Effects of ZnO fabricating process on the performance of inverted organic solar cells

The effects of zinc oxide (ZnO) fabricating process on the performance of the inverted bulk heterojunction (BHJ) solar cells were explored in this study. The ZnO layers were prepared by either sputtering or solution-processed method. These ZnO films on the indium tin oxide (ITO) substrates were used as the cathode of the inverted solar cells. It was found that the topography of the ZnO films played a leading role on the device performance. The devices based on solution-processed ZnO films displayed better electric output compared with that of sputtered ones. The measurement of capacitance against bias voltage indicated that ZnO film with certain degree of roughness exhibited high charge extraction efficiency, which resulted in improved device performance. The measurement of ultraviolet photoelectron spectroscopy revealed that a shift of work function was observed due to the fabricating process of ZnO films.

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► ZnO films with various morphologies achieved by several fabrication methods.
► ZnO films with different work function if fabricated by various methods.
► Both topography and work function of ZnO film effecting device performance.
► Capacitance measurement indicated roughness dominating device performance.