Effect of internal electric field on InAs/GaAs quantum dot solar cells

Abstract

We studied time-resolved carrier recombination in InAs/GaAs quantum dot (QD) solar cells. The electric field in a p-i-n diode structure spatially separates photoexcited carriers in QDs, strongly affecting the conversion efficiency of intermediate-band solar cells. The radiative decay lifetime is dramatically reduced in a strong electric field (193 kV/cm) by efficient recombination due to strong carrier localization in each QD and significant tunneling-assisted electron escape. Conversely, an electric field of the order of 10 kV/cm maintains electronic coupling in the stacked QDs and diminishes tunneling-assisted electron escape.

Understanding the electric field control of the electronic and optical properties of strongly-coupled multi-layered quantum dot molecules

“…We consider electric fields both parallel to the growth direction [001] (labelled as E p ) and anti-parallel to the growth direction (labelled as E a ). The magnitude of the electric fields is varied between 0 and 45 KV/cm, which is in accordance with the range of the electric fields recently investigated in an experimental study for the design of solar cell devices [25]. The atomistic simulations are performed using nanoelectronic modeling tool NEMO-3D [42][43][44].…”

“…published experiments. The experimental studies [16,25] have not reported any In-Ga intermixing for the QDMs. Therefore we have ignored this effect in our simulations.…”

“…Intriguingly this raises a question that as the electric field pushes the electron wave functions towards the edges of the QDM thereby increasing their quantum confinement, does this weaken the interdot coupling, and at what field magnitude the interdot coupling completely breaks down? A recent experimental study [25] attempted to probe this question by measuring electric field dependent PL spectra. They suggested that an electrical field of 10 KV/cm maintains the strong interdot coupling of the QD layers, which completely break down at very large field magnitudes.…”

“…For many applications such as photodetectors, photovoltaics (such as IBSCs), and quantum information devices, the QDMs are also subject to electric fields, which can significantly influence their electronic structure. Such fields are either present internally such as investigated recently for the solar cells [25,26], or can be applied externally to purposely tune the properties of the devices for a certain operation [14]. Although the impact of electric fields has been extensively studied in the literature for the single QDs [27][28][29], the bi-layer QDMs [7,[30][31][32][33][34], and for the small QD stacks consisting of three to four QD layers [35], to-date no theoretical understanding is available on the electronic and optical properties of the multi-layer QDMs under the influence of electrical fields.…”

Recent progress on quantum dot solar cells: a review

“…The effect of the internal electric field on carrier escape and separation was investigated quantitatively by Kasamatsu et al 50 They have experimentally fabricated InAs/GaAs QDSC with different built-in electric fields by controlling the thickness of intrinsic buffer layers surrounding the InAs/GaAs QDs. The internal electric fields applied to the QDs were estimated as 46 and 193 kV∕cm when the total intrinsic layer thicknesses were 299.3 and 69.8 nm, respectively.…”