Construction and characteristics of tandem organic solar cells featuring small molecule-based films on polymer-based subcells

In this study, we stacked a small molecule-based cell onto another polymer-based device to fabricate a tandem organic solar cell that extended the absorption range of the entire cell over a wider spectral range. Between the two subcells, we positioned a connecting structure comprising layers of Cs 2 CO 3 , Ag and MoO 3 . Current matching phenomena played an important role in determining the device efficiency. The judicious selection of subcells exhibiting superior current matching improved the performance of the tandem cell. Indeed, in the optimally performing tandem cells we obtained both a high open-circuit voltage (1.21 V) and an improved power conversion efficiency (1.81%). From analyses of the surface morphology and transmission spectra of the middle Ag layers, we deduced that the main function of this film was to provide more sites for efficient recombination of holes and electrons. The thickness of this layer was limited by its transmittance. A thinner Ag layer allowed more light to be harvested by the top cell, increasing the overall performance of the tandem cell.