Investigation Of Carbon Counter Electrode Perovskite Solar Cells Based On Cu₂MS₃（M=Sn,Ge） Hole Transport Layer

Organic-inorganic hybrid perovskite solar cells have attracted extensive attention from researchers due to their excellent light absorption coefficient,long-range carrier diffusion length and simple preparation process.Since the discovery of perovskite solar cells in 2009,the certified efficiency of perovskite solar cells in the laboratory has reached 25.73%,which is comparable to crystalline silicon solar cells that have been commercialized for many years.However,at present,perovskite solar cells have not been commercialized at a large scale.The main problem is that perovskite materials are very sensitive to water and oxygen and are easily destroyed and decomposed.Moreover,highly efficient perovskite solar cells rely on organic hole transport materials and expensive gold electrodes.The high cost also limits the commercialization of perovskite solar cells.Carbon counter electrode-based perovskite solar cells occupy a place in perovskite solar cells due to their excellent stability and low cost.However,the traditional carbon counter electrode-based perovskite solar cells are hole transport layer free and suffers from serious charge carrier recombination at the perovskite/carbon interfaces,which result in a large efficiency gap between the carbon counter electrode-based perovskite solar cells and the traditional metal electrode-based perovskite solar cell.In this thesis,we have introduced inorganic p-type semiconductors as hole transporting layers in the carbon counter electrode-based perovskite solar cells in order to improve the power conversion efficiencies.The specific work is as following:（1）We synthesized Cu₂Sn S₃ nanocrystals using hot injection method and evaluated their ability as hole transport layer in carbon counter electrode based-perovskite solar cells for the first time.Cu₂Sn S₃ nanocrystals were used as hole transport layer in perovskite solar cells with a structure of FTO/Sn O₂/Perovskite/Cu₂Sn S₃/Carbon.It was found that the Cu₂Sn S₃ nanocrystals hole transport layer can effectively extract photogenerated holes from the perovskite film and inhibit the recombination of carriers.The thickness of the hole transport layer was optimized by changing the spin coating speed.When the rotation speed was 4000 rpm,the device performance was the best,and the corresponding photoelectric conversion efficiency was 16.75%.At the same time,we tested its storage stability,and found that the performance of carbon counter electrode-based perovskite solar cells based on Cu₂Sn S₃ nanocrystals hole transport layer had almost no attenuation within 30 days,indicating that the perovskite solar cells with this structure had good storage stability.（2）We replace the Sn element in Cu₂Sn S₃ with the Sn-homologous Ge element,Cu₂Ge S₃ nanocrystals were successfully synthesized by one-pot method.The valence band energy level of Cu₂Ge S₃ is slightly higher than that of perovskite materials,and a suitable energy barrier can be formed at the conduction band,which helps to extract holes in perovskite and inhibit the recombination of carriers at the interface.When Cu₂Ge S₃ nanocrystals are used as the hole transport layer of carbon counter electrode-based perovskite solar cells,the highest efficiency can reach 19.0%,which is one of the highest efficiencies of similar solar cells reported so far,and it exhibits excellent long-term stability.Our results show that Cu₂Ge S₃ nanocrystals are a promising inorganic hole transport material that can be optimized to further improve the performance of carbon counter electrode-based perovskite solar cells.