Efficient Fully-Sprayed Organic Solar Cells with Coffee-Ring-Free Photoactive Layer and Alloy Top-Electrode

Depositing all functional layers (including the top electrode) with spray methods is highly desirable and challenging for the eventual commercialization of organic solar cells (OSCs). This work addresses two key challenges toward fully-sprayed OSCs: i) the printing of a high-quality photoactive layer free of coffee rings and ii) the spray of the top electrode without the need of evaporation nor solvents. To eliminate coffee rings caused by individual droplets, the photoactive layer is deposited by electrospray on the cooled substrate. The reduced temperature slows down the solvent evaporation, promotes merging of individual droplets, and suppresses the formation of coffee rings. By optimizing the drying temperature, homogeneous films without coffee rings are obtained. The improved active-layer morphology facilitates charge transport and reduces recombination. The device prepared by the coldplate-assisted electrospray reaches a power conversion efficiency (PCE) of 17.13%. In addition, an alloy with the melting point of 62 degrees C is spray-printed as the top electrode using an airbrush. The spray process is optimized by the trade-off between the coverage rate and the film thickness. OSCs with the alloy electrode achieve the highest PCE of 16.26%. The fully-sprayed OSCs exhibit PCEs up to 15.09%, demonstrating a viable route toward fully-sprayed OSCs with high-performance.

Automated summary

This work addresses two key challenges toward fully-sprayed organic solar cells (OSCs): the printing of a high-quality photoactive layer free of coffee rings and the spray of the top electrode without the need of evaporation nor solvents. By depositing the photoactive layer using electrospray on a cooled substrate, coffee rings are eliminated, resulting in homogeneous films and improved performance. A spray-printed alloy electrode with a melting point of 62 degrees C is optimized for coverage and film thickness. The fully-sprayed OSCs achieve a power conversion efficiency (PCE) of 15.09%, showing a viable route towards high-performance fully-sprayed OSCs.