Characteristics of sputtered ZnO films for buffer layer in inverted organic solar cells

• Fabrication of zinc oxide films by unbalanced magnetron sputtering.
• Effects of target power density on zinc oxide properties.
• Fabrication of inverted organic solar cells using ZnO film as the buffer layer.
• The maximum power conversion efficiency about 1.99%.

In this work, we describe the characterizations of zinc oxide (ZnO) buffer layers deposited by unbalanced magnetron (UBM) sputtering under various target power densities for inverted organic solar cells (IOSCs). UBM sputter grown ZnO buffer layers exhibited higher crystallinity with increases in target power density, resulting in large grain size, uniform surface morphology, and low resistivity. In addition, it was found that the performance of IOSCs critically depended on the target power density for sputtering of the ZnO buffer layer because the crystalllinity of the ZnO buffer layer affect the carrier mobility of the ZnO buffer layer. For this reason, the IOSC with ZnO buffer layer sputtered at higher target power density showed the better cell performance. Furthermore, we correlated the improved efficiency of the IOSC with the electrical, optical, and structural properties of the UBM sputter grown ZnO buffer layer to design more efficient IOSC with ZnO buffer layer.