Toward film-silicon solar cells on display glass

We describe recent progress in developing epitaxial film crystal silicon (c-Si) solar cells that can be grown at low temperature (<760 °C) on seed-on-glass substrates. This low-cost approach is enabled by rapid epitaxy (up to 300 nm/min) of Si films with low dislocation density (< 1×105 cm⁻²) at glass-compatible temperatures by hot-wire chemical vapor deposition (HWCVD). Epitaxial test cells on heavily-doped ‘dead’ Si wafers provide insight into the quality of the Si absorber and the physics that limit device performance. Our best 2–3 µm thick, film silicon heterojunction (c-Si/a-Si) solar cells have reached ∼6.7% efficiency (Voc ∼ 570 mV, Jsc ∼18 mA/cm⁻²) without rapid thermal anneal, defect passivation or light trapping. Unpassivated dislocations are strong recombination centers and limit effective minority carrier diffusion lengths to less than 15–20 µm (roughly half the distance between dislocations). We also report devices without light-trapping on layer-transfer Si seed layers bonded to display-glass; these seed layers template growth of high-quality HWCVD cSi. Our initial devices have Voc = 460 mV, Jsc = 16.2 mA/cm², Eff. = 4.8 %, but will benefit from post-growth anneals, hydrogenation and new surface treatments before epitaxy. We discuss junction transport physics in the devices and explore the role of post-growth H-passivation and rapid thermal annealing treatments on device performance.