Diode Characteristics in State-of-the-Art ZnO/CdS/Cu(In1-xGax) Se2 Solar Cells

We report a new state of the art in thin-film polycrystalline Cu(In,Ga)Se₂-based solar cells with the attainment of energy conversion efficiencies of 19·5%. An analysis of the performance of Cu(In,Ga)Se₂ solar cells in terms of some absorber properties and other derived diode parameters is presented. The analysis reveals that the highestperformance cells can be associated with absorber bandgap values of ∼1·14eV, resulting in devices with the lowest values of diode saturation current density (∼3 χ 10^-8 mA/cm²) and diode quality factors in the range 1·30 < A < 1·35. The data presented also support arguments of a reduced space charge region recombination as the reason for the improvement in the performance of such devices. In addition, a discussion is presented regarding the dependence of performance on energy band-gap, with an emphasis on wide-bandgap Cu(In,Ga)Se₂ materials and views toward improving efficiency to >20% in thin-film polycrystalline Cu(In,Ga)Se₂ solar cells. Published in 2005 by John Wiley & Sons, Ltd.