Efficient hybrid inorganic/organic tandem solar cells with tailored recombination contacts

• 7.5% efficient hybrid inorganic/organic tandem solar cells are presented.
• Tandem cells are made of a-Si:H bottom cells and Si-PCPDTBT:PC70BM bulk heterojunction top cells.
• Loss-free recombination contacts are realized with a FF of 70% and a Voc close to the sum of those of the sub-cells.
• Optical and electrical device modeling suggests 12% efficiency when combining a donor with suitable absorption onset.
• Proof-of-principle studies employing light trapping suggest that efficiencies well above 12% can be potentially achieved.

In this work, the authors present a 7.5% efficient hybrid tandem solar cell with the bottom cell made of amorphous silicon and a Si-PCPDTBT:PC70BM bulk heterojunction top cell. Loss-free recombination contacts were realized by combing Al-doped ZnO with either the conducting polymer composite PEDOT:PSS or with a bilayer of ultrathin Al and MoO3. Optimization of these contacts results in tandem cells with high fill factors of 70% and an open circuit voltage close to the sum of those of the sub-cells. This is the best efficiency reported for this type of hybrid tandem cell so far. Optical and electrical device modeling suggests that the efficiency can be increased to ~12% on combining a donor polymer with suitable absorption onset with PCBM. We also describe proof-of-principle studies employing light trapping in hybrid tandem solar cells, suggesting that this device architecture has the potential to achieve efficiencies well above 12%.