Utilizing Metal Oxide Thin Films for Device Engineering of Solution-Processed Organic Multi-Junction Solar Cells

Abstract

Electron and hole transporting layers play a major role in high-performance and stable organic-based optoelectronic devices. This paper demonstrates detailed device engineering of multi-junction organic photovoltaics built on two different metal oxide-based electron and hole transport (buffer) layers prepared by thermal or solution-processed methods. The main focus is on the device processing parameters as well as practical details of preparation of buffer layers to give the research community a clear, step-by-step recipe to successfully replicate and build series and parallel connected multi-junction solution-based organic solar cells for their needs. Here, the recipes and deposition conditions of two metal oxide buffer layers are presented in detail, based on basic commercially available materials and tools, to achieve well-engineered tandem (multi-junction) solution-processed organic solar cells. The buffer layers have appropriate energy levels for electrical selectivity of anode and cathode electrodes, and they are highly stable and chemically compatible with processing of solution-based polymer solar cells. To demonstrate the engineering steps of multi-junction devices, the PCE10:PC70BM blend is used as the active layer for all subcells. Then, to improve the power conversion efficiency of the single-junction photovoltaic device, PCE10:PC70BM blend is used in combination with DPPx:PC70BM with different absorption spectra for bottom and top subcell active layers. An optimized series tandem device with 10.6% power conversion efficiency is demonstrated. Generally, the device structures reported here can also be used for other types of optoelectronic devices, such as light emitting diodes and photodetectors.