Hybrid tandem solar cells with depleted-heterojunction quantum dot and polymer bulk heterojunction subcells

•Hybrid tandem colloidal quantum dot and organic bulk heterojunction solar cells are monolithically connected in series.•Carefully optimized recombination layer of the hybrid tandem solar cells and results in high open circuit voltage and fill factor.•Fill factor of the hybrid tandem solar cells is higher than either of the single-junction subcells.

We investigate hybrid tandem solar cells that rely on the combination of solution-processed depleted-heterojunction colloidal quantum dot (CQD) and bulk heterojunction polymer:fullerene subcells. The hybrid tandem solar cell is monolithically integrated and electrically connected in series with a suitable p–n recombination layer that includes metal oxides and a conjugated polyelectrolyte. We discuss the monolithic integration of the subcells, taking into account solvent interactions with underlayers and associated constraints on the tandem architecture, and show that an adequate device configuration consists of a low bandgap CQD bottom cell and a high bandgap polymer:fullerene top cell. Once we optimize the recombination layer and individual subcells, the hybrid tandem device reaches a VOC of 1.3 V, approaching the sum of the individual subcell voltages. An impressive fill factor of 70% is achieved, further confirming that the subcells are efficiently connected via an appropriate recombination layer.

Graphical abstractHybrid tandem solar cells combining depleted-heterojunction quantum dot and bulk heterojunction polymer:fullerene subcells achieve VOC values of up to 1.3 V that correspond to the sum of the VOC of the individual subcells, and high FFs of ca. 70%. The systematic optimization of the recombination layer allows for an effective connection of the QD and polymer:fullerene subcells in series, resulting in a two-terminal device of particularly high FF values.Figure optionsDownload full-size imageDownload as PowerPoint slide