InGaN/Si heterojunction tandem solar cells

Tandem solar cells using InxGa1-xN heterojunctions with silicon as the active junction were fabricated using gas-source molecular beam epitaxy (MBE) and by a novel deposition method incorporating an energetic nitrogen atom source. N-type InGaN layers were grown on p-Si(111) to evaluate predicted low-resistance tunnel junction properties. Ohmic behavior was observed, showing that these junctions can be used to connect the two pn subcells of an InGaN/Si tandem without the requirement of the heavily doped layers used in current multijunction cells. Undoped and Mg-doped films were grown by MBE on n-Si(111) using a AlN buffer layer. Depletion is observed on the Si side of the junction and efficiencies approaching 5% were measured for this “hybrid” cell design. Conditions for achieving depletion on the p-InGaN and producing a “single-junction” tandem cell are discussed.