and its power conversion efficiency increased from 3.8% in 2009 to 22.1% in 2016. The diversity of preparing methods for CH3NH3 Pb X3 make it more attractive, including one step solution method, two step continuous deposition method, vapor deposition and vapor-assisted solution process method. Meanwhile, the preparation process of electron transport material(ETM, Ti O2, Zn O) was also widely studied, spin-coating precursor, spray pyrolysis, atomic layer deposition method are included. By analyzing the work principle and summarizing the existing problems in the preparation of the thin film, we first report the radio frequency magnetron sputtering method for Ti O2 electron transport layer and thermal evaporation combined with immersion(evaporation & immersion) process for CH3NH3 Pb I3 in planar heterojunction PSCs. Typical solution-based synthesis of cp-layer for PSCs involves low-quality of thin films, high-temperature annealing, non-flexible devices, limitation of large-scale production. In this research, using radio frequency magnetron sputtering(RFMS), the thickness of cp-Ti O2 layers could be controlled by deposition time; CH3NH3 Pb I3 films were prepared by evaporation & immersion(E & I) method, in which Pb I2 films made by thermal evaporation technique were immersed in CH3NH3 I solution. The devices exhibit power conversion efficiency(PCE) of 12.1% and the photovoltaic performance can maintain 77% of its initial PCE after 1440 h. The method developed in this study has the capability of fabricating large active area devices(40×40 mm2) showing a promising PCE of 4.8%. Low temperature and flexible devices were realized and a PCE of 8.9% was obtained on the PET/ITO substrates. The disadvantages of traditional methods such as high temperature annealing, solvent consumption, and no large area preparation are solved. In the modulation mechanism, we analyzed the carrier transport effects of electron transport layer, CH3NH3 Pb X3 crystallization on the device performance and the existed hysteresis phenomenon in the PSCs. Compared with the conventional spin coating method, RF magnetron sputtering assisted E&I method shows more simple, easily controlled process for PSCs. The lower cost of equipment and material are suitable for future commercialization process and large-scale industrialization demand. At the same time, it has laid a solid foundation for the preparation of high efficiency and stable perovskite solar cell devices.