Investigation On The Small Ratio Donor Organic Bulk Heterojunction Photovoltaic Cells

Organic photovoltaic(OPV) has garnered significant attention all over the world as a result of their potential low cost, light weight, high tunability, easy fabrication over large and flexible substrates. Nowadayes for the purpose of commercial application OPV studies mainly concentrate on improving the power conversion efficiency(PCE), lifetime and stability.This work focuses on the study of small molecule organic bulk heterojunction devices, including the following contents:First, small ratio of phosphorescent material was adopted as donor component to fabricate organic photovoltaic(OPV) cells with structure of the Mo O3/5% wt. Ir(ppy)3: C60. Through fabricating OPV devices with different thickness of anode buffer layer Mo O3, the relationship between the Mo O3 thickness and the open-circuit voltage as well as the short circuit current was analyzed. Moreover, we inserted C60 layer between active blend layer and cathode buffer and optimized the thickness of C60 layer. Thus an optimal device structure was obtained with PCE of 1.75 %. Finally, using C70 with more intensive absorption to replace the acceptor component of C60, PCE was dramatically improved from 1.75% to 3.01%.Second, through inserting a p-type material of 4,-4’-Bis(carbazol-9-yl)-biphenyl(CBP) as an exciton dissociation and blocking layer(EDL/BL) in optimized device, resulting a notable 33% increase of PCE from 1.75% to 2.31%. Through optical simulation and film photoluminescence(PL) spectra, the mechanism explores of EDL/BL is studied. By selceting different p-type materials in devices, it was found that the hole mobility of EDL/BL as well as their energy levels had a crucial effect on the performance of OPV cells. Employing CBP as EDL/BL, C70 with wider and more intensive absorption as acceptor instead of C60, PCE of 3.96% was obtained.