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Energies 2015, 8(6), 5440-5458; doi:10.3390/en8065440

Next Generation Solar Cells Based on Graded Bandgap Device Structures Utilising Rod-Type Nano-Materials

1
Materials and Engineering Research Institute, Sheffield Hallam University, Sheffield S1 1WB, UK
2
Conn Centre for Renewable Energy Research, University of Louiseville, Kentucky, KY 40292, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Andrés G. Muñoz
Received: 25 February 2015 / Revised: 6 May 2015 / Accepted: 11 May 2015 / Published: 5 June 2015
(This article belongs to the Special Issue Next Generation of Photovoltaic (PV) Technology)
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Abstract

Current solar cells under research and development utilise mainly one absorber layer limiting the photon harvesting capabilities. In order to develop next generation solar cells, research should move towards effective photon harvesting methods utilising low-cost solar energy materials. This will lead to reduce the $W−1 figure for direct solar energy conversion to electrical energy. In this work, a graded bandgap solar cell has been designed to absorb all photons from the UV, visible and IR regions. In addition, impurity PV effect and impact ionisation have been incorporated to enhance charge carrier creation within the same device. This new design has been experimentally tested using the most researched MOCVD grown GaAs/AlGaAs system, in order to confirm its validity. Devices with high Voc ~ 1175 mV and the highest possible FF ~ (0.85–0.87) have been produced, increasing the conversion efficiency to ~20% within only two growth runs. These devices were also experimentally tested for the existence of impurity PV effect and impact ionisation. The devices are PV active in complete darkness producing over 800 mV, Voc indicating the harvesting of IR radiation from the surroundings through impurity PV effect. The quantum efficiency measurements show over 140% signal confirming the contribution to PV action from impact ionisation. Since the concept is successfully proven, the low-cost and scalable electrodeposited semiconducting layers are used to produce graded bandgap solar cell structures. The utilisation of nano- and micro-rod type materials in graded bandgap devices are also presented and discussed in this paper. Preliminary work on glass/FTO/n-ZnS/n-CdS/n-CdTe/Au graded bandgap devices show 10%–12% efficient devices indicating extremely high Jsc values ~48 mA·cm−2, showing the high potential of these devices in achieving higher efficiencies. The detailed results on these low-cost and novel graded bandgap devices are presented in a separate publication. View Full-Text
Keywords: graded bandgap structures; next generation solar cells; impurity PV effect; impact ionisation; nano-materials graded bandgap structures; next generation solar cells; impurity PV effect; impact ionisation; nano-materials
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Dharmadasa, I.M.; Ojo, A.A.; Salim, H.I.; Dharmadasa, R. Next Generation Solar Cells Based on Graded Bandgap Device Structures Utilising Rod-Type Nano-Materials. Energies 2015, 8, 5440-5458.

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