Impact of the energy difference in LUMO and HOMO of the bulk heterojunctions components on the efficiency of organic solar cells

The characteristics of two bulk heterojunctions photovoltaic devices composed of zinc phthalocyanine (ZnPc) as electron donor and as electron acceptor, for which we used perylene tetracarboxylic dianhydrid (PTCDA) or 1, 4-diaminoanthraqui none (1,4-DAAQ) having been studied. Organic semiconductor-blended films were formed by highvacuum co-evaporation. To study the properties of the different samples, the films were characterized by optical absorption, scanning electron microscopy (SEM) measurements, and solar cell I-V measurements, AM1.5 (1000W/m(2)) irradiance. Theoretical and experimental results have shown that a better efficiency is obtained in blending ZnPc with PTCDA more than with 1,4-DAAQ. The offset of the band edges of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the blended components will prove responsible for the improvement of all photovoltaic properties of the organic solar cells. (C) 2007 Elsevier B.V. All rights reserved.