Microscopic photoluminescence and photocurrent imaging spectroscopy of InAs nanostructures: Identification of photocarrier generation sites for intermediate-band solar cells

Abstract

We performed microscopic imaging of photoluminescence (PL) and photocurrent (PC) on InAs nanostructures including disklike structures (nanodisks) and quantum dots (QDs). The correlation between PL and PC images indicates that the major fraction of upconverted carriers originates from nanodisks. By analyzing the excitation spectra, we find evidence that nanodisks and QDs need to be spatially separated to enhance PC generation via upconversion. The efficient simultaneous use of both QDs and nanodisks is an alternative approach to intermediate-band solar cells, where low-energy photons are upconverted in the QDs and high-energy photons are efficiently upconverted in the nanodisks, resulting in enhanced carrier generation yields. With spatially resolved upconverted PL, we show that PC generation in nanodisks is due to ejection of both electrons and holes.