Progress in Silicon Heterojunction Devices by Hot-Wire CVD: Preprint

We report on fabrication of silicon heterojunction (SHJ) solar cells based on Al backed p type silicon wafers, with hot-wire chemical vapor deposition (HWCVD) hydrogenated amorphous silicon (a-Si:H) emitter layers. The two-layer emitters are comprised of an extremely thin (~5-nm) intrinsic a-Si:H (a-Si:H(i)) layer topped with a slightly thicker phosphorous-doped a Si:H layer (a-Si:H(n)).Open-circuit voltages (Voc) above 620 mV are routinely achieved with a maximum of over 640 mV, indicating effective passivation of the crystalline silicon (c-Si) surface by the thin a Si:H(i/n) stack. We used real-time spectroscopic ellipsometry (RTSE) as an in-situ diagnostic tool to monitor film thickness and roughness in real-time and to observe silicon crystallinity by further ex-situ dataanalysis. The deposited films were also examined by high-resolution transmission electron microscopy (HRTEM). Immediate a-Si:H deposition and a flat interface to the c-Si is the key factor in obtaining high Voc. On commercial p type B-doped Czochralski silicon (CZ-Si) wafers with a polished surface and 2.1 ohm cm resistivity, the best efficiency obtained is 14.8%. Efficiency above 15.7% isachieved on a 1.3 ohm cm, p-type B-doped float-zone silicon (FZ-Si) wafer with a chemically polished front surface and a screen-printed Al-BSF.