The effects of copper phthalocyanine purity on organic solar cell performance

The performance of small-molecular weight organic double heterojunction donor-acceptor bilayer solar cells is studied as a function of the purity of the donor material, copper phthalocyanine (CuPc). We find that the power conversion efficiency under simulated AM1.5G, 1 sun illumination conditions increases from (0.26 +/- 0.01)% to (1.4 +/- 0. 1)% as the CuPc layer purity increases. Concomitant with the improvements in power conversion efficiency, we find that the hole mobility of the unpurified CuPc is nearly three orders of magnitude lower than for purified source material. Mass spectrometry and Fourier transform infrared spectroscopy are used to identify metal-free phthalocyanine as the primary impurity that degrades both device efficiency and hole mobility. (c) 2005 Elsevier B.V. All rights reserved.