Photovoltage decay in p-n junction solar cells including the effects of recombinations in the emitter

Abstract

The expressions for the open circuit photovoltage decay in a p‐n junction solar cell are derived, including the effects of recombinations in the emitter. It is shown that for a cell with base thickness w_B≫L_B, the base diffusion length, the voltage decay rate for small values of time depends on the emitter dark saturation current J_E0; the larger the value of J_E0 , the faster is the initial rate of voltage decay. For large values of time, the rate of voltage decay is solely determined by the minority carrier lifetime in the base τ_B and is independent of J_E0 . However, for a cell with w_B≲L_B, the voltage decay is linear from the very beginning and the decay rate is of the form (kT/e)[(1/τ_B) +(1/t₁)]. The time constant t₁ is independent of τ_B . It, however, depends on the base thickness, the effective back surface recombination velocity, and the emitter dark saturation current J_E0 . The value of J_E0 depends on emitter thickness, front surface recombination velocity, drift field in the emitter, band‐gap narrowing, and Auger recombinations in the emitter.