The Simple Strategies For Improving Performance Of Non-Fullerene Polymer Solar Cells

Organic solar cells(OSCs)have attracted much attention resulting from their particular advantages of low-cost,lightweight,and flexibility.Organic solar cells based on non-fullerene-based systems have made significant improvements in efficiency,with certified power conversion efficiencies(PCEs)rapidly improving from 11% to extend 18% over the past five years.For the large-scale commercialization of organic solar cells in the future,it is necessary to further improve the efficiency and stability of the devices.Therefore,this paper selects polymer: narrow band gap non-fullerene small molecule photovoltaic system as the research object,focusing on the selection and control of the third component in solar cells,the influence and removal of trace water in materials and solvents,the selection and judgment of polymer donor molecular characteristics,to research the influence of several strategies on device performance.It is mainly divided into the following three parts:(1)Study on the efficiency and stability of high-performance organic solar cells based on the polymerization extent of polymersIn this work,a series of PM6 polymers with different weight-average molecular weights(Mws)and polydispersity index(PDI)were synthesized.While the effects of the degree of PM6 polymerization on the efficiency and degradation behaviors of the photovoltaic systems based on Y6 as acceptor are investigated systematically.Studies have shown that with the increment of polymer Mw,the efficiencies of high-Mw PSCs are higher than those of small-Mw devices,and with the increment of polymer PDI,the PCEs decreased gradually.PM6 polymers with high-Mw values,which possess high PCEs of more than 16%,showed the low photobleaching rates in blends as well as high storage and mechanical stabilities in devices.In contrast,the variations of the stabilities mentioned above are not apparent in the PM6-PDI based photovoltaic systems.In addition,our results demonstrated that PM6 with a moderate Mw exhibits higher photostability in devices and thermal stability in BHJ blends.Further analysis showed that the substantial differences in illumination and thermal stabilities among these systems mainly derive from the molecular interactions,and degree of trap density under external stress factors.(2)Improve the efficiency and stability of organic solar cell devices by removing water-induced trapsIn this work,we demonstrated a solvent-water evaporation(SWE)strategy,which can effectively remove the water-induced traps that are omnipresent in photoactive layers,leading to a significant improvement in device performance.A higher power conversion efficiency(PCE)of 17.10% and a better device photostability are achieved by using this SWE method,as compared to the un-treated binary PM6:Y6 system(15.83%).In addition,we revealed the unique advantages of this strategy,including good charge transport and extraction properties,and good universality in OSCs.What is more,organic light-emitting diodes and organic field-effect transistors are also investigated to demonstrate the applicability of this SWE approach.(3)The effect of similar materials as the third component on device efficiency and stabilityIn this work we introduced and constructed two different ternary solar cells based on J101:Me IC host films separately blended with two distinct near-IR non-fullerene acceptors,F-IXIC and Cl-IXIC.Both of the three components effectively improve the light stability and thermal stability of the device.Notably,the J101:Me IC host devices with a PCE of 11.83% were improved to 14.08% by loading 40 wt% F-IXIC,but reduced to 9.32% by loading Cl-IXIC with the same content.the working mechanism and morphology characteristics of the two ternary systems were carefully analyzed by physical morphology test and surface energy calculation,and the reasons for the great difference between PCE and filling factors(70.19% for F-IXIC ternary system and 50.24% for Cl-IXIC ternary system)were discussed.The investigated results suggest that localization driving force of sensitizers explained in terms of surface energy can rationally control the efficiency-stability gap of ternary solar cells.