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Effect of dislocations on minority carrier diffusion length in practical silicon solar cells

: Kieliba, T.; Riepe, S.; Warta, W.


Journal of applied physics 100 (2006), Nr.6, Art. 063706, 12 S.
ISSN: 0021-8979
ISSN: 1089-7550
Fraunhofer ISE ()

In 1998, Donolato presented an analytical model describing the effect of dislocation density on minority carrier effective diffusion length [J. Appl. Phys. 84, 2656 (1998)]. While this analysis was derived for a "semi-infinite" specimen, our objective is the appropriate description of thin devices, such as wafer or thin-film based crystalline Si solar cells with back surface field or passivating layer on the rear side. Therefore, Donolato's model is extended for specimen of finite thickness and finite recombination velocity at the back surface. Since the associated boundary value problem does not allow a straightforward analytical solution, we derive an approximate expression, which is validated by numerical simulations. In the original work, Donolato uses a special definition of an "effective diffusion length." This definition is different from the quantity usually referred to as effective diffusion length when analyzing quantum efficiency data. Furthermore, Donolato's definition does not refer to the typical operation conditions of a solar cell. We therefore modify Donolato's model for the effect of dislocations consistently using the quantum efficiency effective diffusion length. Finally, our model is applied to the determination of dislocation recombination strength in thin-film solar cells with back surface field from effective diffusion length maps.