Donor–acceptor nanocomposite structures for organic photovoltaic applications

We investigated the effect of substrate temperature T S on the growth of 80 nm donor–acceptor nanocomposite (DAN) layers consisting of co‐evaporated Zn‐phthalocyanine (ZnPc) and C 60 as absorber materials in organic solar cells. High temperature devices show lower series resistances R S but also reduced V OC . Both effects are diminished when the upper 20 nm of the blend are deposited at room temperature (RT). Moreover, the temperature profile improves the photocurrent density J SC . Best efficiencies (up to 2.1%) were achieved applying a 90 °C/RT profile. Transmission electron microscopy studies on the corresponding DAN revealed the temperature‐dependent formation of crystalline C 60 phases (already at low T S ) and crystalline ZnPc phases (at highest T S ). The strong phase separation at 90 °C results in less compact and mechanical unstable films. Such devices exhibit low parallel resistance R P . When the cold cover layer is applied R P doubles.