Capping vertically aligned InGaAs/GaAs(Sb) quantum dots with a AlGaAsSb spacer layer in intermediate‐band solar cell devices

Abstract

This study demonstrated the feasibility of fabricating a highly stacked vertically aligned InGaAs/GaAs(Sb) quantum dot (QD) structure with an AlGaAsSb spacer layer for improving the device performance of QD intermediate-band solar cell (QD-IBSC) devices. The power-dependent photoluminescence measurements of the proposed structure revealed a blueshift in the QD ground-state emissions when the excitation power was increased, indicating the formation of an intermediate band inside the QD structure. Capping the InGaAs QDs with a GaAsSb layer prevented the QDs from collapsing because there was less In-Ga intermixing between the QDs and GaAsSb layer. In addition to maintaining the QD structure, the carrier lifetime was extended by tuning the energy band alignment of the InGaAs/GaAsSb QD structure. Inserting the AlGaAsSb layer into the spacer layer increased the band gap, which in turn increased the open-circuit voltage of the QD-IBSC. The QD-IBSC in this work shows an extension of external-quantum efficiency by up to 1200 nm (compared with a GaAs reference cell) through the absorption by QDs and increased the open-circuit voltage from 0.67 to 0.70 V by adopting the AlGaAsSb spacer layer. These results confirm that adopting a columnar InGaAs/GaAs(Sb) QD structure with a AlGaAsSb spacer layer can enhance the performance of QD-IBSC devices.

Performance optimization of In(Ga)As quantum dot intermediate band solar cells

“…Also, AlAs CL prevents in segregation and In-Ga intermixing, and reduces QDs decomposition [ 54 , 55 ]. In addition to AlAs, the CLs commonly used include InGaAs, InAlGaAs, AlGaAsSb and so on, and different CLs have different effects [ 56 – 58 ]. Wei-Sheng Liu et al fabricated an InGaAs/GaAs(Sb) QDs with AlGaAsSb CL.…”

“…Wei-Sheng Liu et al fabricated an InGaAs/GaAs(Sb) QDs with AlGaAsSb CL. It showed an enlarged band gap with the inserting of AlGaAsSb CL and the V oc is increased from 0.67 to 0.7 V [ 58 ]. T. Sugaya et al found that the In 0.2 Ga 0.8 As CLs on In 0.4 Ga 0.6 As QD solar cells could reduce the strain around the QDs and 50-stack InGaAs QDs can be grown without defects.…”

Tailoring Energy Band Alignment of Vertically Aligned InGaAs Quantum Dots Capped with GaAs(Sb)/AlGaAsSb Composite Structure after Thermal Annealing Treatment

“…Vertically aligned QD structures with reduced spacer layer thickness have been observed to present several challenges that need to be overcome, such as dot-size uniformity, the formation of nonradiative recombination centers resulting from the epitaxial defects, low V oc , and the low optoelectronic conversion efficiency of the InAs/GaAs QD-IBSCs. ,− Due to the reduced GaAs spacer layer thickness in a multistack InAs/GaAs QD structure for electronic state coupling, the increased structural compressive strain can generate crystal dislocations, reducing the carrier lifetime and worsening the device characteristics of the QD-IBSCs.…”

“…The increased density of dislocations in multistack QD structures can worsen the short-circuit current density and open-circuit voltage of the QD-IBSC . Therefore, the extended carrier lifetime in a QD array with reduced crystal defects is critical to enhance the absorption of sub-band-gap photons and the current–voltage characteristics in a QD-IBSC. ,, …”

“…7 Therefore, the extended carrier lifetime in a QD array with reduced crystal defects is critical to enhance the absorption of sub-band-gap photons and the current−voltage characteristics in a QD-IBSC. 7,9,10 Various overgrown strain-compensation layers or strainreduction layers have been used in InGaAs QD heterostructures to mitigate compressive strain and to modify energy band alignment, with the purpose of extending carrier lifetime. 11−13 QDs with strain-reducing layers have been observed to exhibit increased emission wavelengths because of the reduction of the hydrostatic compressive strain and strain-induced In−Ga intermixing inside the QDs.…”