Non-Resonant Below-Bandgap Two-Photon Absorption in Quantum Dot Solar Cells

TL;DR

This study demonstrates that sub-bandgap photons can significantly generate photocurrent in quantum dot solar cells through both one- and two-photon absorption processes, with clear experimental evidence and quantification.

Contribution

First experimental demonstration of sub-bandgap photon contribution to photocurrent via 1PA and 2PA in quantum dot solar cells, highlighting the role of tailing states.

Findings

Photons below the quantum dot transition energy can generate photocurrent.

Both 1PA and 2PA processes contribute to photocurrent at 1550 nm.

Quantitative evaluation of absorption efficiencies in InAs/GaAs QD devices.

Abstract

We are the first to show with clear experimental results that photons that have energy lower than the transition energy between quantum dots states and valance band can still contribute greatly to the photocurrent via both one-photon absorption process (1PA) and two-photon absorption process (2PA). The tailing states function as both the energy states for low energy photon absorption and the photocarriers extraction pathway. One of the biggest advantages of our method is that it can clearly differentiate the photocurrent due to 1PA process and 2PA process. Both 1PA and 2PA photocurrent generation efficiency in an InAs/GaAs QD device with photon excitation at 1550 nm have been quantitatively evaluated.