Effect Of Interfacial Modified Layer Of ZnO Layers On The Performance Of Organic Solar Cells

Over the last decade,non-fullerene-based organic solar cells（NFA OSC）have received significant attention due to their ease of preparation,low cost,simplicity of process and ease of fabrication of flexible devices,and their power conversion efficiency（PCE）has increased from 11%to over 19%,marking a further step in their commercialization.However,compared to other photovoltaic technologies（silicon-based,perovskite-based）,the performance and stability of OSCs still need to be optimized to make them commercially competitive.In general,due to their structural characteristics,devices with inverse structure have better stability and similar device performance than conventional devices,but even so,poor contacts（photochemical degradation）between the electron transport layer（usually a metal oxide,ZnO has been chosen for this thesis）and the active layer,as well as defects on the surface of the ZnO film,limit further improvements in the performance and stability of OSCs.The ZnO film is selected for this thesis.Based on this,the defects of the ZnO surface are modified by adding a ZnO interfacial modified layer.1.To address the problems of reduced stability and limited performance caused by the presence of traps on the ZnO surface,this work selectively uses Y6,a small molecule material with the same acceptor as the active layer（PM6:Y6）,as the interface modified layer to optimize the trap state on the ZnO surface and improve the interfacial contact characteristics between the functional layers,thereby improving the performance and stability of organic solar cell devices.The results show that the Y6 interfacial modified layer can effectively improve the short-circuit current density(J_SC)and fill factor（FF）of the OSC device by the optimized process.Further,the relationship between J_SC and open-circuit voltage(V_OC)and incident light intensity(P_light)is analyzed and the Y6 interfacial modified layer was found to be effective in passivating interfacial defects,thereby improving device performance by reducing single molecules recombination and trap recombination within the device.2.In order to analyze the mechanism of the Y6 interfacial modified layer to enhance the device performance,two Y6 derivatives,BTP-e C9 and L8-BO,which have similar chemical structures to Y6,were selected as interfacial modified layers and the corresponding devices were prepared to investigate the effect of Y series small molecules on the device performance in order to improve the feasibility of the method.By optimizing the preparation conditions,the BTP-e C9 and L8-BO interfacial modified layers also improved the J_SC and FF of the OSC devices to different degrees,and the relationship of J_SC and V_OC with P_light are characterized and the results show that both the BTP-e C9 and L8-BO interfacial modified layers have an inhibitory effect on single-molecule complexation and trap complexation within the device（the same way as the Y6interfacial modified layers）,contribute to improving device performance.3.After determining the optimized process,more detailed tests are carried out using three Y-series small molecule receptor materials as interfacial modified layer to determine the reasons for the improved device performance.It is found that the interfacial modified layer optimizes the surface morphology of the films inside the device,thereby improving performance and stability.The experimental results show that the addition of the interfacial modified layer passivates the surface defects of ZnO,thereby improving the interlayer charge transfer capability of the devices,which improves the J_SC,FF and PCE of the OSCs,with the highest device PCE reaching 16.02%in the PM6:Y6 active layer material system.Due to the protection of the interfacial modified layer,the OSCs exhibit outstanding stability compared to standard devices（without interfacial modified layer）,maintaining 80%of the performance of the devices for 150 hours.In summary,the ZnO interfacial modified layer prepared in this thesis can simultaneously improve the power conversion efficiency and stability of OSCs,effectively passivate the surface defects of the ZnO film,reduce the chance of carrier recombination during the internal carrier transport of the device,increase the dissociation efficiency of the excitons in the device,providing a simple and effective idea for future research in the field of interfacial modified of OSCs.