Fabrication And Mechanism Research Of Ternary Organic Solar Cells

Organic solar cells(OSCs)as a clean and renewable energy technology have attracted much attention in the world due to their unique advantages of low cost,light weight,flexibility,large area preparation and abundant raw materials.At present,further enhancement of the performance is still the research focus for the OSCs.In this paper,the increase of photon harvesting for the active layer is the breakthrough piont of the work.Enhancing the power conversion efficiency(PCE)of OSCs by employing ternary strategy is the main purposes.Clarifying the related working mechanism of the ternary OSCs is research emphasis.Not only the photon harvesting range of active layer can be extended by selecting proper materials,but also the ability of photon harvesting of the active layer can be enhanced.The working mechanisms of the ternary OSCs can be clarified by utilizing the characterization means of optics,spectroscopy,morphology,electrical.This paper provides rich experimental results and theoretical analysis for fabricating efficient ternary OSCs in experimental design,material selection,process optimization and mechanism research.The main results and innovations of this paper can be summarized as follows:(1)The ternary OSCs with different systems were studied in this paper.the relationship among the material properties,preparation process,working mechanism and device performance was initial understand.Complementary absorption of the used materials in ative layer is the first requirement for designing ternary OSCs.High extinction coefficient,high carrier mobility,proper energy level aligment and good compatibility also are the important conditions for choosing the third component.Based on the Donor:Donor:PC71BM system,it was proved that the double donor combination of medium band gap:narrow band gap is superior to the combination of wide band gap:medium bandgap.(2)It is proposed that the mechanisms of energy transfer and charge transfer can be distinguished by studying the relationship between the JSC values of the double donor device and the single donor device(no receptor)under the light condition.Combining the variation tendency of PL spectra for the donor solutions and films with different ratio of the third component,the working mechanism of energy transfer and charge transfer can be further revealed.Based on the P3HT:SMPV1 double donor system,the JSC of the device based on P3HT:SMPV1 is much higher than that of P3HT or SMPV1 as the active layer,which indicates that the charge transfer between the two donor materials is dominant working mechanism.(3)It is proposed that the kinetics processes of charge carriers transport in the ternary system can be revealed by studying the variation of the photovoltaic parameters(measured under specific wavelength solar light)for ternary OSCs with different doping ratio of the third component.In the case of PCDTBT:SQ:PC71BM system,the J-V curves of the binary and ternary solar cells were measured under lightillumination with wavelength longer than 670 nm obtained by using a short wavelength cut-off filter.The incident light only can be efficiently absorbed by SQ according to the absorption spectra of used materials.Under this condition,the FF of the ternary OSCs is significantly higher than the value of the SQ:PC71BM cell;when the ratio of SQ in the donors reaches 50 wt%,the JSC of the ternary cells is even higher than that of the SQ PC71BM cell;along with the increase of SQ doping ratio,the VOC of ternary OSCs is almost unchanged,which is close to the VOC of PCDTBT:PC71BM solar cells.The change in the three photovoltaic parameters of the ternary OSCs indicates that the holes in the SQ can be effectively transferred to the PCDTBT and then tansported by means of the hole transport channel formed by PCDTBT.(4)The small molecule ternary OSCs were systematically studied.It is proposed that the kinetics process of energy transfer and charge carrier transport in the ternary system can be clarified by studying the the EQE spectra of devices with planar heterojunction structure.Based on two small molecule DRCN5T and DR3TSBDT with good compatibility as donors in ternary system,the optimized ternary OSCs achieved a PCE of 10.16%,which is one of the highest values for the small molecule ternary OSCs.The main working mechanism of the ternary OSCs is proved to be alloy model by studying the morphology of blend film,the HOMO energy level of materials and the VOC of ternary OSCs.The photon harvesting and interpenetrating network structure can be simultaneously optimized by adjusting the ratios of the two donors.The small molecule ternary OSCs based on the alloy model provides a reference for material selection.(5)Three kind of ternary OSCs based on two non-fullerene receptors were researched.The polymer acceptor N2200 as the third component is incorporated with PBDB-T:I TIC,PBDB-T:I TIC-Th and PBDB-T:IT-M binary system,respectively.The PCE values of the three kind of ternary OSCs are higher than their corresponding binary solar cells.The optimized ternary OSCs based on PBDB-T:IT-MN2200 system achieved a PCE of 12.01%,which is one of the highest values for non-fullerene ternary OSCs.The experimental results show that the performance of the OSCs can be also improved by choosing a polymer receptor as the third component,which extend the application scope of the ternary strategy.