Development of lightweight space solar cells with 30% efficiency at end-of-life

The effects of electron irradiation on the performance of GaAs solar cells with a range of architectures is studied. Solar cells with shallow and deep junction designs processed on the native wafer as well as into a thin‐film were irradiated by 1‐MeV electrons with fluence up to 1×1015 e−/cm2. The degradation of the cell performance due to irradiation was studied experimentally and theoretically using model simulations, and a coherent set of minority carriers' lifetime damage constants was derived. The solar cell performance degradation primarily depends on the junction depth and the thickness of the active layers, whereas the material damage shows to be insensitive to the cell architecture and fabrication steps. The modeling study has pointed out that besides the reduction of carriers lifetime, the electron irradiation strongly affects the quality of hetero‐interfaces, an effect scarcely addressed in the literature. It is demonstrated that linear increase with the electron fluence of the surface recombination velocity at the front and rear hetero‐interfaces of the solar cell accurately describes the degradation of the spectral response and of the dark current characteristic upon irradiation. A shallow junction solar cell processed into a thin‐film device has the lowest sensitivity to electron radiation, showing an efficiency at the end of life equivalent to 82% of the beginning‐of‐life efficiency.

Section: Introductionmentioning

confidence: 99%

Electron radiation–induced degradation of GaAs solar cells with different architectures

Gruginskie

Cappelluti

Bauhuis

et al. 2020

“…Here, we report on the degradation of the performance at 1 sun of the Ge subcell due to the thermal load suffered in a 3JSC. Although this work is only focused on the GaInP/Ga(In)As/Ge 3JSC, the degradation observed and its mechanisms may also apply to other MJSC configurations such as upright metamorphic MJSCs or other MJSCs with 4 or 5 junctions grown on Ge …”

Section: Introductionmentioning

confidence: 99%

Degradation of Ge subcells by thermal load during the growth of multijunction solar cells

Barrigón

Ochoa

García

et al. 2017

Germanium solar cells are used as bottom subcells in many multijunction solar cell designs. The question remains whether the thermal load originated by the growth of the upper layers of the multijunction solar cell structure affects the Ge subcell performance. Here, we report and analyze the performance degradation of the Ge subcell due to such thermal load in lattice‐matched GaInP/Ga(In)As/Ge triple‐junction solar cells. Specifically, we have detected a quantum efficiency loss in the wavelength region corresponding to the emitter layer (which accounts for up to 20% loss in equivalent JSC) and up to 55 mV loss in VOC of the Ge subcell as compared with analogous devices grown as single‐junction Ge solar cells on the same type of substrates. We prove experimentally that there is no direct correlation between the loss in VOC and the doping level of the base. Our simulations show that both the JSC and VOC losses are consistent with a degradation of the minority carrier properties at the emitter, in particular at the initial nanometers of the emitter next to the emitter/window heterointerface. In addition, we also rule out the gradual emitter profile shape as the origin of the degradation observed. Our findings underscore the potential to obtain higher efficiencies in Ge‐based multijunction solar cells if strategies to mitigate the impact of the thermal load are taken into consideration.

“…Owing to intensive research efforts, III–V compound triple‐junction (3J) solar cells have achieved conversion efficiencies ( η sc ) that cannot be realized by single‐junction solar cell designs . However, further improvements in η sc are required to obtain higher specific powers (power‐to‐weight ratio).…”

Section: Introductionmentioning

confidence: 99%

“…Owing to intensive research efforts, III-V compound triple-junction (3J) solar cells have achieved conversion efficiencies (η sc ) that cannot be realized by single-junction solar cell designs. [1][2][3][4][5] However, further improvements in η sc are required to obtain higher specific powers (power-to-weight ratio). Considering the conventional multi-junction (MJ) solar cell design, two approaches are available to achieve a higher η sc .…”

Section: Introductionmentioning

confidence: 99%

Practical target values of Shockley–Read–Hall recombination rates in state‐of‐the‐art triple‐junction solar cells for realizing conversion efficiencies within 1% of the internal radiative limit

Nakamura

Imaizumi

Akiyama

et al. 2020

In order to identify the cause of the difference between actual efficiency and the theoretical limit in state‐of‐the‐art triple‐junction solar cells, we investigate the internal luminescence efficiency in the depletion region ( ηintdep). The average internal luminescence efficiency of the whole subcell volume ( trueηitalicint¯) is obtained experimentally, and the ηintdep is deduced by numerical calculations using rate equations. We find that trueηitalicint¯ and ηintdep agree well in the low‐recombination current regime including the maximum power point. This indicates that the non‐radiative recombination loss at the maximum power point strongly depends on the recombination in the depletion region. Furthermore, we determine the actual Shockley–Read–Hall recombination coefficient in the depletion region, Adep, which is proportional to the effective density of recombination centers. Our analysis reveals the target values of Adep required for realizing conversion efficiencies that are within 1% of the internal radiative limit. The analysis also clarifies the extent of reduction of the effective density of recombination centers (in the depletion region) that is required to realize a given target efficiency.