Application of Thin Epitaxial Hydrogenated Si Layers to High Efficiency Heterojunction Solar Cells on N-Type Si Substrates

We show that a thin (<20nm) stack comprised of n(+) doped hydrogenated crystalline silicon (c-Si:H) and n(+) doped hydrogenated amorphous silicon (a-Si:H) can provide an effective back-surface-field for heterojunction solar cells on n-type crystalline silicon (c-Si) substrates. The c-Si:H and a-Si:H layers were grown in the same plasma-enhanced chemical vapor deposition (PECVD) reactor at deposition temperatures close to 200 degrees C. This technique was used to fabricate heterojunction solar cells with open-circuit voltages over 700mV and active-area conversion efficiencies of 21.4% on n-type c-Si substrates.