| Solar energy has enormous promise as an inexhaustible new energy source.Organic solar cells(OSCs)are a hot spot in the field of solar energy research because of the abundance of materials,simple process,environmental friendliness and ability to manufacture flexible devices.The Power Conversion Efficiency(PCE)for OSCs has recently been found to be higher than 19%.This article examines the modification of the cathode interface using the PBDB-T: IT-M system.Green,affordable,and ecologically friendly small molecule cathode interface materials are investigated through the use of quantum chemical calculations in order to enhance the PCE of devices.To start with,seven inexpensive small molecule cathode interface materials were quantitatively calculated: trans-cinnamic acid(TCA),P-coumaric acid,m-coumaric acid and trans-2-hydroxy-cinnamic acid,4-methoxy-cinnamic acid,2-methoxycinnamic acid and 3,4-dimethoxy-cinnamic acid.Density functional theory calculation is carried out through the quantum chemistry software Gaussian.The results of structural optimization,electrostatic potential diagram,Highest Occupied Molecular Orbital(HOMO)and Lowest Unoccupied Molecular Orbital were obtained,respectively(LUMO).The results of structural optimization indicate that TCA has a good planar structure.The electrostatic potential diagram shows a relatively balanced electrostatic potential distribution.And TCA has the matching LUMO energy level with the receptor material of organic photoactive layer.The potential of TCA as cathode interface material is predicted.Combined with the calculation results,the experiment was carried out.TCA was selected to replace the common cathode interface material PFN-Br,and the system with the active layer of PBDB-T: IT-M was modified.The device structure was ITO/PEDOT: PSS/PBDB-T: IT-M/TCA/Al.With the help of the cathode interface layer,the positive device was able to reach a PCE of 9.23%,which is43% higher than the device of without the cathode interface layer.Low-cost cathode interface material selection is completed,and the accuracy of calculation results is demonstrated through theoretical calculation and experiment.The hybrid cathode interfacial layer(PFN-Br:TCA)was prepared by doping the TCA in the PFN-Br solution,which was applied to the OSCs with PBDB-T:IT-M as the active layer.TCA and PFN-Br have good miscibility and complementary LUMO levels.A device with a structure of ITO/PEDOT: PSS/PBDB-T: IT-M/PFN-Br: TCA/Al was prepared by using PFN-Br: TCA with different doping ratios as cathode interface materials.When the doping ratio is 0.8:0.8 mg/ml,the optimal PCE of 11.38% is obtained,which is 7.8% higher than the 10.55% PCE of pure PFN-Br devices.Arrangement of work function,good interfacial contact and improved electrical conductivity are the key factors to improve the photovoltaic performance. |
