Dry fabrication process for heterojunction solar cells through in-situ plasma cleaning and passivation

We have studied low temperature plasma processes (T_sub≤200 °C) for the efficient cleaning and passivation of c-Si wafers, aiming for fully dry fabrication of heterojunction solar cells. We have experimented with H₂-SiF₄ plasmas in a standard RF PECVD reactor in order to etch the native oxide from the c-Si wafer and a thin a-Si:H layer was deposited from SiH₄ to passivate the c-Si surface. In-situ ellipsometry was used to optimize the process conditions for an efficient surface cleaning. Various plasma treatments were performed before a-Si:H deposition in order to reduce the surface recombination. Optimized process conditions resulted in high effective lifetime values (τ_eff≈1.55 ms), low effective surface recombination velocities (S_eff≤9 cm s^-1) and high implicit open circuit voltages (V_oc≈0.713 V).