Selective etching of laser-modified silicon (Si) enables 3D micro-sculpturing, offering new opportunities for photovoltaic (PV) applications. This technique facilitates high-aspect-ratio microstructures for light trapping in solar cells, photon management in photodetectors, and MEMS fabrication. We optimize selective wet-chemical etching of crystalline silicon (c-Si) modified by an infrared (IR) nanosecond (ns) laser, achieving high selectivity and controlled etching rates [1]. Additionally, we ensure complete removal of defected regions, producing a smooth, damage-free surface, crucial for PV applications requiring long carrier lifetimes.

Upgraded metallurgical-grade silicon (UMG-Si) has the potential to reduce the cost of photovoltaic (PV) technology and improve its environmental profile. In this contribution, we summarize the extensive work made in the research and development of UMG technology for PV, which has led to the demonstration of UMG-Si as a competitive alternative to polysilicon for the production of high-efficiency multicrystalline solar cells and modules. The tailoring of the processing steps along the complete Ferrosolar’s UMG-Si manufacturing value chain is addressed, commencing with the purification stage that results in a moderately compensated material due to the presence of phosphorous and boron. Gallium is added as a dopant at the crystallization stage to obtain a uniform resistivity profile of ∼1 Ω cm along the ingot height. Defect engineering techniques based on phosphorus diffusion gettering are optimized to improve the bulk electronic quality of UMG-Si wafers. Black silicon texturing, compatible with subsequent gettering and surface passivation, is successfully implemented. Industrial-type aluminum back surface field (Al-BSF) and passivated emitter and rear cell (PERC) solar cells are fabricated, achieving cell efficiencies in the range of those obtained with conventional polysilicon substrates. TOPCon solar cell processing key steps are also tested to further evaluate the potential of the material in advanced device architectures beyond the PERC. Degradation mechanisms related to light exposure and operation temperature are shown to be insignificant in UMG PERC solar cells when a regeneration step is implemented, and PV modules with several years of outdoor operation demonstrated similar performance to reference ones based on poly-Si. Life cycle analysis (LCA) is carried out to evaluate the environmental impact of UMG-based PV technology when compared to poly-Si-based technology, considering different scenarios for both the manufacturing sites and the PV installations.

Improving the efficiency of silicon-based solar cells is imperative to maximise harnessing of solar power. The current improvements in efficiency were attained by better manufacturing techniques and purer materials. There is however indirect evidence that the so-called agglomerated grown-in defects in silicon have a direct impact on cell efficiency and if this is the case, the efficiency could be improved by crystal engineering. This study focuses on understanding the defect generation and growth mechanisms in commercial silicon crystals and their impact on cell efficiency. Silicon wafers from different parts of the crystal having a range of oxygen and dopant concentrations and growth profiles, were investigated. These crystals were characterized using various tools and techniques such as Infrared Light Scattering Tomography (LST) to measure the defect density, and Fourier Transform Infrared Spectroscopy (FTIR) to measure the oxygen concentration. Solar cells were then fabricated out of these wafers to measure the performance of the devices. An understanding of why and how such defects impact the yield of different silicon wafers will lead to a thorough understanding of the relationship between the defect types, size and densities and cell efficiency. Moreover, this study will also shed light on the development of crystal recipes or after-crystal procedures to eliminate or minimize these effects on solar cell performance.

Wide bandgap perovskites are being widely studied in view of their potential applications in tandem devices and other semitransparent photovoltaics. Vacuum deposition of perovskite thin films is advantageous as it allows the fabrication of multilayer devices, fine control over thickness and purity, and it can be upscaled to meet production needs. However, the vacuum processing of multicomponent perovskites (typically used to achieve wide bandgaps) is not straightforward, because one needs to simultaneously control several thermal sources during the deposition. Here a simplified dual‐source vacuum deposition method to obtain wide bandgap perovskite films is shown. The solar cells obtained with these materials have similar or even larger efficiency as those including multiple A‐cations, but are much more thermally stable, up to 3500 h at 85 °C for a perovskite with a bandgap of 1.64 eV. With optimized thickness, record efficiency of >19% and semitransparent devices with stabilized power output in excess of 17% are achieved.

High-quality multicrystalline Upgraded Metallurgical Grade Silicon (UMG-Si) offers significant advantages over conventional polysilicon-based PV technology, associated to lower cost, lower energy budget and lower carbon footprint. The aim of this study is twofold: on the one hand, to ascertain the efficiency potential of solar cells based on this material in terms of carrier lifetime; and on the other hand, to explore, as a result of that, the adoption of high-efficiency cell architectures by establishing an effective rear-side passivation scheme for the implementation of passivated emitter rear contact (PERC) devices. The carrier lifetime and the surface passivation efficacy are investigated for different passivating layer configurations after single and double P-diffusion gettering processes. Layer stacks consisting of Al2O3, SiOxNy and a-SiNx:H capping overlayers have been optimized, on industrial size, saw-damage-etched UMG wafers and results compared to those obtained using reference iodine-ethanol (IE) passivation. Diagnosis based on minority carrier lifetime and implied Voc (iVoc) measurements helped monitor the impact of parameter optimization on wafer quality, particularly after firing processes. Carrier lifetimes over 600 us at 10^15 cm-3 injection level as well as up to 790 us locally have been measured in UMG-Si wafers passivated with IE after a Phosphorus Diffusion Gettering (PDG), demonstrating the suitability of the material for high-efficiency cell architectures. Values higher than 300 us have been obtained with Al2O3-based passivation layers for gettered UMG wafers, with implied Voc values up to 710 mV. These record-breaking lifetimes and iVoc figures obtained with p-type multicrystalline UMG-Si material demonstrate a significant upgrading of its electronic quality by means of industry-scalable technical processes.

In this paper, we report on the influence of SiNx:H stoichiometry on Al2O3/SiNx:H passivation stacks. We analyze the fabricated dielectric layers with four methods: FTIR, C-V, PCD and EQE. SiNx:H with a lower refractive index (SiN1) is poorer in H content than the one with a higher refractive index (SiN2) according to FTIR peaks. The calculated fixed charge density of the non-fired SiN1 layer is larger than SiN2; however, Al2O3 layer has the greatest magnitude but in negative polarity. The charge density of the Al2O3/SiN1 stack increases in magnitude with an increase in peak firing temperature while the Al2O3/SiN2 stack shows a decrease in magnitude. Al2O3/SiN1 stack resists a higher peak temperature during the fast-firing process with a relatively small reduction in iV(oc) values on symmetrically etched p-Si wafers due to the relatively lower H content of SiN1. Our results suggest that the chemical passivation of Si is more pronounced than the field effect passivation. We also investigate the effect of SiNx:H on the PERC solar cells with Al2O3/SiN1 and Al2O3/SiN2 stacks. The EQE results measured on the fabricated PERC cells demonstrate that the IR response is better for the PERC solar cells with Al2O3/SiN1 rear stack passivation implying enhanced passivation.

Ion implanted PERC cells have already achieved power conversion efficiencies of about 20.0%. The process flows reported in the literature for the ion implanted PERC cells with commonly utilized Al2O3/SiNx rear passivation stack, which has the benefit of being less sensitive to surface roughness than SiO2/SiNx stack passivation, notably suffer from the additional process steps such as single side polishing and single side protection. Here, we present a simplified process flow for the fabrication of ion implanted PERC cells having Al2O3/SiNx stack passivation at the textured rear surface without any rear side processing, leading to a power conversion efficiency of 20% at large area. In this context, we show the sensitivity of solar cell efficiency to firing peak temperature, implantation dose, and Al2O3 thickness. The results of the present research will provide a basis for high efficiency implanted PERC cells with significantly reduced workload and cost.

The passivated emitter and rear cell (PERC) is an advantageous type of solar cell to reduce rear surface recombination [1] along with its improved back surface reflectivity [2]. Therefore, many research and developments have been taking place on this type of solar cell to increase the overall solar cell performance. In this study, different type of rear local contact opening patterns (line and dash) formed by industrial-type picosecond laser which has 532 nm wavelength with fixed laser contact opening (LCO) width on M2 p-type mono commercial blue wafers. Manufactured cells are investigated in terms of photovoltaic parameters depending on the rear metal fractions. We ablate rear dielectric passivation layer with 4 different LCO patterns by varying rear local contact pitches from 900 μm to 1200 μm by an increment of 100 μm using (1:1) dash pattern. Line pattern is used as reference pattern, which has 1500 μm line pitch and same contact width. Laser opening areas are analyzed by photoluminescence (PL) images as well as implied open circuit voltage (iVoc) measurements. Local contacts and formation of back surface field (BSF) has been analyzed by using scanning electron microscopy (SEM) for all types of LCOs after screen printing of aluminum paste. As a result, rear contact pattern with 3.19% metal fraction (1000 μm pitch) is found to be relatively more efficient than the others investigated in this study. When compared to reference line pattern, the optimized LCO pattern provides a gain in conversion efficiency of 0.35%, Voc of 6 mV and FF of 0.35 % on average.

We report on the direct growth and characterization of type-II InAs/GaSb superlattice (T2SL) MWIR photodetector structure grown on a GaAs substrate by molecular beam epitaxy. The designed photodetector structure contains 140 period of 8.0 ML InAs/8.3 ML GaSb p-i-n SL structure with a 50% cutoff wavelength of 3.78 pm. We achieved a peak specific detectivity (D*) and differential resistance area product at zero bias (R(0)A) of 1.3 x 10(12)cm Hz(1/2) W-1 and 10(4) Omega cm(2) at 80 K, respectively. The obtained D* value is the best value reported up to now for a T2SL MWIR p-i-n photodetector grown on a GaAs substrate. The crystalline quality and the uniformity of the grown structure were verified by high resolution X-ray diffraction method by measuring three different spots on grown structure on a full 4 inch SI GaAs substrate.

We report on the growth and opto-electronic characterization of type-II InAs/GaSb superlattice (SL) mid-wavelength infrared pin photodetector grown on a GaAs substrate. AlSb interfacial misfit array was employed at the GaAs buffer/GaSb epilayer interface to reduce the dislocation density of the SL structure grown on the lattice mismatched GaAs substrate. Optical and electrical performance of this sample (SL-GaAs) were then compared with the reference sample of the same structure grown on a GaSb substrate (SL-GaSb). At 80 K, the dark current density and the detectivity values of the pin photodetectors were recorded as 5.40. x. 10-3 A cm-2 and 2.34. x. 1010 cm Hz0.5W(-1) for the SL-GaAs and 9.50. x. 10(-4) A cm(-2) and 4.70. x. 1010 cm Hz0.5W(-1) for the SL-GaSb, respectively.

We report on the opto-electronic characterization of an InAs/GaSb superlattice (SL) midwave infrared p–i–n photodetector structure (pin-SL) in comparison with the same structure with no intentional doping (i-SL). Both structures were grown on an n-GaSb substrate using molecular beam epitaxy. The nominally undoped structure (i-SL) presented p–i–n like behavior and showed a photovoltaic mode photoresponse due to the residual doping and native defects in this material system. For ∼77 K operation, 0.76 and 0.11 A W–1 responsivity values were obtained at 4 μm from the pin-SL and i-SL structures, respectively. Activation energy analysis showed that the recombination current was dominant in both structures but different recombination centers were involved. The same i-SL structure was also grown on a semi-insulating (SI)-GaAs substrate to study the contribution of the substrate to the carrier density in the SL layers. Temperature dependent Hall effect measurements showed that the nominally undoped structure presented both n-type and p-type conductivities; however, the temperature at which the carrier type switched polarity was observed to be at higher values when the i-SL structure was grown on the SI-GaAs substrate. In addition, a higher carrier density was observed for i-SL on the GaSb substrate than on the GaAs substrate.

In this article, we report on the molecular beam epitaxy growth and characterization of a 140 period InAs/GaSb type-II superlattice structure designed for mid infrared detection. Thickness of a period was systematically altered in each sample by changing the thickness of InAs (GaSb) layers from 9 to 7 monolayers (ML) for a fixed GaSb (InAs) layer at 9 ML (7 ML). The same InSb-like strain compensation interface was used for all samples. High resolution X-ray diffraction analysis, spectral responsivity and external quantum efficiency (QE) measurements were performed to express the effects of layer thickness variations on both structural and photodetector features. The decrease in the InAs thickness resulted in the increased mismatch from 0 to +1626ppm and the blue shift in the 50% cut-off wavelength (λc) from 5.41 to 4.36μm at 77K. The additional decrease in GaSb thickness caused further increase in the mismatch up to +1791ppm. The steepness of the photoresponse at the absorption band edge was quantified and presented comparatively with different photodetector parameters and material properties for a complete picture. The highest optical response was obtained from sample having 8 ML InAs and 9 ML GaSb with λc=4.76μm and QE=23.7% at 4μm.

The effect of four different cooling receipts on the surface morphologies of unintentionally-doped GaSb epilayers on GaSb (100) substrates grown by molecular beam epitaxy is reported. Those receipts include three different Sb beam equivalent pressure (BEP) levels and two different termination temperatures. Surface morphologies of epilayers were examined by wet etching, surface profiler, atomic force microscopy, scanning electron microscopy and Raman spectroscopy. The results demonstrate that during the cooling period, a Sb BEP of 4.00×10−4Pa at a termination temperature of 400°C induces a smooth surface without Sb condensation whereas same Sb BEP at a termination temperature of 350°C forms a 300nm thick Sb layer on the surface. In addition, it is revealed that by applying a wet etching procedure and using a surface profiler it is possible to identify this condensed layer from the two-sloped feature of mesa profile.

The authors describe the noise characterization of a mid-wavelength-infrared (MWIR) photodiode based on indium arsenide and gallium antimonide (InAs/GaSb) superlattice (SL), addressing the influence of different passivation layers applied to the surface of the device. The MWIR InAs/GaSb SL design structure is based on p-i-n configuration grown by the molecular beam epitaxy on a (001) n-GaSb substrate. The SiO 2 -passivated SL photodiodes demonstrated a Schottky-limited noise up to a bias voltage of -0.1 V where the measured peak responsivity is 1.37 AAV with a cut-off wavelength of 4.9 μm and the specific detectivity as high as 1.23 × 10 12 cm. Hz 1/2 /W, demonstrating the high quality of the fabricated MWIR SL photodiodes. The noise measurements exhibited a frequency-dependent plateau (i.e., 1/f noise) for unpassivated and Si 3 N 4 -passivated samples, whereas 1/f-type noise suppression (i.e., frequency-independent plateau) with a noise current reduction at about 30 Hz of more than one order of magnitude was observed for the SiO 2 -passivated ones.

In this study, we report on the investigation of two multilayer GaAs/AlGaAs quantum well infrared photodetectors designed for 8-12 µm spectral range detection. Fabricated devices were characterized by current-voltage and photoresponse measurements as a function of applied bias. Background-limited infrared performance (BLIP) temperatures were performed to determine the optimum bias value for photoresponse for each detector. Photoresponse measurements clearly presented that both devices have responses at the expected spectral region; 8-12 µm.