Doping dependence of surface and bulk passivation of multicrystalline silicon solar cells

The base doping level of solar cells is an inexpensively adjusted parameter. To make an informed selection of doping level, we must know the doping dependence of bulk lifetime (τ_b) and surface recombination velocity (S). The doping dependence of τ_b and S in string ribbon and cast multicrystalline silicon (mc-Si) is investigated in this research using a combination of device modeling, the derivation of useful and pertinent equations, and experiments based on test structures and complete devices.; Experimentally, investigators frequently make effective-lifetime (τ _eff) measurements that satisfy quasi-steady-state conditions. In fact, these are the conditions most frequently encountered when working with low-cost, solar-grade materials. Surprisingly, the steady-state relationship among S, τ _b, and τ_eff has not appeared in the literature. Therefore, we derive the steady-state relationship among S, τ_b, and τ _eff for illumination of arbitrary spectral content. We show that the steady-state equation is the only equation that matches the general equation over the entire range of τ_eff for slowly decaying illumination, but any equation may be used when τ_eff > 20 μs. When τ_eff < 10 μs and a popular flash lamp is the illumination source, the steady-state equation derived in this research must be used to avoid error that can exceed 100%.; Having established the correct relationship among measured τ _eff and the two parameters of interest, S and τ_b, techniques for separating the effects of S and τ_b on τ_eff are investigated. We confirm that the conventional method of iodine passivation can reduce S below 2 cm/s on float zone; however, we demonstrate for the first time that the same iodine solution can fail to passivate low-cost materials well enough to determine S for a dielectric. Additionally, a sensitivity analysis is performed to show that a two-spectrum method to obtain information about τ _b and S has serious limitations: only a lower bound can be placed on τ _b for τ_b greater than about 10 μs, and only an upper bound can be placed on S for S less than about 1000 cm/s.