Electrical and optical characterizations of InAs/GaAs quantum dot solar cells

The electrical and optical characterizations of InAs/GaAs quantum dot solar cells (QDSCs) were investigated by frequency dependent capacitance–voltage ( C – V ) measurements and photoreflectance (PR) spectroscopy. The C – V results confirmed that the frequency dependent junction capacitance ( C j ) of QDSC is sensitive to the carrier exhaustion process through trapping and recapturing in the strain-induced defects and QD states caused by the interface strain between InAs and GaAs materials. As a result, at a low frequency (≤ 200 kHz), the C j of the QDSCs decreased with increasing InAs deposition thickness ( θ ), leading to the decrease in carrier concentration ( N d ) of the n-GaAs absorber layer due to the carrier losses processes caused by the trapping and re-capturing in the defects and the relatively large QDs. At θ ≤ 2.0 ML, the p-n junction electric field strength ( F pn ) of the QDSCs which was evaluated by PR spectra decreased with increasing excitation photon intensity ( I ex ) due to the typical field screening effect in the SC structure. On the other hand, the F pn of QDSCs with θ ≥ 2.5 ML approached a constant value with a relatively high I ex , which suggests that the decrease in photo-generated carriers in the QDSC was caused by the re-capturing and trapping process.