Device Fabrication And Performance Studies For Igh-efficiency Organic Solar Cells

Organic solar cells(OSCs)have emerged as a promising photovoltaic technology due to the advantages of high power-to-mass ratio,simple fabrication process,and excellent applicability for flexible devices.Power conversion efficiency(PCE)is a key parameter to evaluate the performance of various OSCs,and it is also an important basis for evaluating the industrialization value.Currently,the PCE of single junction OSCs has exceeded 19%.OSCs are in the critical stage of transferring research results to production.It is the key to accelerate the industrialization of OSCs that further improves the PCE of the OSCs based on high-efficiency photovoltaic materials combined with device process optimization.In this dissertation,various high-performance OSCs are prepared by optimizing the device processing technology to adjust the ink characteristics and morphology evolution as well as photoelectric properties of the active layer.Moreover,we further deeply investigate the structure-performance relationship between morphology characteristics,charge transfer and device performance.The main contents and results are as follows:(1)The ternary strategies are utilized for improving the photovoltaic performance of single-junction OSCs.A wide bandgap nonfullerene acceptor named AITC is synthesized and introduted into PM6:BTP-eC9 system.AITC exhibits a good complementary absorption spectrum with the narrow bandgap acceptor BTP-eC9.AITC also shows good miscibility with BTP-eC9,which facilitates the formation of a stable mixing phase in the blends.Moreover,the large dipole moment of AITC with asymmetric molecule structure reinforces the molecular packing in the blend film of PM6 and BTP-eC9,thereby enhancing the photoconductivity,suppressing charge recombination and reducing non-radiative voltage loss in the ternary OSCs.As a result,the ternary OSCs based on PM6:BTP-eC9:AITC achieve an outstanding PCE of 18.8%(18.4%±0.4%).In addition,the tandem OSCs using PM6:AITC as the bottom sub-cell and PM6:AITC:BTP-eC9 ternary active layer as the top sub-cell exhibit a remarkable efficiency of 19.4%(18.96±0.3%).(2)In terms of tandem OSCs,we change the weight ratio of donor and acceptor(D/A)as well as film thickness in active layer to regulate the optical distribution of the sub-cell,and further investigate their influence on film morphology and charge transport properties under the real incident light in the sub-cell.The tandem OSCs studied are constructed with the device structure of indium tin oxide(ITO)/ZnO/bottom photoactive layer/interconnecting layer(ICL)/top photoactive layer/MoOx/Ag,where the bottom and top photoactive layers are based on blends of PM6:ITCC and PM6:BTPeC11,respectively,and ICL refers to interconnecting layer structured as MoOx/Ag/ZnO:PFN-Br.By rationally modulating the composition and thickness of PM6:BTP-eC11 blend films,a clear red-shift of the absorption edge and enhancement of the absorption coefficient are shown in the acceptor absorption response range.The 300 nm-thick PM6:BTP-eC11 film with 1:2 D/A weight ratio is found to be an ideal photoactive layer for the top sub-cell in terms of photovoltaic characteristics and light distribution control.As a result,the single-junction OSCs with the optimal BHJ film still maintain a low recombination rate and defect state density under the real incident light of the top sub-cell.For the best tandem OSCs,a PCE of 19.6%(18.9%±0.4%)is realized,which is the highest result in the OSCs field.(3)In terms of large area OSCs,we investigate the coating conditions and ink composition in dip coating and their influence on the fluid mechanics,film formation kinetics,micromorphology,charge transfer and device performance of the OSCs.We demonstrate the correlations between the fluid characteristics and the BHJ morphologies by employing the five coating conditions.As a result,the shearing effect in shearing region,the capillary number of the liquid in laminar flow region can be tuned,which significantly affect aggregation conformation of the polymer phase and continuity of the small molecular phase.Similarly,we optimize the dip coating conditions of the anode and cathode interface layers(PEDOT:PSS and PDINN),respectively,so as to fabricate the all-printed OSCs.For the 1 cm2 rigid cells,the best PCE of 17.9%(17.5%±0.2%)is recorded.For large area coating,we get the PCEs of 15.1%(14.7%±0.3%)and 13.7%(13.4%±0.3%)for the 10 cm2 rigid and flexible cells,respectively,which are the top values in the field.In addition,benefiting from the superiority of dip coating that can be performed on the curved surfaces,we are able to fabricate the OSCs on the copper rods,demonstrating the feasibility of making OSCs on any conductive surface.