Adiabatic two-step photoexcitation effects in intermediate-band solar cells with quantum dot-in-well structure

Abstract

We studied the dynamics of electrons generated by two-step photoexcitation in an intermediate-band solar cell (IBSC) comprising InAs/GaAs/Al 0.3 Ga 0.7 As dot-in-well (DWELL) structure using time-resolved photocurrent (TRPC) measurement. The examined IBSC exhibited considerably slower photocurrent decay than a conventional InAs/GaAs quantum dot IBSC, which is due to the extraordinarily long-lived electrons in the DWELL. In order to retrieve the electron lifetime from the decay profile, we developed a model reproducing the observed decay and performed parameter fitting. The fitting results indicate that the electron lifetime in the DWELL is approximately 30 μs. In the two-colour excitation TRPC measurement, we found that an additional infrared (IR) light accelerates the photocurrent decay while the photocurrent increases by approximately 3%, because the additional IR light causes two-step photoexcitation of electrons in the DWELLs towards the conduction band. Furthermore, we demonstrated that the open-circuit voltage increases with increasing of the contribution of the second IR excitation process.

Reciprocal Relation Between Intraband Carrier Generation and Interband Recombination at the Heterointerface of Two-Step Photon Up-Conversion Solar Cells

“…It is noted that the nonradiative component is overestimated because we do not take into account the weak PL from the InAs wetting layer and the GaAs in our analysis. Within the accuracy of our assumptions, we find that 7% of the photogenerated carriers in the GaAs are collected via TPU in our device at −0.6 V. As J p is generated by adiabatic excitation in the TPU process, it is expected that the output voltage will be boosted [36]. Figure 5(c) compares the voltage increase V that is induced by the TPU process and the IR-induced J p as a function of the bias voltage.…”

Room Temperature Operation of a Quantum Ratchet Intermediate Band Solar Cell

“…While room temperature two-photon photocurrent (TPP) results have been reported previously, [4][5][6][7][18][19][20][21] they were measured with steady state illumination schemes whose validity has come into question due to the likelihood of thermal artefacts. [22] Here we developed a high-speed double-demodulation two-photon spectroscopy setup (see Experimental Section) to measure the TPP, and to verify that its dynamical characteristics evidenced an electronic and not a thermal origin.…”

“…[1,2] A third set of energy states is introduced between the valence band (VB) and conduction band (CB) often termed "Intermediate Band" (IB), so that electrons can be promoted from the VB to CB by the sequential two-photon absorption (STPA) of photons with energies below the bulk bandgap, in a way that generates additional photocurrent and increases the theoretical efficiency limit to 46.7% under one sun. [2] A number of physical implementations have been trialed, [3][4][5][6][7] however, the presence of the IB often leads to additional non-radiative recombination channels. [8][9][10][11][12] Vaquero-Stainer et al demonstrated the successful operation, albeit at low temperature, of a quantum ratchet IBSC (QR-IBSC) using a quantum well superlattice (QWSL).…”

Diffusion photocurrent influenced by intraband excitation in an intermediate band solar cell with type-I band alignment

“…13,14) By employing a more casual device design, we reported that IBSCs based on quantum dots-in-a-well (DWELL) structures can be also promising. [17][18][19][20][21] In our Al 0.3 Ga 0.7 As p-i-n single-junction SC containing GaAs/ InAs/GaAs DWELL layers, the two-step excitation process occurs via a quantum well (QW) interband transition and a following QD intraband transition. There is a ratchet-like band alignment that deeply confines the photoexcited electrons after the QW interband excitation because these electrons are expected to undergo a quick relaxation from the QW to the QD before a second photon is absorbed.…”