Organic Ultra-thin Layer Modification Of CuSCN/Ag Interface In Perovskite Solar Cells

Organic-inorganic hybrid perovskite materials are gradually applied to solar cells due to their excellent photovoltaic properties including high absorption coefficient,high carrier mobility,long carrier diffusion length,tunable band gap and low-cost manufacturing technology.With the development from materials to structures and fabrication processes of devices,the power conversion efficiency(PCE)of perovskite solar cells(PSCs)has increased from 3.8%to recent 24.2%.As a result,PSCs have become an exploding area of research and been regarded as one of the most promising photovoltaic devices.Hole-transporting performance greatly affects the properties of the whole PSCs devices,so a lot of works have been done to find suitable hole-transporting materials.CuSCN has many irreplaceable advantages,such as well-matched energy level with perovskite materials,high hole-transporting mobility,low cost and flexible preparation processes,making it the most promising hole-transporting material in PSCs.However,there is potential induced degradation of the contact between metal electrode and CuSCN,which leads to poor operational stability in CuSCN-based PSCs.Therefore,it is significant to develop and refine some strategies to prevent the interfacial degradation in PSCs.In this paper,methylamine iodine lead(CH3NH3PbI3)is used as the active layer of perovskite solar cells,and CuSCN is used as the hole-transporting layer.An ultra-thin spacer layer is introduced to modify the CuSCN/Ag interface,as a result,the PCE and stability of devices were effectively improved.In the first pafrt,CuSCN film is prepared with solution spin-coating method,and the optimal preparation condition of CuSCN hole-transporting layer is explored.The results show that the PSC exhibits better photovoltaic performance when the CuSCN film is annealed at 60℃.Furthermore,when CuSCN concentration is 50 mg/mL and the device is spin-coated at 2000 rpm,the PCE of PSCs can achieve 5.95%.In the second part,based on the device structure and fabrication process of the first part,poly-TPD is used to modify the CuSCN/Ag interface of PSCs.When the concentration of poly-TPD solution is 2.5 mg/mL,the spin-coating speed is 2000 rpm and the annealing temperature of the film is 80℃,the PCE of the devices can reach 10.36%,which is 1.7 times of the pristine device.What’s more,the PCE can still maintain about 70%of the initial efficiency after 20 days in the air.The analysis of UV-vis spectrum,electrochemical CV curves and PL spectrum demonstrate that the introduction of poly-TPD can effectively enhance the hole-transporting ability.AFM shows that poly-TPD spacer layer can passivate the surface defects of CuSCN layer.The contact angle test shows the modified devices have an improved moisture resistance.In the third part,based on the device structure and fabrication process of the first part,the branched structured molecules CRA-mCP and CRA-TPA are respectively applied to modify the CuSCN/Ag interface.When the solution concentration is 4 mg/mL,the spin-coating speed is 3000 rpm,and the annealing temperature is 70℃,the PCE of the devices can achieve 8.69%and 11.97%respectively,increasing to 1.5 times and 2.0 times of the original efficiency.After 20 days in the air,the PCE of the devices can still maintain about 76%and 80%of the initial efficiency.The analysis of UV-vis spectrum,electrochemical cyclic voltammetry curves and PL spectrum show that CRA-TPA-based devices have better hole-transporting ability in comparison with CRA-mCP-based devices.AFM tells that both CRA-mCP and CRA-TPA can passivate the surface defects of CuSCN layer.The contact angle test illustrates that the modified devices have better moisture resistance than the original device.The results of CuSCN/Ag interface modified by three organic molecules show that triphenylamine-based poly-TPD and CRA-TPA have better hole-transporting property than carbazole-based CRA-mCP.Therefore,the devices modified by poly-TPD and CRA-TPA bear higher PCE.In addition,the excellent film-forming property of CRA-TPA,endowed by its branched structure,facilitates the interface contact in PSCs,thus improving the photovoltaic performance.