Invited; Light Induced Degradation in Compensated B-Doped Czochralski Silicon

Light induced degradation (LID) in B-doped Czochralski Si solar cells is a universal phenomenon, which reduces the conversion efficiency by 2-5% relatively. It is believed that Boron-Oxygen complexes are formed during light illumination, which are the effective recombination centers. Studies in the exclusively B-doped Si, B/Ga co-doped Si and p-type B/P compensated Si show that the saturated concentration (N_t*) of B-O defect is proportional to the B concentration (N_B) (or the net hole concentration p₀) and the generation rate constant (R_gen) proportional to p₀². Interestingly, the LID has also been found in n-type B/P compensated Si, which was supposed to be unlikely to happen. Hence, it brings out a fundamental question of whether the p- and n-type B-doped Si have the same formation mechanism of LID.

   In this presentation, we will report our recent work about LID in B-doped compensated Cz silicon. It is believed that the BO defect density in compensated silicon depends on the B concentration and the net doping concentration. Moreover, High B concentration in the compensated silicon results in very serious cell efficiency loss. Furthermore, The electrical parameters of the reference and compensated cells can get fully recovered by illumination at high temperatures.

         Moreover, the LID in n-type B-doped Cz silicon with thermal donors (TDs) compensation is also reported. The advantage of TDs compensation is able to obtain a variation of carrier density but with a constant N_B. We find that the formation of B-O complex also occurs under the light illumination and can be annealed out quickly in the dark at 200 ^oC. The N_t* exhibits a nonlinear dependence on the majority carrier concentrations n₀, and the R_gen is independent on the n₀. The formation activation energy is determined to be 0.4 eV, identical to the value in p-type Si. Based on the results, we believe that the nature of LID in p- and n-type silicon should be the same.