Exfoliated, thin, flexible germanium heterojunction solar cell with record FF=58.1%

A thin, flexible monocrystalline germanium (c-Ge) heterojunction solar cell has been developed based on a novel kerfless exfoliation process and remote plasma-enhanced chemical vapor deposition (RPCVD) of hydrogenated amorphous silicon (a-Si:H). The performance of the exfoliated 50 μm thick and bulk 500 μm Ge heterojunction cells is compared in this paper. A superior conversion efficiency of 5.28% was achieved with the 50 μm exfoliated Ge cell versus 1.78% for the bulk Ge cell, in agreement with simulation results. A record fill factor of 58.1% for an a-Si:H/c-Ge heterojunction cell was obtained with the exfoliated cell. Moreover, the conversion efficiency achieved with the 50 μm exfoliated cell (without intrinsic a-Si:H passivation) is comparable to the best reported in literature with bulk Ge heterojunction cells and intrinsic a-S:H passivation.

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► A novel kerfless exfoliation process is used to realize a thin, flexible and mechanically robust Ge foil.
► a-Si:H/c-Ge heterojunction cells on the exfoliated Ge foil and bulk 500 μm Ge substrate are fabricated using a remote plasma CVD system without i-layer.
► Exfoliated, thin Ge cell shows a superior efficiency of 5.28%, compared to 1.78% for the bulk Ge cell, in agreement with simulation results.
► A record fill-factor of 58.1% for an a-Si:H/c-Ge heterojunction cell is obtained with the exfoliated Ge cell.