Cat-CVD deposited inverted μc-Si:H/c-Si heterojunction solar cell approach

Catalytic chemical vapor deposition (Cat-CVD), is a new technology to obtain device-quality thin films at low substrate temperatures. In the other hand, the inverted microcrystalline-silicon/crystalline-silicon (muc-Si/c-Si) hetero-junction, consists of a solar cell illuminated on the backside, the c-Si part of the hetero-structure. This, structure configuration avoids the light absorption in the heavily-doped emitter (dead-layer) and also eludes the use of transparent conducting oxide (TCO) on the emitter. If the back-surface is properly treated, this structure has the advantage to absorb major part of the solar spectrum. Very thin intrinsic hydrogenated amorphous silicon (i-a-Si) as a buffer-layer, and boron-doped hydrogenated microcrystalline silicon (p-muc-Si) were deposited using Cat-CVD system on crystalline-silicon (c-Si) substrate. Solar cells were fabricated on Czochralsky (CZ)-grown phosphorous-doped c-Si within 0.5 to 1 ohm-cm. The tungsten catalyst temperature (T_fil) was settled to 1600 degC and 1950 degC for i-a-Si and p-muc-Si films, respectively. Silane (SiH₄) and hydrogen (H₂) gases were used and diluted diborane (B₂H₆) for p-doping at the substrate temperatures (T_sub) of 200 degC. The preliminary I-V characteristics under natural solar radiation and corrected to 100mW/cm² are: Jsc =25.9 mA/cm²; Voc = 480 mV; Jm = 19.24 mA/cm²; Vm = 320 mV; FF = 49.5%. Being an active area efficiency of etan= 6.15%.