Electrical and optical characterizations of InAs/GaAs quantum dot solar cells
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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 (Cj) 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 Cj of the QDSCs decreased with increasing InAs deposition thickness (θ), leading to the decrease in carrier concentration (Nd) 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 (Fpn) of the QDSCs which was evaluated by PR spectra decreased with increasing excitation photon intensity (Iex) due to the typical field screening effect in the SC structure. On the other hand, the Fpn of QDSCs with θ ≥ 2.5 ML approached a constant value with a relatively high Iex, which suggests that the decrease in photo-generated carriers in the QDSC was caused by the re-capturing and trapping process.
This study was partially supported by Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2014R1A6A1031189). This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No. 20163030013380).
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