Modelling of transport and recombination of photoexcited carriers in a-Si:H and a-SiGe:H

The modeling of transport and recombination of photoexcited carriers generated by low bandgap light has been performed to simulate photoconductivity, σ_ph, in a-Si:H and a-SiGe:H solar cells, versus illumination, φ, and temperature, T. For the occupation of states in the gap, rates for trapping, recombination, and remission have been solved by detailed balance: for charge transport, only the extended states contribution is considered. The influence on σ_ph(φ,T) of characteristic energies of band tails has been analyzed as well as of densities of midgap states, which have been treated by two different approaches: by the conventional defect model (CDM) with D⁺/D⁰ at an E_c of 1.0 eV and D at an E_c of 0.6 eV; and by the novel defect pool model (DPM), introducing three differently charged defects. No dramatic difference in σ_ph is observed for both recombination models: however. DPM is superior to CDM, in that a more realistic correlation energy of +0.2 eV can be applied and fine structure in σ_ph vs. T can be achieved