Near 1 V open circuit voltage InAs/GaAs quantum dot solar cells

Bailey, Christopher G.; Forbes, David V.; Raffaelle, Ryne P.; Hubbard, Seth M.

doi:10.1063/1.3580765

Cited by 226 publications

(149 citation statements)

References 20 publications

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“…QDs of the desired size (down to 2-3 nm) have been produced through this technique 50 and can be implemented with several material options that give a bandgap distribution close to the optimum value of 1.95 eV, with good lattice matching. Nevertheless, some carefully manufactured InAs/GaAs cells have already presented minor voltage reductions 18,19 and are therefore probably already operating as IB cells at room temperature.…”

Section: Summary and Challengesmentioning

confidence: 99%

Understanding intermediate-band solar cells

2012

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The intermediate-band solar cell is designed to provide a large photogenerated current while maintaining a high output voltage. To make this possible, these cells incorporate an energy band that is partially filled with electrons within the forbidden bandgap of a semiconductor. Photons with insufficient energy to pump electrons from the valence band to the conduction band can use this intermediate band as a stepping stone to generate an electron-hole pair. Nanostructured materials and certain alloys have been employed in the practical implementation of intermediate-band solar cells, although challenges still remain for realizing practical devices. Here we offer our present understanding of intermediate-band solar cells, as well as a review of the different approaches pursed for their practical implementation. We also discuss how best to resolve the remaining technical issues.T he intermediate-band (IB) solar cell consists of an IB material sandwiched between two ordinary n-and p-type semiconductors 1 , which act as selective contacts to the conduction band (CB) and valence band (VB), respectively (Fig. la). In an IB material, sub-bandgap energy photons are absorbed through transitions from the VB to the IB and from the IB to the CB, which together add up to the current of conventional photons absorbed through the VB-CB transition. In 1997 2 , researchers used hypotheses similar to those adopted by Shockley and Queisser in 1961 3 to derive a detailed balance-limiting efficiency of 63% for the IB solar cell, at isotropic sunlight illumination (concentration of 46,050 suns) and assuming Sun and Earth temperatures to be 6,000 K and 300 K, respectively (Fig. lb). This work also presented the Shockley-Queisser limiting efficiency of 41% for single-gap solar cells operating under the same conditions 2 . The limiting efficiency of the IB solar cell is similar to that of a triple-junction solar cell connected in series. However, the IB can be regarded 4 as a set of two cells connected in series (corresponding to the VB-IB and IB-CB transitions) and one in parallel (corresponding to the VB-CB transition). This provides the IB solar cell with additional tolerance to changes in the solar spectrum.An optimal IB solar cellhas a total bandgap of about 1.95 eV, which is split by the IB into two sub-bandgaps of approximately 0.71 eV and 1.24 eV The quasi-Fermi levels (QFLs) or electrochemical potentials of the electrons in the different bands are usually close to the edges of the bands. Because the voltage of any solar cell is the difference between the CB QFL at the electrode in contact with the n-type side and the VB QFL at the electrode in contact with the p-type side, the maximum photovoltage of the IB solar cell is limited to 1.95 eV, although it is still capable of absorbing photons of energy above 0.71 eV In contrast, single-gap solar cells cannot supply a voltage greater than the lowest photon energy they can absorb. IB solar cells can deliver a high photovoltage by absorbing two subbandgap photons to produce one high ...

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Section: Summary and Challengesmentioning

confidence: 99%

Understanding intermediate-band solar cells

2012

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“…Many efforts are being made to avoid voltage degradation of the IBSCs and promising results have been obtained [10,11]. It has been demonstrated that, at RT, the thermal carrier escape from the IB to the CB dominates the extraction of photocurrent [12].…”

Section: Introductionmentioning

confidence: 99%

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

Ramiro

Antolín

Steer

et al. 2012

2012 38th IEEE Photovoltaic Specialists Conference

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-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.

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“…We believe this continuum tailing states superposed with QD and WL induced confined energy states within the forbidden band function as an efficient carrier relaxation and collection pathway [6][7][8] . A slight enhancement of Jsc, accompanied by a degradation of Voc [6][7][8][9][10][11][12] , under one sun illumination and room temperature conditions can be completely explained by a single-photon absorption process via below-bandgap states including both quantum confined states and tailing states. The degradation of Voc is related to an increased dark current resulting from a direct carrier collection/relaxation via the tailing states.…”

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confidence: 99%

Non-resonant below-bandgap two-photon absorption in quantum dot solar cells

Dagenais

2015

Applied Physics Letters

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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.

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Near 1 V open circuit voltage InAs/GaAs quantum dot solar cells

Cited by 226 publications

References 20 publications

Understanding intermediate-band solar cells

Understanding intermediate-band solar cells

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

Non-resonant below-bandgap two-photon absorption in quantum dot solar cells

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