A Research Of High Efficiency Ternary Non-fullerene Organic Solar Cells

Organic Solar Cells?OSCs?are considered to be a new generation of green energy technologies with significant industry prospects,which have the advantages of low cost,light weight,flexibility,simple preparation process and easy in large-scale manufacture.In recent years,nonfullerene-based OSCs have attracted considerable attention due to their brilliant characteristics of simple synthesis pathway and comfortably tunable molecular energy levels.However,there are some unavoidable defects in the main non-fullerene materials used currently,such as difficulty in regulation of film morphology and low charge mobility.Ternary strategy has been proven to be an effective way to broaden the absorption spectrum of active layer,enhance short circuit current density(J_SC)and fill factor?FF?of devices.But low power conversion efficiency?PCE?and poor stability are currently the main problems in the research of ternary OSCs.To address the above issues,we adopted a ternary strategy to optimize the performance of the device in this paper,which was based on the classical non-fullerene system PTB7-Th:ITIC.High efficiency ternary nonfullerene OSCs with high stability were obtained.The main work and conclusions of this paper are summarized as follows:1.A phenanthroimidazole-based small molecule material named TPPI-TPE was doped into the PTB7-Th:ITIC system to achieve high effiency ternary nonfullerene OSCs.The ternary OSCs with doping ratio of 10 wt%achieved an efficiency up to 9.50%,which represented a²0%enhancement in comparison with the control binary device?7.88%?.FF of the ternary devices increased from 57.88%to 65.63%.The results of research show that TPPI-TPE has complementary absorption position with the binary main system.The introduction of TPPI-TPE can enhance the light absorption of the blend films.More importantly,the morphology of the active layers was optimized by promoting the crystallization of polymer donors and enhancing the intensity of their?-?stacking.Exciton dissociation and charge transfer in the blend films were improved simultaneously.2.On this foundation,a fluorescent dye molecule Coumarin7?C7?was doped into the PTB7-Th:ITIC host systems as the third component and eventually resulted in high performance ternary nonfullerene OSCs.The effects of intermolecular interaction between the third component and the host system on device performance were studied in detail.A remarkable enhancement in J_SC(from 14.87 to 18.36 mA cm^-2)was obtained by doping with 10 wt%C7.As a result,the best efficiency of 10.16%was achieved,which exhibited over 35%enhancement compared with the control device without C7?7.50%?.The intermolecular hydrogen bonds between C7 and ITIC can strengthen the electron-withdrawing ability of ITIC,and promote more effective charge transport from PTB7-Th to ITIC.In addition,the hydrogen bonds interaction improvd the morphology and vertical phase separation of the active layer blend,which can enhance photon absorption and increase effective transmission channels.In order to further demonstrate the key role of hydrogen bonds,another dye molecule coumarin 30?C30?,which has similar chemical structures and absorption spectra with C7,was incorporated into the main system to construct ternary OSCs.C30 can not form hydrogen bond with ITIC,as a result,the performance of the ternary device with C30 was not improved.3.The photo-stability,thermal-stability and storage life of the ternary devices doped with TPPI-TPE and C7 were significantly improved.It indicated that the ternary blending method can not only improve the photovoltaic performance,but also enhance the stability of the device,which is of great significance to the practical application of solar cells.In summary,we studied two kinds of small molecular materials that can be used to construct ternary OSCs,and further clarified the internal mechanism of the influence of the third component on device performance,which provided a certain idear for the selection of ternary materials.