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

Abstract

The efficiency of solar cells can be enhanced by increasing the light intensity and/or the number of bandgaps of the structure. However, current solar cells cannot fully exploit these two factors because of various critical drawbacks. Here, we show a novel microscale, that is, side ≈ 0.5 mm, vertical solar cell structure that does not suffer the series resistance and bandgap limitations issues of current devices. The preliminary structures investigated show extreme efficiencies, >40%, at ultrahigh concentration factors of 15 000 suns. In addition, future designs with a better bandgap configuration are expected to deliver cells with efficiencies far above 50% at extreme light intensities. This early design offers a fast and reliable route to push the efficiency towards the maximum solar conversion limit and represents a promising way to develop new‐generation ultraefficient and low‐cost concentrator photovoltaic systems.

Dependence of the vertical‐tunnel‐junction GaAs solar cell on concentration and temperature

“…Finally, Figure 8 (d) shows the efficiency (η) as a function of C ratio for all temperatures under consideration. As is evident, η tends to grow linearly with C ratio and is not limited by the R S losses, in contrast to the standard MJ concentrator cells, which present efficiencies peaking at concentrations of approximately 500 suns [22,58]. η varies from 30.88 to 32.30 % at 298 K, and from 23.80 to 25.75 % at 423 K. This can be explained by the following known expression: in combination with Equations ( 20) and (22), which leads to the following relationship:…”

“…Finally, Figure 8 (d) shows the efficiency ( η ) as a function of C ratio for all temperatures under consideration. As is evident, η tends to grow linearly with C ratio and is not limited by the R S losses, in contrast to the standard MJ concentrator cells, which present efficiencies peaking at concentrations of approximately 500 suns [22, 58]. η varies from 30.88 to 32.30 % at 298 K, and from 23.80 to 25.75 % at 423 K. This can be explained by the following known expression: $$\begin{equation} \eta = \frac{{{P_{\max }}}}{{{A_{{\rm{ill}}}}\cdot 1000\cdot{C_{{\rm{ratio}}}}}} = \frac{{{V_{{\rm{OC}}}}\cdot{I_{{\rm{SC}}}}\cdot FF}}{{{A_{{\rm{ill}}}}\cdot 1000\cdot{C_{{\rm{ratio}}}}}}\end{equation}$$…”

Laser Power Converter Architectures Based on 3C‐SiC with Efficiencies >80%

“…This architecture shows a drastic reduction of series resistance and the absence of shadowing due to the metal grid. [36][37][38] Another interesting feature is the possibility to connect several devices via tunnel junctions to increase the illumination area. [36] This could be achieved by monolithically growing multiple subcells on the top of each other, as in standard multijunction concentrator solar cells.…”

“…This work was carried out using Silvaco Atlas Software, [34] a TCAD simulator able to provide realistic and trustable results when modeling a wide variety of electronic devices, including photovoltaic solar cells. For instance, Michael et al [42] applied it in the design and optimization of a III-V multijunction, Ochoa et al [43] improved the efficiency of a multijunction concentrator under 5000 suns by optimizing the window layer and Seoane et al [38] studied a vertical tunnel junction under 15 000 suns. ATLAS was also applied to design and optimize vertical laser power converters by Outes et al, [22] and to evaluate the impact of design variables in a vertical epitaxial heterostructure architecture (VEHSA) LPC by York et al [44] In this work, Poisson and continuity equations were solved to obtain the main properties and characteristics of each device configuration.…”

“…[63] Note that in the vLPC architecture the junctions are parallel to the light flow, and several identical single units can be vertically stacked without changing their structure, in order to obtain the same current in each single unit, so without increasing the series resistance losses. [22,38] This simplifies the design and makes it robust against temperature variations (due to change in energy gap and photon absorption), compared to the VEHSA architecture. Finally, it is important to mention that the active area of both architectures can be further increased if needed by arranging the single units onto a series/parallel-connected module.…”