Efficiency Potential of Rear Heterojunction Stripe Contacts Applied in Hybrid Silicon Wafer Solar Cells

A 2-D numerical analysis evaluating the silicon solar cell efficiency potential of rear-side heterojunction stripe contacts embedded in an AlOx/SiNx passivation stack is presented. Simulated implied efficiencies of correspondingly passivated wafers and device efficiencies of corresponding hybrid solar cells are stated and compared with more conventional solar cell device architectures (i.e., n-PERT and full-area hybrid heterojunction cells). One-dimensional (full-area) and 2-D (stripe contact) lifetime samples are investigated as experimental input for simulation calibration. The influence of the rear-contact area fraction and pitch on both surface recombination and series resistance are investigated. The solar cell efficiency potential (i.e., the implied efficiency) of rear heterojunction stripe contacts is calculated using measured and simulated effective carrier lifetime and series resistance data. For a given (measured) injection-dependent lifetime of the heterojunction and dielectric passivation layers used, the optimum contact geometry (contact area fraction and pitch) is predicted. Assuming either a 1-ms effective lifetime for an ideal a-Si:H(i)/μc-Si:H(p) repassivated lifetime sample (i.e., assuming no laser-induced Si crystal damage due to the contact opening process) or an experimentally observed 300-μs lifetime for an a-Si:H(i)/μc-Si:H(p) repassivated lifetime sample, the calculated 1-sun efficiency potential of rear heterojunction stripe contacts (with optimized rear contact geometry) is 25.8% and 22.9%, respectively. The simulated efficiencies of corresponding hybrid heterojunction cells (having a conventional diffused front-contact system) are 22.7% and 21.4%, respectively. This is significantly higher than the calculated efficiency potential of more conventional solar cell architectures, such as n-PERT cells (20.6%) and full-area hybrid heterojunction solar cells (20.7%).