Deployment of photovoltaics in space requires devices that combine high-efficiency, low areal mass, and resilience to harsh environments. Historically, high-efficiency multijunction III-V materials have dominated space power systems; however, their high cost and limited manufacturing throughput motivate the exploration of scalable alternatives. While CdTe-based thin-film photovoltaics offer an attractive option, their performance on non-conventional substrates can suffer from front contact instability under higher-temperature processing. Here, the role of front contact chemistry in limiting cell performance is investigated using CdTe-based devices fabricated on 150 mu m thick Ceria-doped space-qualified 0214 Corning glass. A matrix of four transparent conducting oxides (TCOs: CTO, AZO, ITO, IZO) combined with two n-type emitters (MZO, IGO) reveals chemical stability at the front interface-rather than absorber composition alone-governs recombination losses, voltage deficits, and device reproducibility. Chemically stable front contact combinations suppress elemental diffusion and interfacial degradation, resulting in significantly improved carrier lifetimes and junction quality. These insights are validated through record-certified Cd(Se,Te) cell efficiencies of 18.4% under AM1.5G and 16.2% under AM0 illumination on ultra-thin glass. Beyond CdTe, this work provides a general framework for the rational selection of TCO/emitter interfaces in superstrate thin-film photovoltaics, including emerging technologies like metal halide perovskites, while enabling high-efficiency, lightweight photovoltaics for space applications.

The absorber layer thicknesses of tandem photovoltaic devices containing hybrid organic–inorganic lead halide perovskite absorbers are optimized under AM 1.5 and AM 0 solar irradiance using external quantum efficiency (EQE) simulations. Using the EQE modeling approach derived from analysis of ellipsometric spectra collected from complete single-junction perovskite, all-perovskite tandem, and copper indium gallium diselenide (CIGS) thin film solar cells, structural–optical models are developed for two high-efficiency tandem solar cell configurations from their published EQE spectra. These configurations include a superstrate all-perovskite device and a substrate perovskite/CIGS device. These models serve as realistic and practical baselines for optimizing device performance under different circumstances. By increasing the thicknesses of an all-perovskite tandem superstrate device’s wide Eg and narrow Eg absorber layers from 350 and 975 nm to 356 and 1200 nm, the Jsc may be increased from 15.81 to 15.94 mA/cm2 under AM 1.5 illumination. This corresponds to a potential increase in efficiency from 25.83 to 26.05% when using reported open circuit voltage (Voc) and fill factor (FF). Under AM 0, an increase in absorber layer thickness to 310 and 1200 nm increases the Jsc from 18.56 to 19.72 mA/cm2, which corresponds to an increase in efficiency from 30.33 to 32.22%. By increasing the thickness of the perovskite layer in a perovskite/CIGS substrate device from 500 to 615 nm, the Jsc may be increased from 18.84 to 19.65 mA/cm2 assuming AM 1.5 illumination. This change would increase efficiency from 23.74 to 24.76%. Under AM 0 illumination, an increase in the perovskite thickness to 512 nm results in an increase in predicted Jsc from 23.13 to 23.34 mA/cm2. This corresponds to a predicted efficiency increase from 29.15 to 29.41%. This modeling approach provides a stable platform for practical evaluation of different superstrate and substrate design tandem solar cells with perovskite semiconductors as at least one of their absorber layers.

We present a comprehensive optical characterization of 200-nm-thick CrN(111) films grown simultaneously on Al_2O_3(0001) and AlN/Al_2O_3(0001) using plasma-assisted molecular beam epitaxy. Spectroscopic ellipsometry, spanning the far-infrared to ultraviolet range (0.04 - 5.5 eV), is conducted at room temperature to determine the optical constants n and k of the films. Spectral fits reveal two interband transitions at approximately 0.35 and 0.60 eV. In the infrared range, the ellipsometry data also reveals a pronounced Reststrahlen band stemming from transversal and longitudinal optical phonons at approximately 403 and 629 cm^-1, respectively. The relative static and high-frequency permittivities are estimated to be about 39 and 15, respectively. A Born effective charge of approximately 2.7, extracted from the far-infrared region, indicates that CrN is partially ionic.

Anisotropic optical properties of single crystal Al2O3 and atomic layer deposited (ALD) thin film alumina have been studied from 0.42 meV to 8.5 eV using spectroscopic ellipsometry. Generalized spectroscopic ellipsometry is used to obtain the complex dielectric function (epsilon = epsilon(1) +/- i epsilon(2)) and complex refractive index (N = n + ik) spectra of Al2O3 single crystals for electric fields oscillating parallel (extraordinary) and perpendicular (ordinary) to the optic axis from the terahertz (THz) to vacuum ultraviolet (VUV) spectral ranges. Spectra in epsilon in the infrared (IR) spectral range show four transverse optical (TO) phonon modes at 385.5, 441.1, 568.6, and 633.1 cm(-1) and four longitudinal optical (LO) phonon modes at 386, 481.5, 629, and 903.34 cm(-1) along the ordinary direction. Two TO modes at 400.1 and 583.9 cm(-1) and two LO phonon modes at 510.79 and 887.209 cm(-1) are observed in the extraordinary direction. Birefringence is similar to 0.011 in the near-IR to VUV and similar to 0.34 in the THz spectral ranges. The refractive index (n) for amorphous ALD thin film alumina is smaller than that obtained for both directions of single crystal alumina, except from similar to 6.8 to 7.6 eV where n for ALD alumina is greater due to an absorption onset at lower photon energies and Kramers-Kronig consistency. The single IR vibrational mode observed at 586 cm(-1) for the ALD film is broader and has a smaller amplitude than that for all TO phonon modes observed for single crystal alumina along both principal directions.

Spectroscopic ellipsometry (SE) has been evaluated for the analysis of silicon photodiodes (PDs), employing instruments spanning the spectral regions of the ultraviolet-to-near-infrared (UV–Vis–NIR: 0.75–5.90 eV), near-infrared-to-mid-infrared (NIR–Mid-IR: 0.45–0.75 eV), and terahertz (THz: 0.10–1.02 THz). In this study, two PDs were chosen for their significantly different spectral responses, and the structural and optical characteristics of their components were determined by SE performed at multiple angles of incidence without contacting the devices. Applying a model of a uniform p+-layer at the front of the PD, analyses of SE data acquired individually over the UV–Vis–NIR SE and NIR–Mid-IR regions yield layer thicknesses and hole concentrations that are in good agreement. Differences in these characteristics can be attributed to variations in the shapes of the doping profiles for the two PDs and the depth sensitivities of the spectral regions. The most informative spectral region is the THz, which provides p+-layer hole concentration profiles and related hole mobilities, as well as the underlying lightly doped bulk Si thicknesses, electron concentrations, and mobilities. The hole concentration profiles from THz SE analysis identify the thickness from the UV–Vis–NIR SE analysis as the depth at which the concentration drops by factors of ∼(2–5) × 10−3. The p+-layer hole concentrations from the UV–Vis–NIR are consistent with depth-averaged values from THz SE to within ∼20% or better for these PDs. This comparison demonstrates that SE, even over the standard UV–Vis–NIR range, is applicable for the non-invasive evaluation of PD structures in manufacturing environments.

Abstract In order to power spacecraft in low earth orbit (LEO), the assessment of performance and stability over a wider temperature range than that encountered terrestrially is required. To this end, state-of-the-art all-perovskite tandem solar cells, attractive for their high power to mass ratio and radiation tolerance, were subjected to temperature extremes from –100 to +100 °C while utilizing maximum power point tracking (MPPT) to assess the in-operando performance under simultaneous thermal cycling and AM0 illumination. These findings show that the wide band gap (WBG) subcell tuned to maximize power output with AM0 illumination undergoes severe phase segregation at temperatures above 50 °C, with only partial recovery within the 45-min dark cooling portion of the thermal cycling, resulting in greatly increased nonradiative recombination and current loss. Although carrier extraction is limited in the narrow band gap (NBG) mixed lead–tin perovskite subcell at low temperatures, this subcell is less prone to thermal instabilities under illumination, making it an attractive candidate for space power systems. Additionally, low-temperature photoluminescence (PL) and MPPT measurements are consistent with luminescence coupling between the WBG emission and NBG absorption, which is beneficial for increased power generation.

Tantalum dioxide (TaO2) is a metastable tantalum compound. Here, we report the epitaxial stabilization of TaO2 on Al2O3 (1102) (r-plane sapphire) substrates using suboxide molecular-beam epitaxy and thermal laser epitaxy, demonstrating single-oriented, monodomain growth of anisotropically strained thin films. Microstructural investigation is performed using synchrotron x-ray diffraction and scanning transmission electron microscopy. The tetravalent oxidation state of tantalum is confirmed using x-ray absorption and photoemission spectroscopy as well as electron energy-loss spectroscopy. Optical properties are investigated via spectroscopic ellipsometry and reveal a 0.3 eV Mott gap of the tantalum 5d electrons. Density-functional theory and group theoretical arguments are used to evaluate the limited stability of the rutile phase and reveal the potential to unlock a hidden metal-insulator transition concomitant with a structural phase transition to a distorted rutile phase, akin to NbO2. Our study expands the understanding of tantalum oxides and paves the way for their integration into next-generation electronic and photonic devices.

Wide band gap FA0.8Cs0.2Pb(I0.6Br0.4)3 perovskite photovoltaic (PV) devices are measured by spectroscopic ellipsometry in the through-the-glass configuration and analyzed to determine the complex optical property spectra of the perovskite absorber as well as the structural properties of all constituent layers. This information is used to simulate external quantum efficiency (EQE) spectra, to calculate PV device performance parameters such as short circuit current density, open circuit voltage, fill factor, and power conversion efficiency, and to develop strategies for increasing the accuracy of predictions. Simulations and calculations tend to overestimate PV device performance parameters, undermining the accuracy and usefulness of those simulations. Mapping spectroscopic ellipsometry measurements of an incomplete device are also collected from the perovskite film side to obtain layer thicknesses, perovskite band gap energies, and Urbach energies at each mapping point. The incomplete device stacks feature the perovskite absorber as the final deposited layer, while the complete devices add electron transport layers and silverback electrical contacts. When simulations are based on structural and optical properties obtained from spectroscopic ellipsometry measurements of incomplete PV device stacks, further inaccuracies arise as characteristics of the exposed perovskite film are not necessarily the same as those of an absorber in a complete, protected PV device. Predictions for PV performance parameters fall within 5% of the experiment for three of four baseline devices. The usefulness of this is apparent in situations where experimentally measuring PV device performance is unfeasible or overly tedious, as well as during intermediate steps during production.

We demonstrate the epitaxial growth of tetragonal platinum monoxide (PtO) on MgO, TiO2, and β-Ga2O3 single-crystalline substrates by ozone molecular-beam epitaxy. We provide synthesis routes and derive a growth diagram under which PtO films can be synthesized by physical vapor deposition. A combination of electrical transport and photoemission spectroscopy measurements, in conjunction with density functional theory calculations, reveal PtO to be a degenerately doped p-type semiconductor with a bandgap of Eg ≈ 1.6 eV. Spectroscopic ellipsometry measurements are used to extract the complex dielectric function spectra, indicating a transition from free-carrier absorption to higher photon energy transitions at E ≈ 1.6 eV. Using tetragonal PtO as an anode contact, we fabricate prototype Schottky diodes on n-type Sn-doped β-Ga2O3 substrates and extract Schottky barrier heights of ϕB > 2.2 eV.

Early progress in advancing the record efficiency of perovskite (PVSK) solar cells was made using the n-i-p structure with spiro-OMeTAD as the hole transport layer (HTL). However, only moderate performance has been achieved with spiro-OMeTAD as the HTL in the p-i-n structure. In this work we investigate the growth of alumina by atomic layer deposition (ALD) on a spiro-OMeTAD HTL and show improved perovskite film growth when the deposition is optimized. The film growth and device performance were examined with current-voltage analysis, scanning electron microscopy, X-ray diffraction, steady-state and time-resolved photoluminescence, Fourier transform infrared spectroscopy, and spectroscopic ellipsometry. When the ALD process was optimized, high-quality perovskite films were produced that led to a doubling in the average device efficiency of the p-i-n device with spiro-OMeTAD as the HTL. The improvements are attributed to better PVSK film growth rather than to significant reductions in nonradiative recombination.

Narrow bandgap organic-inorganic lead halide-based perovskites have attracted tremendous attention in photovoltaics due to their advantages of low cost, easy synthesis and high efficiency. Selection of suitable charge transport layers and evaluation of device stability and optimization is necessary for commercialization. Degradation of encapsulated narrow bandgap tin-lead perovskite solar cells made with poly(3,4ethylenedioxythiophene): polystyrenesulfonate (PEDOT:PSS), poly[3-(6-carboxyhexyl)thiophene-2,5-diyl] (P3CT), and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) hole transport layers (HTLs) in ambient air is investigated using spectroscopic ellipsometry measurements. Optical and structural properties of the perovskite absorber layer remain relatively stable after 10 days of aging in ambient air. External quantum efficiency (EQE) simulations based on spectroscopic ellipsometry determined models identify carrier collection losses when compared with experimental EQE. A fresh device with P3CT HTL has 90 +/- 1 % collection of photogenerated carriers in the perovskite absorber near the front contact interface. 3-, 5-, and 10-days aged devices with P3CT have 88 +/- 1 % collection probability near the front contact interface. Fresh and 3-days aged devices with PEDOT:PSS HTL have 90 +/- 1 % collection of photogenerated carriers in the perovskite absorber near the front contact interface. 5- and 10-days aged devices have 88 +/- 1 % near the front contact interface. Fresh, 3-, 5-, and 10-days aged devices with PTAA HTL have 82 +/- 1 % collection near the front contact interface. Devices with P3CT and PEDOT:PSS HTLs have 2.6 to 4.8 % higher power conversion efficiency and reduced electronic losses compared to a device with a PTAA HTL. Understanding how carrier collection losses, particularly near the front and back contacts, varies with different HTLs is necessary for optimizing perovskite solar cell performance.

Fused silica is used for a variety of applications due to its high transparency, low thermal expansion, and excellent chemical and thermal stability. Ellipsometric spectra of fused silica glass are collected from three different instruments from the terahertz (0.4 meV) to the vacuum ultraviolet (8.5 eV) range and are modelled simultaneously. Unpolarized transmittance is used to quantify low values of absorption from 0.032 to 8.5 eV. A continuous parameterization of complex dielectric function (ɛ = ɛ1 + iɛ2) spectra from 0.4 meV to 8.5 eV is developed.

We utilize a combined computational-experimental approach to examine the influence of indium nanoparticle (NP) array distributions on deep-ultraviolet (UV) plasmon resonances. For photon energies < 5.7 eV, analysis of ellipsometric spectra reveals an increase in silicon reflectance induced by indium NP arrays on silicon. For various energies in the range 5.7–7.0 eV, a decrease in reflectance is induced by the NP arrays. Similar trends in reflectance are predicted from finite-difference time-domain (FDTD) simulations using NP size distributions extracted from atomic-force micrographs as input. In addition, in the energy range of 7.4–9.2 eV, the FDTD simulations reveal reflectance minima, characteristic of localized surface plasmon resonances. Electron energy-loss spectroscopy collected from individual indium NPs reveals the presence of LSPR at ≈ 8 eV, further supporting the promise of indium NP arrays on silicon for deep-UV plasmonics.

Indium gallium oxide [(InxGa1−x)2O3] alloys are of interest for a variety opto-electronic applications including photovoltaic devices owing to the ability to control properties through alloy composition. A thorough evaluation of the opto-electronic properties of (InxGa1−x)2O3 (x = 0.71, 0.55, 0.45, 0.36, and 0.28) thin films is obtained by using terahertz to ultraviolet range spectroscopic ellipsometry to measure the complex dielectric function (ɛ = ɛ1 + iɛ2) spectra from 0.400 meV to 5.877 eV and the derived vibrational modes from chemical bonding, inter-band transition energies, and carrier transport properties. Optical band edges of direct and non-direct transitions increase from 3.82 to 4.14 eV and 2.96 to 3.36 eV, respectively, with decreasing In-content, whereas the carrier concentration determined from the direct electrical Hall effect and spectroscopic ellipsometry measurements decreases from ∼1020 to 1018 cm−3. Mobilities (μSE), resistivities (ρSE), and carrier effective masses (m*SE) from the spectroscopic ellipsometry range from ∼10.6 to ∼66.8 cm2 V−1 s−1, 2.3 × 10−3, to 47.1 × 10−3 Ω cm, and 0.308 to 0.397 me, respectively. μSE and ρSE are compared to those obtained from the direct electrical Hall effect and four-point probe measurements with discrepancies attributed to principles of measurement techniques. Spectroscopic ellipsometry determined parameters are representative of properties within localized regions, whereas direct electrical measurements are influenced by a greater degree of charge carrier scattering due to longer path lengths of travel.

Carrier concentration (N) of indium tin oxide (ITO), poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), and low bandgap perovskite (FASnI3)0.6(MAPbI3)0.4 in the photovoltaic device configuration are determined using terahertz (THz) spectral range optical Hall effect measurements and analysis. Unlike direct electrical Hall effect, this technique is non-invasive as it does not need any direct electrical contacts and is able to probe free carrier transport properties of individual films inside the device stack. A modified Drude model is implemented to address the dominating free carrier absorption in the THz spectral range. N of the ITO, PEDOT: PSS, and (FASnI3)0.6(MAPbI3)0.4 are determined to be (2.8 +/- 0.6) x 1020 cm-3, (2.6 +/- 0.8) x 1022 cm-3, and (1.5 +/- 0.1) x 1018 cm-3, respectively. PV device performance is simulated with SCAPS employing the findings from optical Hall measurements. Open circuit voltage (VOC), short circuit current (JSC), fill factor (FF), power con-version efficiency (PCE) are found to be 0.865 V, 29.2 mAcm-2, 66.7%, and 16.8% respectively which are within 3% of corresponding experimentally measured values. These optically measured N serve as essential parameters for device modeling to understand its physics in device performance and to optimize PCE; consistency between simulated and experimental device performance parameters using these values supports optical Hall effect as a reliable technique to extract electronic transport properties.

In -situ real-time spectroscopic ellipsometry (RTSE) measurements are performed on a growing amorphous vanadium oxide (a-VO x ) film to determine the complex dielectric function ( e = e 1 + i e 2 ) spectra, structure, and oxygen content ( x ) with depth during deposition. VO x with x -2 is annealed to produce polycrystalline VO 2 and characterized by near -infrared to ultraviolet (0.75 - 5.9 eV) spectroscopic ellipsometry during heating and cooling from room temperature (RT) to 343 K to RT to track hysteresis effects in the semiconducting -to -metal transition (SMT). Spectra in e are measured for as -deposited and annealed films prepared with varying deposition parameters to determine the as -deposited film x and verify the SMT. Temperature -dependent IR extended spectroscopic ellipsometry is performed from 0.06 to 0.74 eV to determine the IR e spectra of polycrystalline VO 2 across the SMT. As -deposited amorphous VO x films with x from 1.89 <= x <= 2.14 transition to polycrystalline VO 2 after annealing and exhibit the SMT when heated from RT to 343 K which are verified by substantially increased e 2 magnitude at >= 343 K. By identifying x of a-VO x from e spectra, a shortened path of qualifying a-VO x films which will crystallize to phase change VO 2 is developed.

An in-depth analysis of the optical properties of epitaxial (001) oriented LaMnO3films grown on SrTiO3and LaAlO3single crystal substrates is performed by spectroscopic ellipsometry to determine the complex dielectric function (ε = ε1 + iε2) spectra from 0.12 to 5.89 eV. Density Functional Theory and many body perturbation theory within the G0W0 and the Bethe-Salpeter Equation approximations, are also employed to generate theoretical spectra in ε. Critical point energies (CPs) from 0.91 to 1.49 eV are interpreted as energy separation between eg and t2g orbitals. CPs from 3.31 to 3.53 eV and 3.75 to 5.23 are interpreted as Mn d exchange splitting and strong charge transfer transitions, respectively. Direct and indirect bandgaps from Tauc-plots are identified in the range of 0.100–0.594 eV. Anisotropy presents in LaMnO3 on LaAlO3 is attributed to substantial distortion in the out-of-plane epitaxial strain compared to LaMnO3 on SrTiO3. These findings provide a comprehensive understanding of the origins and characteristics of features observed in optical properties of epitaxial LaMnO3, offering insights for development of optical and electronic applications based on these materials.

Complex dielectric function (ɛ = ɛ1 + iɛ2) spectra of a heat treated single crystal yttria-stabilized zirconia (YSZ) have been determined over a spectral range of 0.03–8.5 eV using spectroscopic ellipsometry. Spectra are collected using three instruments covering different parts of the measured spectrum. The YSZ sample is modeled as a semi-infinite bulk crystal covered by a surface layer described by a Bruggeman effective medium approximation of equal parts YSZ and void.

Determining exactly how the performance of a thin-film photovoltaic device is limited by a particular recombination mechanism can be difficult, particularly in the case of CdTe solar cells. As a result, efforts are being made to improve all parts of the device without good knowledge of which improvements are necessary. To understand where the device limitation is, the recombination current densities of at least one on of the interfaces must be known. Here, we present a method to determine which recombination mechanisms is limiting. First, back illuminated quantum efficiency measurements are used to determine the key parameters of the back interface – the back surface recombination velocity and the band bending near the back surface. Once these back interface parameters are determined, the recombination current densities can be calculated for a front illuminated device to determine the limiting mechanism. The validity of the approach is tested using previously reported data.