Emission Spectroscopy Investigation of the Enhancement of Carrier Collection Efficiency in AgBiS2-Nanocrystal/ZnO-Nanowire Heterojunction Solar Cells

Eco-friendly solar cells were fabricated using interdigitated layers comprising ZnO nanowires (NWs) and infrared absorbing AgBiS2 nanocrystals (ITO/ZnO NWs/AgBiS2/P3HT/Au). The quality of ZnO NWs was studied using photoluminescence and Raman spectroscopy to identify the defects in ZnO NWs influencing solar cell performance. Oxygen vacancies and Zn interstitial sites, among various recombination sites, were observed to be the main sites for carrier recombination, which hinders the carrier collection in the solar cells. Accordingly, the power conversion efficiency of AgBiS2 solar cells exhibited a good correlation with the number of oxygen vacancies. The structural order and electron-phonon interaction in ZnO NWs were also investigated via Raman scattering spectroscopy. A lower concentration of oxygen vacancies and zinc interstitials (Zni) resulted in a higher structural order as well as a weaker electron-phonon interaction in ZnO NWs. When ZnO NWs were treated at 500 degrees C in oxygen with the lowest oxygen vacancy concentration, the solar cells (500-O-2 solar cell (SC)) demonstrated an external quantum efficiency of approximately 70% in the visible region and a corresponding internal quantum efficiency of more than 80%. The 500-O-2 SC exhibited a power conversion efficiency of 5.41% (JSC = 22.21 mA/cm(2), VOC = 0.41 V, and FF = 60%) under quasi one-sun illumination. New methods that can efficiently reduce oxygen vacancies and Zni without affecting the structural order of ZnO NWs would further enhance the carrier collection efficiency. Moreover, since ZnO is a key electron transport material for constructing not only colloidal quantum dot solar cells but also other emerging solar cells, such as organic thin-film solar cells, the present findings provide significant information for improving their performance.

Automated summary

This study fabricated eco-friendly solar cells using interdigitated layers consisting of ZnO nanowires and infrared absorbing AgBiS2 nanocrystals. The quality of ZnO nanowires and its defects affecting solar cell performance were investigated. Oxygen vacancies and Zn interstitial sites were identified as the main recombination sites, hindering carrier collection in the solar cells. By reducing the concentration of these defects, the structural order and electron-phonon interaction in ZnO nanowires were improved. Furthermore, the study emphasized the significance of reducing defects in ZnO for improving not only colloidal quantum dot solar cells but also other emerging solar cell technologies.