Study On Flexible Solar Cell And Photostability Based On Semitransparent Metal Electrode

Flexible Organic Solar Cells（FOSCs）have the advantages of light weight,good flexibility,and roll-to-roll production,and are widely used in aerospace,wearable devices,and photovoltaic building integration.The fabrication of FOSCs with good mechanical durability requires high-quality flexible transparent electrodes.Conventional ITO electrodes are not only expensive,but also have poor flexibility.In this thesis,PEI/Ag/PEI-Zn flexible electrodes were developed to improve the transmittance of Ag thin-film electrodes,and the FOSCs based on this electrode have excellent mechanical performance.To improve the transmittance of Ag thin film electrode,PEI/Ag/PEI-Zn electrode was prepared by introducing PEI as a seed layer to reduce the permeation threshold for Ag thin film growth and using PEI-Zn as a modification layer.The thickness of PEI-Zn was simulated and the optimal thickness of PEI-Zn layer was determined to be 40 nm.Finally,The transmittance of PEI/Ag/PEI-Zn electrode is 72.4%,which is 2.28 times that of Ag thin film electrode at wavelength of 650 nm and the square resistance was only 10.9Ω/sq.The FOSCs were then fabricated on PEN substrates with this electrode,and the cells were still able to achieve more than 60%of the initial Power Conversion Efficiency（PCE）after 500 consecutive bends,while the devices with PEN/ITO electrodes had only28%of the original PCE after 100 bends.Devices fabricated on PET and PDMS substrates demonstrate the universal applicability of this electrode on a variety of substrates.In addition,the effect of PEI-Zn annealing temperature on device performance was investigated for flexible substrates that are not resistant to high temperatures.The results show that at lower annealing temperatures,the J-V curve is more likely to have an obvious"S"shape and the Fill Factor（FF）is lower,and the FF gradually increases with increasing temperature.The device impedance and PEI-Zn conductivity tests show that the change of PEI-Zn properties by annealing temperature is mainly at the interface,and the morphological differences of PEI-Zn at different annealing temperatures indicate that Zn（OH）₂ may remain on the surface of PEI-Zn annealed at low temperatures,which affects the charge transport and leads to very low FF and PCE of the device.To reduce the damage of the active layer by UV light,a Distributed Bragg Reflector（DBR）was introduced in front of the Ag thin film electrode to reflect UV light.The simulation results show that the absorbance of the active layer near the wavelength of 380nm can be reduced from 0.57 to 0.21 by using the DBR structure,which verifies the theoretical feasibility of the scheme to apply the DBR structure in organic solar cells to reduce the UV incidence.The DBR with the structure of Mo O₃/Li F/Mo O₃/Li F/Mo O₃ was then vaporized on the PET substrate,and the PET/DBR demonstrated good reflectance in the UV band,and the EQE of the device with DBR was reduced from 35.4%to 5.4%at350 nm compared with the control group.The stability tests under sunlight and UV light showed that the FF and PCE of the devices with DBR structure decreased more slowly compared to the control devices,and the prepared DBR structure had a significant effect on improving the photostability of OSCs.