Light-induced Degradation In Efficiency Of Crystalline Silicon Solar Cell

The efficiency of commercial solar cells is further closing to the laboratory record withthe progress in crystalline silicon solar cells. The quality of silicon wafers is a limitingfactor for the improvement of solar cell efficiency which is decided by the impurities anddefects in crystalline silicon. P-type boron-doped (B-doped) Czochralski silicon (Cz-Si)usually suffers the light-induced degradation (LID) in efficiency. Improving the quality ofCz-Si and researching the method and mechanism of suppressing LID have become theimportant topic in photovoltaic field.1. The annealing behavior of impurities and defects in Ga-doped and B-doped Cz-Si andthe effect of annealing on the minority carrier lifetime (τ) were studied. During one-stepannealing process, the isochronal annealing results showed that the interstitial oxygenconcentration ([Oi]) and the minority carrier lifetime decreased, but the etched pits density(EPD) induced by oxygen precipitations increased both in Ga-and B-doped Cz-Si with theincreasing of annealing temperatures. It is also shown that the [Oi] decreased moreobviously in Ga-doped Cz-Si and the size of etched pits in Ga-doped Cz-Si was smallerthan that in B-doped Cz-Si. And the [Oi] decreased faster at lower temperature annealing.The isothermal annealing results showed that [Oi] decreased and EPD increased both in Ga-and B-doped Cz-Si, but the minority carrier lifetime changed very little with the annealingtime extending. During two-step annealing process, decreasing rates of [Oi] and τ werefaster with the raising of the second step annealing temperatures both in Ga-and B-dopedCz-Si.2. The performance of Cz-Si wafers with Ga and B co-doping and solar cells fabricatedwith these crystalline silicon wafers were investigated. The results showed that τ in100%Ga-doped Cz-Si was twice as high as that in100%B-doped Cz-Si and lower in Ga and Bco-doped Cz-Si wafers. The efficiency of solar cells fabricated with different ratios ofGa-doped Cz-Si achieved the level of solar cells with100%B-doped Cz-Si, and there was ahighest efficiency when Ga-doped ratio was80%.3. The effect of Ga-doped ratio on the LID in efficiency of solar cells was investigated. Itis shown that LID rate decreased with the increasing of Ga-doped ratios. And the minimumLID rate,0.205%, was obtained when Ga-doped ratio was100%. The LID in solar cells fabricated with Ga-doped Cz-Si was suppressed by the reducing of B-O complexes due tothe doping of Ga atoms.