Boosting the Performance of Solar Cells with Intermediate Band Absorbers The Case of ZnTe:O

Abstract

[EN] This work reports on modeling IB (intermediate band) solar cells based on ZnTe:O semiconductor and determination of their photovoltaic parameters using SCAPS (solar cell capacitance simulator) software. A comparative study between photovoltaic performance of ZnTe and ZnTe:O based solar cells has been carried out. It has been found that the energy conversion efficiency ¿, short-circuit current density Jsc, EQE (external quantum efficiency) and FF (fill factor) increased with increasing oxygen doping concentration Nt up to the shallow acceptor density NA and decreased when Nt was higher than NA. The open circuit-voltage Voc remained constant for Nt lower than the acceptor doping concentration NA and decreased for Nt higher than NA. The increase of ¿, Jsc and FF is due to the fact that IB is fully empted, so sub-bandgap photons can be absorbed by hole photoemission process from the VB (valence band) to the IB. The decrease of ¿, Jsc, EQE and FF is attributed to overcompensation for the base doping NA making electron photoemission process from IB to the CB (conduction band) maximized. This indicates that there is a competition between oxygen doping and intrinsic acceptor defects. The optimal concentrations of oxygen and shallow acceptor carriers were found to be Nt ¿ 1015 cm-3 and NA ¿ 1014 cm-3. The corresponding photovoltaic parameters were ¿ = 41.5%, Jsc = 31.2 mA/cm2, Voc = 1.80 V and FF = 75.1%. Finally, the EQE spectra showed a blue shift of absorption edge indicating that the absorption process is extended to the sub-bandgap photons through IB.