Characterization And Optimization Of Binary And Ternary Solar Cells Based On Organic Small Molecules

The energy crisis and the environment crisis are the two major challenges faced by mankind in 21th century.As we all know,the traditional fossil energy not only has just limited reserves but also produces a large number of pollutants when consumed.Therefore,the long-term use of fossil energy in human society has not only led to the lack of available energy,but also aggravated the environmental pollution on the earth.In this case,solar energy has been closely concerned by all mankind because solar energy has the conditions to replace fossil energy with its characteristics of cleaning,non-pollution and inexhaustibility.Organic solar cells have attracted wide attention from all the world because of practical characteristics and processing advantages,such as low cost,easy fabrication,light weight,flexibility and so on.With the joint efforts of researchers in the related fields,organic solar cells are developing rapidly.Solution treatment can be used for the fabrication process of organic solar cells.Compared with the traditional device fabrication process,the fabrication process of organic solar cells is obviously simplified,so it has a very broad application prospect.However,the organic solar cells have not reached the standard of commercial application so far,and further researches on the various aspects of organic solar cells are needed.The devices of organic solar cells based on organic small molecule electron donor were researched in the work of this thesis.Based on the analysis for the research status of organic small molecule solar cells,two kinds of organic small molecular electron donor materials,BDT-OEH and DTBDT-T,have been successfully designed and synthesized and the related properties of these two materials were also tested and studied.Binary organic solar cell devices using the two materials were fabricated respectively.The device properties of organic small molecules as active layer donors and the key factors affecting device performance were studied.The conditions in the fabrication process were optimized and the organic solar cell devices with significant photovoltaic conversion efficiency were fabricated.Then,different concentrations of organic small molecule BDT-OEH were doped into the classical system P3HT and PC₆₁BM,fabricating the ternary organic solar cell devices to study the effect on the performance of organic solar cells when the organic small molecule BDT-OEH served as a supplementary electron donor in ternary system.Compared with the basic binary organic solar cell devices based on P3HT:PC₆₁BM,when the ratio of doped BDT-OEH is 10%,the short-circuit current increased to 9.82 mA/cm²and the filling factor increased to 64.88%.Therefore,the power conversion efficiency of organic solar cells increased 18.65%and reached 3.88%.In the end,ternary organic solar cell devices based on organic small molecule DTBDT-T were fabricated in the same way and the effects of DTBDT-T were studied as a supplementary electron donor on the performance of organic solar cells.The results show that the performance of ternary organic solar cells doped with 5%DTBDT-T is the best.The short-circuit current is 9.93 mA/cm² and the filling factor is 60.17%,the power conversion efficiency of organic solar cells finally reach 3.59%.After data analysis and test verification,it is inferred that the improvement of performance is mainly due to the addition of organic small molecules of appropriate concentration as supplementary electron donor materials.Because the complementary absorption of incident light between different materials broadens the absorption spectra of ternary organic solar cell devices,the photon capture and exciton generation increased.Furthermore,the cascade energy level structure of the ternary organic solar cell devices is conducive to the exciton dissociation and carrier transfer at the donor-acceptor interfaces,and also promotes the transport of free charge carriers in the active layer.The ternary organic solar cell devices with appropriate doping concentration have higher exciton dissociation rate and smoother surface morphology of active layer,which also contributes to the improvement of the device performance.