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

Wednesday, 8 October 2014: 11:40
Expo Center, 1st Floor, Universal 17 (Moon Palace Resort)
D. Yang (Zhejiang University, State Key Lab of Silicon Materials)
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 (Nt*) of B-O defect is proportional to the B concentration (NB) (or the net hole concentration p0) and the generation rate constant (Rgen) 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 NB. 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 Nt* exhibits a nonlinear dependence on the majority carrier concentrations n0, and the Rgen 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.