Development and understanding of the intrinsic and doped amorphous emitter-layer stacks for silicon heterojunction solar cells
Comparison of the open-circuit voltage Voc determined by sunsVoc to the implied voltage Voc,impl determined by transient QSSPC lifetime measurements can lead to a quick and easy analysis and characterization of silicon heterojunction (SHJ) solar cells, especially in regard to finding the optimum doping concentration of the emitter layer (stack system). The Voc,impl represents the interface passivation quality. The sunsVoc value gives us additionally a measure of the apparent band-bending. Increasing the concentration of doping gases during the deposition of e.g. a-Si:H(p) reduces the interface passivation quality (Voc,impl) and increases the band-bending (sunsVoc value). The best trade off is realized when the ratio of sunsVoc to Voc,impl (Voc trade off ) first comes to a saturation value near 1, while increasing the doping concentration. For a-Si:H(p) layers the pseudo fill factor PFF is found to be dependent on the doping concentration, too. Thus, the maximum value obtained for the PFF sunsVoc product is taken as a measure for the optimal doping concentration of a-Si:H(p) emitter layers. This approaches are applied to answer the following questions: i) what is the optimum doping concentration for an a-Si:H(n) emitter layer vs. an a-Si:H(i & n) emitter layer stack? ii) what is the best doping concentration of the a-Si:H(p) layer in an a- Si:H(i & p) emitter layer stack system including a variation of the a-Si:H(i) as well as the a-Si:H(p) layer thickness?