Design,Synthesis And Device Performance Of High Efficiency Organic Photovoltaic Acceptor Materials

Polymer solar cells(PSCs)has attracted increasing attention in recent years,fueled by their unique advantages of low cost,easy fabrication,light weight,and the ability to fabricate flexible and semi-transparent devices.The development of new and high-efficiency organic photovoltaic materials is a critical step in single cell-based studies and the organic solar cells(OSCs)is an emerging focus of investigation.The primary objective was to modifies the conjugated main chain and side chain of the acceptor material to control the absorption range,molecular energy level and micro-morphology of the blended film and other characteristics of the active layer,and obtain a series of high-performance PSCs.The results of the study were as follows:(1)To examine the effects of these different fluorination position on the photovoltaic performance of A-D-A type small molecule acceptor(SMA)materials.Herein,we introduced the fluorine atoms into the conjugated main chain and the electron-deficient end-group(EG)of the ITIC and synthesized three kinds of A-D-A SMA materials(2FITIC-0F,2FITIC-2F and 2FITIC-4F)can be obtained.With the introduction of different numbers of F atoms into different position of ITIC,the energy level and absorption of corresponding SMAs change obviously.Compared with ITIC,the SMA materials decorated with F atoms exhibit lowered LUMO and HOMO levels.In addition,the LUMO levels of corresponding SMAs could be gradually downshifted by increasing the number of F atoms.Therefore,the open-circuit voltage(Voc)of the corresponding PSCs devices gradually decreases from 1.01 V to 0.83 V.Among theses PSCs devices,the PSCs devices based on PM6:2FITIC-2F blend deliver the highest PCE of 11.3%.This study’s findings suggest that the fine regulation of small molecule acceptor materials can improve photovoltaic performance by promoting efficient active layer materials charge transfer.(2)In order to improve the device performance of A-DA’D-A type small molecule acceptors.Herein,we design and synthesize a novel SMA named Y6-Si via incorporating a siloxane-terminated side chain into the N-position of Y6 core.Compared with the classical Y6,Y6-Si exhibits a better solubility,an up-shifted LUMO energy level,a more ordered molecular packing,and a higher electron-mobility.As a result,the PM6:Y6-Si-based PSCs achieved a much better PCE of 16.6%with a higher Voc of 0.90 V,a higher short-circuit current density(Jsc)of 24.0 mA cm-2 and a higher fill factor(FF)of 0.77 than those of PSCs based on PM6:Y6(PCE=13.0%,Voc=0.81 V,and FF=0.69).It is concluded that in many respects incorporation of siloxane-terminated side chain into Y6 core is an ideal model for improve device performance of SMAs.(3)To realize the high-efficiency and green solvent processed PSCs devices,we design and synthesize a low bandgap acceptor Y6-Si-4C1 by replacing the fluorine atoms of Y6 with chlorine atoms and introducing siloxane-terminated side chain into Y6 core.Y6-Si-4Cl exhibits a better solubility in non-halogen solvent toluene compared with the classical Y6.The PSCs devices based on PM6:Y6-Si-4C1 blend achieve an outstanding PCE of 15.9%,which is higher than that of PM6:Y6 device 10%(14.4%)with the halogen-free toluene as the green processing solvent,1 vol%1-methylnaphthalene(MN)as the solvent additive and thermal annealing(TA).Key findings demonstrate that regulating the dissolution behavior of SMAs via molecular design is a feasible way to fabricate efficient non-halogen solvent processed PSCs devices.(4)We design and synthesize a novel narrow-bandgap polymer acceptor PG1 with a polymerized A-DA’D-A type small molecule acceptor as a acceptor unit and thienyl substituted benzo[1,2-b:4,5-b’]dithiophene as a donor unit,which shows a broad and strong absorption in the region of 550～900 nm with a narrow optical bandgap(Egopt)of 1.42 eV,a high maximum extinction coefficient of 1.19 ×105 cm-1 and a high electron mobility of 6.49×10-4 cm2 V-1 s-1,which is benefitted from narrow bandgap,strong absorption and high electron mobility of its original SMA building blocks.Furthermore,PG1 shows an expected up-shifted LUMO energy level of-3.81 eV compared to it SMA building block,which is beneficial for achieving a higher Voc in its all-PSCs.The optimal all-PSCs based on PBDB-T:PG1 blend achieved an outstanding PCE of 11.5%with a high Voc of 0.94 V,a Jsc of 17.8 mA cm-2,a FF of 0.69 and a low energy loss of 0.48 eV when processed with 1-chloronaphthalene(CN)as solvent additive.Here we report examples of fused A-DA’D-A type heptacyclic ring as electron acceptors that are effective way in efficient polymer acceptor materials.