Fabrication and characterization of InAs/InGaAs sub-monolayer quantum dot solar cell with dot-in-a-well structure

To improve the efficiency of InAs quantum dot solar cells (QDSCs), we propose a QDSC structure with sub-monolayer (SML) QDs. The optical and electrical properties of Stranski-Krastanow (SK) QDs and SML-QDs embedded in dot-in-a-well (DWELL) were investigated by photoluminescence and photoreflectance spectroscopy and illuminated J-V measurement. The SML-QDSC showed the improved probability of carriers thermally escaping from the QD states due to the small QD size. The suppression of carrier re-capturing enhanced the photovoltaic effect due to the enhanced carrier screening. The conversion efficiency of the SML-QDSC (η = 10.65%) was enhanced by about 12.58% compared to that of the SK-QDSC (η = 9.46%). The improved SC efficiency of the SML-QD is attributed to the suppressed carrier re-capturing and carrier trapping caused by the smaller QD size and lower defect density.