Intraband absorption in finite, inhomogeneous quantum dot stacks for intermediate band solar cells: limitations and optimization

TL;DR

This paper theoretically analyzes intraband optical transitions in finite, inhomogeneous quantum dot stacks, revealing how inter-dot coupling influences absorption spectra and transition rates, with implications for optimizing intermediate band solar cells.

Contribution

It introduces a model for inhomogeneous quantum dot stacks, showing how inter-dot coupling affects absorption spectra and transition rates, and identifies factors critical for solar cell efficiency.

Findings

Absorption spectra develop multiple maxima with increasing dots.

Transition rate enhancement saturates after a few quantum dots.

Inter-dot coupling strength is crucial for stability against inhomogeneity.

Abstract

We present a theoretical analysis of intraband optical transitions from the intermediate pseudo-band of confined states to the conduction band in a finite, inhomogeneous stack of self-assembled semiconductor quantum dots. The chain is modeled with an effective Hamiltonian including nearest-neighbor tunnel couplings and the absorption under illumination with both coherent (laser) and thermal radiation is discussed. We show that the absorption spectrum already for a few coupled dots differs from that of a single dot and develops a structure with additional maxima at higher energies. We find out that this leads to an enhancement of the overall transition rate under solar illumination by up to several per cent which grows with the number of QDs but saturates already for a few QDs in the chain. The decisive role of the strength of inter-dot coupling for the stability of this enhancement against QD stack inhomogeneity and temperature is revealed.