Fabrication And Optimization Of ZnO-Based Perovskite Solar Cells

Perovskite solar cells(PSCs) based on organometal halide perovskite CH3NH3 Pb X3(X = I, Br or Cl) light absorbers show a great application prospect due to their superb power conversion efficiency(PCE) and low cost. Zn O is an alternative electron-transport material for PSCs because of its excellent electron transport properties, various preparation methods and diverse nanostructures.In this thesis, Zn O nanostructures prepared with different methods were used as the electron-transport layer and CH3NH3 Pb I3 was used as the light-absorbing material. The influences of preparation methods and conditions of Zn O nanostructures and CH3NH3 Pb I3 films on the performance of PSCs were studied. The constraints on the performance of Zn O-based PSCs were analyzed, and the directions and strategies of optimization were suggested. The main contents are as follows:1. Effects of preparation methods and conditions of Zn O nanostructures on the performance of the PSCsThree kinds of Zn O nanostructures, namely sol-gel Zn O, sputtered Zn O and Zn O NR, prepared by the sol-gel method, magnetron sputtering and low-temperature hydrothermal synthesis were used as the electron-transport layer. The results showed that the thickness and annealing temperature of sol-gel Zn O film, the sputtering atmosphere for growing sputtered Zn O, and the length of Zn O NR have great influences on the performance of PSCs. PSC fabricated with sol-gel Zn O film prepared by spinning 4 times and annealed at 400°C showed the best performance, and sol-gel Zn O films prepared under that condition were used as the electron- transport layer for further studies.2. Effects of preparation conditions of CH3NH3 Pb I3 film on the performance of the PSCsCH3NH3Pb I3 films were prepared by the spin-coating-dipping method. The influence of Pb I2 solution spin speed, annealing temperature of CH3NH3 Pb I3 film, CH3NH3 I concentration and dipping time on the quality of CH3NH3 Pb I3 film and the performance of PSCs were studied. The results showed that, dense CH3NH3 Pb I3 films with uniform grain size can be obtained with moderate spin speed of Pb I2 solution; increasing the annealing temperature of CH3NH3 Pb I3 films is beneficial to improve the crystalline quality of CH3NH3 Pb I3, but too high the annealing temperature will lead to the decomposition of CH3NH3 Pb I3; large crystals grown from low CH3NH3 I concentrations showed higher short circuit current density(Jsc) due to a stronger light scattering and a better charge-extraction ability; prolonged dipping time can improve the conversion of Pb I2, and then the light absorbance of the film, but too long the dipping time is harmful to the performance of PSCs. PSCs fabricated under the condition of 3500 rpm for Pb I2 solution spin-coating, annealing temperature of 100°C, CH3NH3 I concentration of 0.038 M, and the dipping time of 40 s showed the best performance with Jsc of 21.2 m A·cm-2 and PCE of 6.06%.3. Performance analysis and optimization directions of Zn O-based PSCsCompared with the high-efficient PSCs, the lower PCE of Zn O-based PSCs prepared in this thesis can be ascribed to the low open circuit voltage(Voc) and the low fill factor(FF). Equivalent circuit analysis showed that the thicker Zn O electron transport layer with too many defects, bulk recombination in the perovskite light-absorbing layer, and pinhole in the films lead to a high reverse saturation current density, a high quality factor, a high series resistance, and a low shunt resistance. More compact Zn O and perovskite films with better crystallinity and fewer defects are essential to higher performance of PSCs.