Improvement in open circuit voltage of organic solar cells by inserting a thin phosphorescent iridium complex layer

The authors develop organic solar cells (OSCs) with a multicharge separation (MCS) interface by inserting similar to 4 nm thin layer of phosphorescent bis(2-(4- tertbutylphenyl) benzothiazolato-N,C(2)) iridium (acetylacetonate) (t-bt)(2)Ir(acac) comparing with copper phthalocyanine (CuPc) between pentacene/C(60) heterojunction. The result showed that open circuit voltage is remarkably enhanced without obviously changing external quantum efficiency eta(EQE) and short-circuit current density. As a result, power conversion efficiency is improved from 1.53% for pentacene/C(60) device to 1.83% with sandwich layer (t-bt)(2)Ir(acac) and 1.98% with CuPc. Moreover, a suitable equivalent circuit model is proposed to intuitively reveal the inner photogeneration process of OSC with MCS interface. (C) 2010 American Institute of Physics. [doi:10.1063/1.3492838]