Silicon is the predominant semiconductor in photovoltaics. However, the conversion efficiency of silicon single junction solar cells is intrinsically constrained to 29.4%, and practically limited around 27%. It is nonetheless possible to overcome this limit by combining silicon with high bandgap materials, such as III-V semiconductors, in a multi-junction device. Despite numerous studies tackling III-V/Si integration, the significant challenges associated with this material combination has hindered the development of highly efficient III-V/Si solar cells. Here we demonstrate for the first time a III-V/Si cell reaching similar performances than standard III-V/Ge triple-junctions solar cells. This device is fabricated using wafer bonding to permanently join a GaInP/GaAs top cell with a silicon bottom cell.The key issues of III-V/Si interface recombination and silicon weak absorption are addressed using polysilicon/SiOx passivating contacts and a novel rear side diffraction grating for the silicon bottom cell. With these combined features, we demonstrate a 2-terminal GaInP/GaAs//Si solar cell reaching a 1sun AM1.5g conversion efficiency of 33.3%.

A high-pressure dc glow discharge based on micro-structured-electrode (MSE) arrays was investigated by diode laser atomic absorption spectroscopy. The microdischarge was studied at constant current in pure Ar for pressures ranging from 50 to 400 mbar. The measurements of the absolute population density of the excited 1s 5 , 1s 4 , 1s 3 , and 1s 2 levels of Ar in the discharge revealed a population density of excited atoms in metastable and resonance states in the range 10 12-10 15 cm −3. The gas temperature and the electron number density were evaluated from the analysis of the absorption line profiles, taking into account significant broadening mechanisms. The gas temperature, derived from the Doppler broadening, was found to increase with pressure from 380 K at 50 mbar to 1100 K at 400 mbar. The electron number density was calculated from the Stark broadening and shift, and it ranges from 9 × 10 14 to 5 × 10 15 cm −3. The MSE-sustained discharges are combining the non-equilibrium character with the advantage of high-pressure, which recommends them for non-thermal plasma processing e.g. surface treatment, plasma chemistry and generation of UV and VUV radiation.

Conventional photovoltaic devices are currently made of relatively thick semiconductor layers, about 150 µm for silicon, and 2-4 µm for CIGS, CdTe or III-V direct bandgap semiconductors. Ultrathin solar cells using 10 times thinner absorbers could lead to considerable material and processing time savings. Theoretical models suggest that light trapping can compensate for the reduced single-pass absorption, but optical and electrical losses have greatly limited the performances of previous attempts. Here, we propose a strategy based on multiresonant absorption in planar active layers, and we report a 205 nm-thick GaAs solar cell with a certified 19.9% efficiency. It uses a nanostructured silver back mirror fabricated by soft nanoimprint lithography. Broadband light trapping is achieved with multiple overlapping resonances induced by the grating and identified as Fabry-Perot and guided-mode resonances. A comprehensive optical and electrical analysis of the complete solar cell architecture provides the pathway for further improvements and shows that 25% efficiency is a realistic shortterm target.

III–V//Si multijunction solar cells offer a pathway to increase the power conversion efficiency beyond the fundamental Auger limit of silicon single‐junctions. In this work, we demonstrate how the efficiency of a two‐terminal wafer‐bonded III–V//Si triple‐junction solar cell is increased from 34.1 % to 35.9 % under an AM1.5g spectrum, by optimising the III–V top structure. This is the highest reported efficiency to date for silicon‐based multijunction solar cell technologies. This improvement was accomplished by two main factors. First, the integration of a GaInAsP absorber in the middle cell increased the open‐circuit voltage by 51 mV. Second, a better current matching of all subcells enhanced the short‐circuit current by 0.7 mA/cm2. Two different growth directions, upright and inverted, were investigated. The highest cell efficiency of 35.9 % (Voc = 3.248 V, jsc = 13.1 mA/cm2, FF = 84.3 %) was achieved with an upright grown structure. Processing of upright structures requires additional bonding steps, which results in a reduced homogeneity of cell performance across the wafer. A detailed comparison with the currently best triple‐junction solar cell reveals future improvement opportunities and limits, considering voltage and current, respectively.

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The development of photovoltaics as a serious means of producing renewable energy has accelerated greatly in the last ten years, with prices for silicon-based solar cell systems dropping dramatically in the last few years. The next great opportunity for photovoltaics following this competitiveness in prices will be to enhance the cell and panel efficiencies. It is quite generally seen that the most viable platform on which this should be realized will be as augmented silicon solar cells, in which a top cell will be combined with the silicon bottom cell in a tandem configuration, by which the efficiency can be enhanced by a factor from 20% to 50%, depending on details of the approach. In this paper, we report on the status of one such approach, namely, with a top cell comprising III-V nanowires, connected to the bottom silicon cell in a two-terminal or four-terminal configuration. Among the most important opportunities, we show that a substrate-free growth, called Aerotaxy, offers a radical reduction in the total price picture. Besides the description of the key technical approaches, we also discuss the environmental issues.

A power-dependent relative photoluminescence measurement method is developed for double-heterostructures composed of III-V semiconductors. Analyzing the data yields insight into the radiative efficiency of the absorbing layer as a function of laser intensity. Four GaAs samples of different thicknesses are characterized, and the measured data are corrected for dependencies of carrier concentration and photon recycling. This correction procedure is described and discussed in detail in order to determine the material's Shockley-Read-Hall lifetime as a function of excitation intensity. The procedure assumes 100% internal radiative efficiency under the highest injection conditions, and we show this leads to less than 0.5% uncertainty. The resulting GaAs material demonstrates a 5.7 ± 0.5 ns nonradiative lifetime across all samples of similar doping (2–3 × 1017 cm−3) for an injected excess carrier concentration below 4 × 1012 cm−3. This increases considerably up to longer than 1 μs under high injection levels due to a trap saturation effect. The method is also shown to give insight into bulk and interface recombination.

In this paper we introduce the three-dimensional formulation of the OPTOS formalism, a matrix-based method that allows for the efficient simulation of non-coherent light propagation and absorption in thick textured sheets. As application examples, we calculate the absorptance of solar cells featuring textures on front and rear side with different feature sizes operating in different optical regimes. A discretization of polar and azimuth angle enables a three-dimensional description of systems with arbitrary surface textures. We present redistribution matrices for 3D surface textures, including pyramidal textures, binary crossed gratings and a Lambertian scatterer. The results of the OPTOS simulations for silicon sheets with different combinations of these surfaces are in accordance with both optical measurements and results based on established simulation methods like ray tracing. Using OPTOS, we show that the integration of a diffractive grating at the rear side of a silicon solar cell featuring a pyramidal front side results in absorption close to the Yablonovitch Limit enhancing the photocurrent density by 0.6 mA/cm² for a 200 µm thick cell.