Abou-Ras, D.; Maiberg, M.: Recombination velocities at grain boundaries in solar-cell absorbers - revisited. Journal of Applied Physics 137 (2025), p. 233106/1-12
10.1063/5.0274267
Open Accesn Version
Abstract:
The present work revisits the recombination velocities (s(GB)) of minority-charge carriers determined at grain boundaries in polycrystalline absorber materials for solar cells. The equations describing s(GB) as well as the barriers for electrons and holes were derived. It is shown that for given net-doping density and absolute temperature, the experimentally determined recombination velocity of a specific grain boundary can be described by s(GB) = s(GB ,0)(n) exp [- Phi(GB) (N-GB ,N- charge) / (k(B)T)], where Phi(GB) is the band bending induced by the excess-charge density N GB , charge at the grain boundary, and k B as well as T are the Boltzmann constant and the absolute temperature; i.e., s(GB) depends only on the excess-charge density at this planar defect as well as on the prefactor s (n)(GB,0) describing the nonradiative recombination. Value ranges for these two quantities can be determined for any measured s(GB) value. When analyzing s (GB) datasets acquired on various (Ag,Cu)(In,Ga)Se-2 and microcrystalline Si absorbers, it is apparent that both the excess-charge density and the prefactor s(GB ,0)(n) remain within about the same orders of magnitude for all grain boundaries analyzed in a specific absorber. The broad range of the recombination velocities over several orders of magnitude indicates upward as well as downward band bending, and the band-bending values are on the order of several +/- 10 meV for all materials analyzed.