Improved efficiency of organic photovoltaic cells using tris (8-hydroxy-quinoline) aluminum as a doping material

Abstract An improvement of photovoltaic characteristics has been demonstrated in heterojunction organic photovoltaic (OPV) cells with a ITO/copper phthalocyanine (CuPc)/C 60 / bathocuproine (BCP)/LiF/Al configuration by doping tris (8-hydroxyquinoline) aluminum (Alq 3 ) fluorescent dye into the acceptor (or donor) layers. With Alq 3 doping, the short-circuit current density ( J SC ) increased from 8.25 to 12.23 mA/cm 2 , the open-circuit voltage ( V OC ) increased from 0.50 to 0.62 V, and the power conversion efficiency ( η p ) increased from 1.76 to 2.57% under 100 mW/cm 2  AM 1.5 illumination. These improvements can be attributed to the increased light absorption caused by Alq 3 , which led to more effective exciton formation. The energy difference between the highest occupied molecular orbital (HOMO) of the donor and the lowest unoccupied molecular orbital (LUMO) of the acceptor in the doped device increased, leading to a larger V OC . There are no photoluminescence (PL) in the Alq 3 -doped C 60 layer, suggesting that the formation of Alq 3 excitons was followed by energy transfer or charge transfer to C 60 under illumination in the doped layer. The conversion efficiency of OPV cells was thus improved.