I was involved in the project of designing an efficient quantum dot intermediate band (QD IB) solar cell.

The QD IB solar cell is modeled in SILVACO ATLAS to investigate the contribution of every possible secondary effect in failure to reach its analytically predicted efficiency of around 40%.

Firstly, a three level model of the QD IB solar cell is developed using the acceptor type trap states to simulate the effects of QD to create an intermediate band. Simulation using absorption coefficient of 10⁴ cm-1 and drift-diffusion transport neglecting secondary effects reveals an efficiency of 39% for optimal IB filling of 0.1. However, incorporation of the wavelength dependence of extinction coefficient derived from SOPRA database reduces the efficiency to around 22% due to lowering of short circuit current. Moreover, taking Shockley-Read-Hall, Auger and surface recombination into account and specifying the doping - and temperature-dependent low-field mobilities using Caughey-Thomas formula, along with considering non-local transport effects by means of energy balance transport the efficiency is found to be no more than 12%. Field and doping dependence of the mobilities results in the majority of the degradation in efficiency (22%) while Auger and surface recombination as well as bandgap narrowing have trivial effects on the performance parameters. On the other hand, Shockley-Read-Hall recombination causes almost 8% reduction in efficiency.

Furthermore, to investigate the secondary effects of QD IB solar cell in a more rigorous way, a four-level model is developed using acceptor type trap states near the conduction band and donor type trap states near the valence band in IB region. This four level model predicts further 29% reduction of efficiency.