Effects of thickness and deposition temperature of ALD ZnO on the performance of inverted polymer solar cells

In this paper, we fabricated atomic layer deposition (ALD) ZnO films to modify indium tin oxide (ITO) electrode for the purpose of the efficient and stable inverted polymer solar cells (PSCs). The role of thickness and the deposition temperature of ZnO layer on the performance of the device was investigated. The results showed that more than 10 nm of ALD ZnO film was required to improve the photovoltaic performance of PSCs. When the deposition temperatures of the ZnO films were varied from 60, 110 to 190 °C, the chemical compositions, the crystal orientations and the mobility of the ZnO films were quite different, while, the work functions of modified ITOs were similar. It was found that the ZnO film could reduce the work function of ITO and turn it into an electron-collecting electrode. The performances of inverted polymer solar cells with the ZnO films deposited at different temperature were identical. We then concluded that the work function of thin ZnO played a crucial role when nano-thickness of ALD ZnO was used as the electron transport layer. As a result, the ALD ZnO films showed a promising interface layer for achieving air-stable plastic cells with roll-to-roll mass production potential.