Photocurrent spectroscopy of InAs/GaAs self-assembled quantum dots

Martı́

Antolín

et al. 2014

IEEE J. Photovoltaics

Abstract-The intermediate band solar cell (IBSC) has drawn the attention of the scientific community as a means to achieve high-efficiency solar cells. Complete IBSC devices have been manufactured using quantum dots, highly mismatched alloys, or bulk materials with deep-level impurities. Characterization of these devices has led, among other experimental results, to the demonstration of the two operating principles of an IBSC: the production of the photocurrent from the absorption of two below bandgap energy photons and the preservation of the output voltage of the solar cell. This study offers a thorough compilation of the most relevant reported results for the variety of technologies investigated and provides the reader with an updated record of IBSC experimental achievements. A table condensing the reported experimental results is presented, which provides information at a glance about achievements, as well as pending results, for every studied technology.

Section: ) Subbandgap Spectral Response or Quantum Efficiencymentioning

confidence: 99%

Review of Experimental Results Related to the Operation of Intermediate Band Solar Cells

Martı́

Antolín

et al. 2014

IEEE J. Photovoltaics

“…Thermal carrier escape is proportional to exp (-E A /kT), where k is the Boltzmann constant, T the temperature in Kelvin and E A is the activation energy of this process. The highest activation energies found in the literature for the InAs/GaAs system vary between 94 and 115 eV [12][13][14]. In [12] an activation energy of 224 meV was measured for sample SB, in which dots were capped with a specifically designed InAlGaAs QD capping layer [15].…”

Section: Introductionmentioning

confidence: 99%

InAs/AlGaAs quantum dot intermediate band solar cells with enlarged sub-bandgaps

2012 38th IEEE Photovoltaic Specialists Conference

Antolín

Steer

et al. 2012

-In the last decade several prototypes of intermediate band solar cells (IBSCs) have been manufactured. So far, most of these prototypes have been based on InAs/GaAs quantum dots (QDs) in order to implement the IB material. The key operation principles of the IB theory are two photon subbandgap (SBG) photocurrent, and output voltage preservation, and both have been experimentally demonstrated at low temperature. At room temperature (RT), however, thermal escape/relaxation between the conduction band (CB) and the IB prevents voltage preservation. To improve this situation, we have produced and characterized the first reported InAs/AlGaAs QDbased IBSCs. For an Al content of 25% in the host material, we have measured an activation energy of 361 meV for the thermal carrier escape. This energy is about 250 meV higher than the energies found in the literature for InAs/GaAs QD, and almost 140 meV higher than the activation energy obtained in our previous InAs/GaAs QD-IBSC prototypes including a specifically designed QD capping layer. This high value is responsible for the suppression of the SBG quantum efficiency under monochromatic illumination at around 220 K. We suggest that, if the energy split between the CB and the IB is large enough, activation energies as high as to suppress thermal carrier escape at room temperature (RT) can be achieved. In this respect, the InAs/AlGaAs system offers new possibilities to overcome some of the problems encountered in InAs/GaAs and opens the path for QD-IBSC devices capable of achieving high efficiency at RT.

“…This is because carrier thermal escape is inhibited as the temperature lowers, and tunnel escape is weak thanks to the thick spacers [7]. From the temperature dependency of the QE at the energy of the GSs transition, the activation energy of the carrier thermal escape can be measured [24]. This thermal process allows the detection of the sub-bandgap photocurrent in the QE measurement.…”

Section: B Resultsmentioning

confidence: 99%

Wide-Bandgap InAs/InGaP Quantum-Dot Intermediate Band Solar Cells

Villa

Lam

et al. 2015

IEEE J. Photovoltaics

Abstract-Current prototypes of quantum-dot intermediate band solar cells suffer from voltage reduction due to the existence of carrier thermal escape. An enlarged sub-bandgap E L would not only minimize this problem, but would also lead to a bandgap distribution that exploits more efficiently the solar spectrum. In this work we demonstrate InAs/InGaP QD-IBSC prototypes with the following bandgap distribution: E G = 1.88 eV, E H = 1.26 eV and E L > 0.4 eV. We have measured, for the first time in this material, both the interband and intraband transitions by means of photocurrent experiments. The activation energy of the carrier thermal escape in our devices has also been measured. It is found that its value, compared to InAs/GaAs-based prototypes, does not follow the increase in E L . The benefits of using thin AlGaAs barriers before and after the quantum-dot layers are analyzed.