Using a facile processing method to facilitate charge extraction for polymer solar cells†
It is necessary to carefully adjust the interface characteristics between the interlayer and active layer in order to facilitate charge extraction and transfer. Here, a post-annealing treatment on the completed device with a Ag electrode is used to optimize the interface contact characteristics between WO3 and the active layer due to the inter-diffusion of the WO3 hole-extraction interface. The strengthened interface contact between them can improve the charge extraction and transfer across the active layer/WO3 interface. Furthermore, a thinner WO3 interlayer (75 Å) is shown to qualify as an anode interlayer with excellent charge selection, extraction and transport capacities after the post-annealing treatment, which is beneficial for reducing the resistance loss introduced by the too thick WO3 layer and enhancing device performance. As a result, the device with the 75 Å WO3 layer and 60 °C post-annealing treatment provides a higher fill factor of 74.5% and an optimal device performance of 9.66%. This work reveals a simple and universal method to modulate the interface contact characteristics between an evaporated transition metal oxide interlayer and an active layer, thus improving the device performance.