Open circuit voltage recovery in GaAsSbN-based solar cells: Role of deep N-related radiative states

• Published in: Solar energy materials and solar cells Vol. 200; p. 109949
• Main Authors: Gonzalo, Alicia, Stanojević, Lazar, Utrilla, Antonio D., Reyes, Daniel F., Braza, Verónica, Fuertes Marrón, David, Ben, Teresa, González, David, Hierro, Adrián, Guzman, Alvaro, Ulloa, José María
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15-09-2019; Elsevier BV
• Subjects: Annealing; Defect annealing; Energy gap; GaAsSbN; Growth rate; Molecular beam epitaxy; Multi-junction solar cells; Open circuit voltage; Optical properties; Photovoltaic cells; Quality control; Radiative recombination; Rapid thermal annealing; Recombination; Solar cells; Superlattices; Voltage; Molecular beam epitaxy; Rapid thermal annealing; GaAsSbN; Superlattices; Open circuit voltage; Multi-junction solar cells
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2019.109949

In this work we investigate the effect of rapid thermal annealing (RTA) on the performance of solar cells consisting of different GaAsSbN-based structures and correlate the device results with modifications of the optical and structural properties of the alloy. In particular, bulk layers grown at different growth rates and type-II GaAsSb/GaAsN superlattices with different period thickness are analyzed. We find evidences of material quality improvement after the annealing process such as a reduction of N-related radiative defects and Sb clusters. These RTA-induced changes lead to a notable enhancement of the open circuit voltage (VOC), which results in values of the bandgap-voltage offset (WOC = EG/q-VOC) comparable to that of a non-optimized reference GaAs solar cell with the same device structure (WOC ∼0.63 eV). The decrease in WOC after annealing shows a correlation with the reduced radiative recombination at low energy N-related sub-bandgap states. These results suggest that radiative recombination in a broad band of deep defect states is a source of VOC degradation in GaAsSbN solar cells.
•Sub-bandgap deep radiative states induced by N are present in GaAs(Sb)N.•Reduction of the N-related radiative defect density after rapid thermal annealing.•Elimination of sub-bandgap optically active states correlates with enhanced VOC.•WOC values of GaAsSbN solar cells comparable to reference GaAs cell (∼0.63 eV).