This deliverable deals with the fabrication of 30%-efficient two-terminal tandem solar cells using Qcells’ (QC) crystalline silicon (c-Si) bottom cells and the perovskite top cells developed at HZB and CSEM. The objective is to fabricate the perovskite-based top cells with scalable processes on a lab-scale, 1-cm² c-Si bottom cells. Based on (dry) vacuum-based perovskite-deposition method using a sequential evaporation approach, HZB fabricated tandem cells with conversion efficiencies still being below the target. In the next steps, HZB will improve the evaporation process and the device integration such as by implementing means of absorber passivation to enhance open circuit voltage and fill factor (FF).

CSEM demonstrated tandem power conversion efficiencies >29% by developing a solution-based perovskite deposition process. Cells made by 1-step blade coating are currently mainly limited by a suboptimal FF. The next steps will involve slightly modifying the perovskite chemistry and its crystallisation to improve FF, the processing of tandems on QC bottom cells, and increasing the active area of the devices. The “hybrid” 2-step method combining thermal evaporation and slot-die coating yields promising single-junction results but requires further improvements to reach the same performance with tandems.