Design And Improvement In OPV Cells Based On New Type Organic Interlayers

Organic photovoltaic(OPV) cells have the advantages of low cost, light weight, flexible, simple preparation, etc., which are expected to become a new kind of green energy in the future. However, the power conversion efficiency(PCE) of OPV cells is still lower than that of inorganic counterparts. Thus it is necessary to further improve the performance of OPV cells. Interfacial modification of OPV cell is a simple way to improve their performance. The main research works of this thesis are to design new anode interface layers and to improve the performance of OPV cells. The main contents of are listed as follows:(1) We have fabricated a new OPV cells with rubrene and Sub Pc as the donor and acceptor, respectively. Due to the large difference between the highest occupied molecular orbital(HOMO) of the donor rubrene and the lowest unoccupied molecular orbital(LUMO) of the acceptor Sub Pc, a very high open-circuit voltage of 1.45 V is obtained. The performance of the device strongly depends on the thickness of rubrene, and a highest PCE of 2.52% under simulated AM1.5 G solar illumination at 100 m W/cm2 is realized at a thickness of rubrene as thin as 5 nm. Besides, the device also shows a superior stability compared to traditional device with C60 acceptor.(2) We have constructed a new organic hetero-interface layer which consists of a electron-transporting layer(ETL) and hole-transporting layer(HTL). Improved PCE is found in the planar heterojunction OPV cell with a structure of ITO/Cu Pc/C60/Bphen/Al when this organic hetero-interface layer is inserted between ITO anode and Cu Pc layer. The device with a F16 Cu Pc(3nm)/TAPC(3 nm) hetero-interface layer shows a PCE of 1.67%, which is 1.64 times to that of the device without anode buffer layer and 2.98 times to that of the device with a single TAPC layer as the anode buffer layer. It is found that the hole extraction process is actually a electron-hole recombination process with electrons injected from ITO anode and holes extraction from Cu Pc. Besides, the property of this organic hetero-interface layer strongly depends on the energy difference between the HOMO level of HTL and LUMO level of ETL, and the optimized difference is found to be about 0.6 e V.(3) We used Sub Pc as the anode interlayer for the bulk heterojunction OPV cell with low donor concentration. The device has a structure of ITO/Mo O3(5 nm)/ Sub Pc/C60:5 wt% TAPC/BCP/Al. A maximum PCE of 3.75% is found for the device with a 5-nm-thick Sub Pc, which is increased of about 35.4% compared with the reference cell without Sub Pc. Besides, the Voc of the device is also increased. It is found that Sub Pc has no contribution the response the optimized device. On contrast, the response of C60 is increased significantly. The improvement is attributed to the increased build-in field of the device due to the interaction between Mo O3 and Sub Pc.