Research On High Efficiency Ternary Thick Film Organic Solar Cells

Organic solar cells(OSCs)have become one of the most popular third-generation photovoltaics in recent years because of their flexibility,lightweight,solution processability,etc.Due to the optimization of the device structure,abundant interfacial modifications,the diversification of post-processing,and the rapid development of materials,the single junction Power conversion efficiency(PCE)of OSCs has exceeded 18%.However,most reported high-efficiency OSCs are very sensitive to the thickness of the active layer.How to reduce the significant reduction of PCE as the active layer thickness increases is a critical issue to be solved in the large-scale production of OSCs.Ternary strategy is an effective method to improve device performance,which has many advantages such as enhancing light capture and optimized active layer morphology.In this paper,we focus on improving the PCE of thick film OSCs by ternary strategy and investigating the intrinsic mechanism of the third component in reducing the PCE loss of thick-film active layer devices.Hope to provide a reference for the preparation of OSCs devices with larger thickness processing windows.Firstly,a series of devices with different active layer thicknesses have been prepared by introducing a nematic liquid crystalline small molecule donor BTR-Cl into the PM6:Y6 host system.The PCE of the ternary device maintained 15.28% compared to 12.94% of binary devices with an active layer thickness of 300 nm.By comparing the UV-Vis absorption of the etched blends,the vertical distribution of the characteristic elements in Depth X-ray Photoelectron Spectroscopy(DXPS),the crystallization behavior of different active layers from Grazing incidence wide angle X-ray scattering(GIWAXS),and the nanoscale morphology from atomic force microscopy(AFM)and transmission electron microscopy(TEM)tests,etc.,we attribute the improvement of the performance of the ternary devices to the optimized crystallization behavior and more suitable vertical phase distribution driven by differences in miscibility between components.After the addition of the third component,the active layer ensures sufficient phase separation with improved charge transport,it promotes the balance of charge transport and reduces non-radiative recombination.This work shows that the introduction of highly crystalline donor molecules as the third component in the active layer has great potential to achieve high efficiency organic thick film devices.Then,we choose the blade coating method to deposit the active layer because blade coating is more compatible with the roll-to-roll process for large-area processing.We chose toluene as the solvent for the active layer for it is more environmentally friendly.We added the strong crystalline small molecule DRTB-T-C4 to PM6:BTPBO-4Cl and obtained 17.09% PCE for thin film devices with active layer thickness of150 nm and 15.66% PCE when the thickness was increased to 350 nm.We found that the third component was compatible with the main components and distributed at the donor/acceptor interface,which promoted the excitons separation and charge transfer.And the addition of DRTB-T-C4 shortens the drying time of the thick film active layer,alleviates the aggregation of the thick film active layer during the drying of the high concentration solution,and makes the active layer more uniform and homogeneous.The optimized morphology of the ternary active layer leads to higher mobility of carriers,higher charge collection efficiency,and reduced recombination.As a result,the ternary devices maintained a high PCE even when the active layer thickness increased.This work illustrates that the introduction of strong crystalline donor small molecules as the third component in the active layer effectively reduces the sensitivity of the active layer to the thickness and provides more references for compatible future large-area printing processes.