Novel multijunction solar cell design for low cost, high concentration systems

Abstract

In the quest to reduce the levelized cost of energy, recent concentrated photovoltaics innovations have striven to increase the solar cell conversion efficiency. Another approach aims at concentrating more light on the solar cell in order to reduce its share of the energy cost. We propose new cell structures that are tailored for high conversion efficiency at solar concentration exceeding 1000 suns, with a minimum amount of heat generated. These designs are composed of multiple junctions (3, 4, and 5) of materials lattice matched to gallium arsenide (GaAs) with bandgaps at or above that of GaAs. Simulations that include thermal effects and electrical resistance effects are used to predict the performances of the proposed designs under high concentrations. A relative cost analysis shows a reduction in electricity cost when using these designs compared with the state of the art triple-junction solar cell. Further cost reduction schemes using these proposed designs are discussed.

Vertical-tunnel-junction (VTJ) solar cell for ultra-high light concentrations (>2000 suns)

“…Seoane and A. J. García-Loureiro are with the with the Centro Singular de Investigación en Tecnoloxías da Información (CITIUS), University of Santiago de Compostela, 15782, Spain, (natalia.seoane@usc.es; antonio.garcia.loureiro@usc.es). resistance (Rs) seems to limit the peak of the η at Cratio ≈< 1000-2000 suns [9]. Indeed, to the date, the developing of concentrator HSCs with η peaking at Cratio > 1000 suns still remains pending [10].…”

Ultra‐efficient intrinsic‐vertical‐tunnel‐junction structures for next‐generation concentrator solar cells

“…In this sense, the peak of efficiency of standard MJ solar cells seems to be limited to concentrations factors below 1000 suns, no matter how the front-grid pattern is designed or how much the area of the cell is reduced. 4,20 Hence, they cannot fully exploit the theoretical increase of η with C ratio and therefore to completely leverage the cost reduction capacity of UHCPV systems. 21 Vertical-MJ (VMJ) solar cells are based on the series connection of multiple subcells with the metal contacts located on the lateral.…”

“…This limitation is imposed by the trade‐off between the shadowing of the front metallic contact and the R s, 5 as well as by the R s of the different semiconductor layers that compose the MJ device. In this sense, the peak of efficiency of standard MJ solar cells seems to be limited to concentrations factors below 1000 suns, no matter how the front‐grid pattern is designed or how much the area of the cell is reduced 4,20 . Hence, they cannot fully exploit the theoretical increase of η with C ratio and therefore to completely leverage the cost reduction capacity of UHCPV systems 21 …”

“…1 This can be understood considering that the theoretical efficiency (η) of a solar cell grows with concentration while reducing the amount of semiconductor material, which is the most expensive element of the system. 2 Despite the great potential of this technology, significant efforts are still needed to investigate the main technological challenges, namely, (a) solar cells with efficiencies peaking at UH levels, [3][4][5][6][7] (b) optical designs able to reach UH levels with an adequate optical performance [8][9][10][11] and (c) thermal studies tailored to understand the performance of the cells and/or to produce module configurations aimed to remove or exploit the UH heat waste. [12][13][14][15][16] This communication is focused on the first issue.…”

Challenges and strategies for implementing the vertical epitaxial heterostructure architechture (VEHSA) design for concentrated photovoltaic applications

“…We would like to bridge the gap between research in LPCs and CPVs by proposing that we apply the very technology that makes VEHSA devices so efficient to CPV cells themselves, namely, stacked thin junctions. The working principle here is that splitting the photocurrent over many junctions reduces I R 2 losses and loads on the tunnel junction, allowing for the possibility of operation under high solar concentration (with the goal being in excess of 1000 suns [45]). There is an added benefit of using a vertical arrangement of thin junctions since thin layers achieve a greater Fermi level splitting [46], which on a per-junction level offers a marginal boost in V oc when compared to a planar arrangement of bulk cells (potentially 92 mV per junction [38]).…”