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The mechanisms of sputter induced stress and damage in perovskite/silicon tandem solar cells were investigated for optimizing buffer layer materials and transparent conductive oxides. A high power conversion efficiency of 26.0% has been achieved.

The efficiency of all-perovskite tandem devices falls far below theoretical efficiency limits, mainly because a widening bandgap fails to increase open-circuit voltage. We report on a bifacial all-perovskite tandem structures with an equivalent efficiency of 29.3% under back-to-front irradiance ratio of 30. This increases energy yield and reduces the required bandgap of a wide-bandgap cell. Open-circuit voltage deficit is therefore minimized, although its performance under only front irradiance is not ideal. The bifacial device needs a sputtered rear transparent electrode, which could reduce photon path length and deteriorate stability of Pb-Sn perovskites. Embedding a light-scattering micrometer-sized particle layer into perovskite to trap light, effectively increases absorptance by 5 to 15% in the infrared region. Using a nonacidic hole transport layer markedly stabilizes the hole-extraction interface by avoiding proton-accelerated formation of iodine. These two strategies together increase efficiency of semitransparent Pb-Sn cells from 15.6 to 19.4%, enabling fabrication of efficient bifacial all-perovskite tandem devices.

Minimizing module heating is an effective way to increase the lifetime energy output of photovoltaic systems. Maximizing the reflection of light that is unusable for energy conversion is one of the most promising ways to reduce the operating temperature of fielded modules. We derive a model based on a steady-state energy balance to quantify the temperature benefit of cell or module optical modifications aimed at improving reflection of light with photon energies below the photovoltaic cell bandgap energy. This more detailed model is then simplified so that, from outdoor measured data, temperature differences arising from reflectance can be isolated from those arising from irradiance, wind speed, and module standard-test-condition efficiency.

We report spectrally selective visible wavelength reflectors using hydrogenated amorphous silicon carbide (a-SiC:H) as a high index contrast material. Beyond 610nm and through the near infrared spectrum, a-SiC:H exhibits very low loss and exhibits an wavelength averaged index of refraction of n = 3.1. Here we design, fabricate, and characterize such visible reflectors using a hexagonal array of a-SiC:H nanopillars as wavelength-selective mirrors with a stop-band of approximately 40 nm full-width at half maximum. The fabricated high contrast grating exhibits reflectivity R >94% at a resonance wavelength of 642nm with a single layer of a-SiC:H nanopillars. The resonance wavelength is tunable by adjusting the geometrical parameters of the a-SiC:H nanopillar array, and we observe a stop-band spectral center shift from 635 nm up to 642 nm. High contrast gratings formed from a-SiC:H nanopillars are a promising platform for various visible wavelength nanophotonics applications.

Summary Nickel oxide (NiOx) hole transport layers (HTLs) are desirable contacts for perovskite photovoltaics because they are low cost, stable, and readily scalable; however, they deliver lower open-circuit voltages (VOCs) compared to organic HTLs. Here, we characterize and mitigate electron transfer-proton transfer reactions between NiOx HTLs and perovskite precursors. Using XPS and UPS characterization, we identify that Ni≥3+ metal cation sites in NiOx thin films act both as Bronsted proton acceptors and Lewis electron acceptors, deprotonating cationic amines and oxidizing iodide species, forming PbI2−xBrx-rich hole extraction barriers at the perovskite-NiOx interface. Titrating reactive Ni≥3+ surface states with excess A-site cation salts during perovskite active layer deposition yielded an increase in VOC values to 1.15 V and power conversion efficiencies of ∼20%. This may be a general finding for metal oxide contacts that act as Bronsted and Lewis acid-base reactants toward perovskite precursors, an observation that has also been made recently for TiO2 and SnO2 contacts.

The efficiencies of all-perovskite tandem devices are improving quickly. However, their complex interconnection layer (ICL) structures—with typically four or more layers deposited by different processes—limit their prospects for applications. Here, we report an ICL in all-perovskite tandem cells consisting merely of a fullerene layer and a SnO2–x (0

Luminescent solar concentrators are currently limited in their potential concentration factor and solar conversion efficiency by the inherent escape cone losses present in conventional planar dielectric waveguides. We demonstrate that photonic crystal slab waveguides tailored for luminescent solar concentrator applications can exhibit >90% light trapping efficiency. This is achieved by use of quantum dot luminophores embedded within the waveguide that absorb light at photon energies corresponding to photonic crystal leaky modes that couple to incoming sunlight. The luminophores then emit at lower photon energies into photonic crystal bound modes that enable highly efficient light trapping in slab waveguides of wavelength-scale thickness. Photonic crystal waveguides thus nearly eliminate escape cone losses, and overcome the performance limitations of previously proposed wavelength-selective dielectric multilayer filters. We describe designs for hole-array and rod-array photonic crystals comprised of hydrogenated amorphous silicon carbide using CdSe/CdS quantum dots. Our analysis suggests that photonic crystal waveguide luminescent solar concentrators using these materials these can achieve light trapping efficiency above 92% and a concentration factor as high as 100.

Summary Integrating perovskites onto textured silicon provides a pathway to 30% tandem solar cells. However, deposition of 0.5–1 μm thick perovskite layers from solution onto textured silicon with typical pyramid heights of 3–10 μm remains a challenge. We propose a new tandem architecture that enables scalable, solution-based blading of perovskites onto silicon wafers textured with pyramids less than 1 μm in height. These pyramids are rough enough to scatter light within the silicon nearly as efficiently as large pyramids but smooth enough to solution-process a perovskite film. A nitrogen-assisted blading process deposits both a conformal hole transport layer and a planarizing perovskite layer that fully covers the textured silicon, at a speed of 1.5 m/min. With a textured light-scattering layer added to the top of the tandem to reduce front-surface reflectance, we achieve a perovskite/silicon tandem cell with an efficiency of 26% on textured silicon.

Tuning band gaps with three halides Tandem solar cells can boost solar cell efficiency by using two active layers to absorb the solar spectrum more completely, provided that the two cells are current-matched. Inorganic-organic perovskites tuned to the appropriate wide band gap (∼1.7 electron volts) as top cells that contained iodine and bromine or bromine and chlorine have short carrier diffusion lengths and undergo photo-induced phase segregation. Xu et al. now report a method for incorporating chloride that allows for fabrication of stable triple-halide perovskites with a band gap of 1.67 electron volts. Two-terminal tandem silicon solar cells made with this material had a power conversion efficiency of 27%. Science , this issue p. 1097

Summary Combining the higher energy yield of bifacial photovoltaic modules with the higher efficiency of silicon-based tandem devices is a promising pathway to reduce the levelized cost of electricity of photovoltaic systems. In a two-terminal bifacial tandem, the additional photon flux on the back of the bottom cell alters the current matching between the cells. This study quantifies this phenomenon, starting with spectrally resolved front and back irradiances determined from ray tracing under realistic conditions. A tandem-device model is then used to explore the impact of different scenarios on the optimal top-cell bandgap and power production. Although the energy gains from bifacial tandem systems are small, the range of suitable top-cell bandgaps is greatly broadened, thus widening the window of absorber candidates. In one exemplary case, a bifacial tandem with a top-cell bandgap as low as 1.63 eV retains the energy output of an optimized monofacial tandem with a 1.71-eV top cell.

In silicon heterojunction solar cells, optimization of the front transparent conductive oxide (TCO) layer is required in order to minimize both electrical and optical losses. In this article, design guidelines for this overall power loss minimization are presented—extending previous TCO optimization work that was limited to the maximization of the short-circuit current density alone—and these are used to prescribe the best TCOs for both single-junction and silicon-based four-terminal tandem applications. The employed procedure determines the loss associated with the front TCO layer as a function of the TCO carrier density, mobility, and thickness, as well as the pitch between the front electrode fingers. For a representative indium tin oxide (ITO) film with a mobility of approximately 20 cm2·V−1·s−1 and a carrier density of 2.5 × 1020 cm−3, the loss over the 700–1200 nm infrared wavelength range—the spectrum reaching the silicon bottom cell in a typical tandem structure—is minimized by using a finger pitch of 3 mm and an ITO thickness of 100–110 nm. This compares with an optimal finger pitch of 2 mm and an optimal ITO thickness of 70 nm for the same cell operating as a single-junction device under full spectrum. The methodology presented can also readily be applied to TCO materials other than ITO, to a wide variety of specific four-terminal tandem architectures and, with minor modifications, to rear TCO layers.

Unique properties can be achieved in engineered nanoparticle films, including those related to quantum confinement, surface chemistry, and light propagation, which can be exploited for energy appli...

The manipulation and characterization of light polarization states are essential for many applications in quantum communication and computing, spectroscopy, bioinspired navigation, and imaging. Chiral metamaterials and metasurfaces facilitate ultracompact devices for circularly polarized light generation, manipulation, and detection. Herein, we report bioinspired chiral metasurfaces with both strong chiral optical effects and low insertion loss. We experimentally demonstrated submicron-thick circularly polarized light filters with peak extinction ratios up to 35 and maximum transmission efficiencies close to 80% at near-infrared wavelengths (the best operational wavelengths can be engineered in the range of 1.3–1.6 µm). We also monolithically integrated the microscale circular polarization filters with linear polarization filters to perform full-Stokes polarimetric measurements of light with arbitrary polarization states. With the advantages of easy on-chip integration, ultracompact footprints, scalability, and broad wavelength coverage, our designs hold great promise for facilitating chip-integrated polarimeters and polarimetric imaging systems for quantum-based optical computing and information processing, circular dichroism spectroscopy, biomedical diagnosis, and remote sensing applications., Metasurfaces: Inspired by nature Inspired by the polarization-sensitive vision of the compound eyes in a marine crustacean called the Mantis Shrimp, researchers from Arizona State University, US have designed a chiral metasurface for manipulating the polarization of light. The metasurface design consists of a thin nanostructured silicon layer, a dielectric spacer layer and a gold nanowire polarizer, and has a total thickness of less than 1 micrometer. This thin planar surface offers low optical loss with a transmission as high as 80% in the near-infrared wavelength range, and acts as a circular polarization filter with an extinction ratio as high as 35. The circular polarization filters, in combination with linear polarization filters, can enable chip-scale polarimeters for sensing the polarization state of light. This on-chip integrated approach could prove useful in ultra-compact devices for advanced imaging and sensing applications.

Mg x Zn 1-x O (MZO) has recently gained popularity as a transparent electron contact in CdTe-based solar cells. The value of the conduction band offset (CBO) and, hence, of the MZO bandgap are often considered essential parameters of this interface, as—in theory—the CBO has a strong impact on both the conduction of electrons and the recombination of holes. However, in this contribution, we report MZO/CdSeTe interfaces where recombination appears to be independent of the CBO. The implications of such results are discussed.

In this contribution, we investigate why different dopant species and back-contact architectures lead to different sub-bandgap behaviors in CdSeTe solar cells. Through extraction of the absorptance from photoluminescence spectra, we parse the contributions from material properties and from cell optics. We show that, as expected, arsenic doping leads to an increase in sub-bandgap features over traditional copper doping, and that this is a material property of arsenic-doped CdSeTe. Conversely, the increase in sub-bandgap absorption and emission using alternative back contact architectures can be attributed to the cell optics, and more specifically to the increased reflectance of the back interface, leading to at least a doubling of the pathlength for sub-bandgap photons.

Anti-reflection coatings are used on 92% of today’s module glass to reduce the front-surface reflection and increase the power output of the module. Currently, most anti-reflection coatings are designed to maximize transmittance at normal incidence to improve the power output at standard test conditions. However, in the field, where the meteorological conditions vary widely in time and space, it is not clear whether a maximum power gain at standard test conditions leads to maximum energy yield. Here, we use SunSolve Yield, a ray-tracing software, to investigate the optimum anti-reflection coating design by simulating the energy yield from a PV system under real-world conditions. We found that manufacturers could immediately provide a 0.3% increase in energy yield relative to their products today by simply increasing the ARC thickness by 20–40 nm thicker.

We observe a degradation of the minority-carrier lifetime in silicon substrates after a temperature cycle in a molecular beam epitaxy (MBE) chamber that is representative of the growth of III–V materials. This decrease in the lifetime is from milliseconds to microseconds, and in some cases into the sub-microsecond range. The degradation appears to be caused by thermally activated diffusion of metals from the back side of the substrate, occurring at temperatures above 500 °C. This impacts the ability to achieve high-performance monolithic III–V/Si multi-junction solar cells, since the epitaxial growth usually requires high-temperature steps (over 700 °C) for surface de-oxidation or surface reconstruction and temperatures of 400–600 °C during the epitaxial growth. We show that, through phosphorous diffusion gettering, the lifetimes of degraded wafers can be recovered to the millisecond range. Further, we demonstrate that a silicon nitride coating functions both as a diffusion barrier and as an interfacial gettering or hydrogenation agent, enabling high minority-carrier lifetimes directly out of the MBE chamber. This approach allows for the silicon minority-carrier lifetime to be maintained in the millisecond range without the need for post-growth recovery, providing a path to achieve high-efficiency III–V/Si solar cells.

We investigated the effect of GaAs y P 1-y graded buffer layer design and cell structure on GaAsP solar cells grown on GaP/Si templates. Heavy Si doping in the graded buffer layer increases threading dislocation density (TDD) by 2.7× compared to no doping, while heavy Be doping has little or no effect on TDD. Higher TDD increases the bandgap-voltage offset, but its effect on short-circuit current density is more complex. For example, by implementing an n+/i/p structure in cells with elevated TDD, we could obtain significantly higher internal quantum efficiencies at 500–750 nm compared to n+/p structures with low TDD. All cells investigated here achieved efficiencies of 15.5-15.9% despite TDD values ranging from 4.5×106-1.2×107 cm−2.

We have demonstrated world-record thermophotovoltaic (TPV) conversion efficiency in two materials systems operating at two different thermal emitter temperatures. A GaAs-based PV device under a 2330 °C thermal emitter produced an efficiency of (31 ± 2)%, and an In 0.53 Ga 0.47 As -based PV device under a 1300 °C thermal emitter produced an efficiency of (30 ± 2)%. The electrical output power densities of the cells were 2.45 W/cm2 and 0.658 W/cm2, respectively. Critical to these high efficiencies were the cells' high reflectance of photon energies below the absorber band gap. Unlike solar PV, for which sub-band gap (SBG) light is lost, a TPV cell can reflect SBG light back to the thermal emitter where it can be recycled. The demonstrations were made on a custom-built measurement platform in which a ~ 100 cm2 graphite thermal emitter was heated under vacuum. The TPV efficiencies were evaluated by comparing the measured electrical output power of the cell with the total power absorbed by the cell. The measured TPV efficiencies as a function of thermal emitter temperature were corroborated by our full system modeling. As far as the authors are aware, these are the highest TPV conversion efficiencies ever measured, and device improvements should yield > 40% efficiency in the near future.

While commonly used in Si solar cell characterization, the Suns– V oc method of determining series resistance (R s ) is rarely used for CdTe and its alloys. However, it is advantageous relative to the slope method–commonly used in the CdTe community–because it measures series resistance at the maximum power point, at which a solar cell operates. Using the self-consistent predecessor to $\mathrm{Suns}-\mathrm{V}_{\mathrm{oc}}, \mathrm{J}_{\mathrm{sc}}-\mathrm{V}_{\mathrm{oc}}$ , we determine $\mathrm{R}_{\mathrm{s}}$ of two different $\mathrm{CdSeTe}/\mathrm{CdTe}$ solar cell structures to be 0.96 and 2.72 μcm2, with repeated measurements showing little deviation.

The first step to understand the origin of losses in any photovoltaic solar cell is to determine the fundamental thermodynamic efficiency and voltage limits of such a device. In this contribution, we detail techniques to calculate the voltage limit in the case of cadmium selenium telluride (CdSeTe) solar cells, and how approaches based on bandgap alone—i.e., the Shockley-Queisser approach with step-function absorptance—can overestimate the thermodynamic open-circuit voltage limit $V_{oc,ideal}$ . This is particularly true for arsenic-doped samples, which tend to exhibit below-bandgap absorptance.

Since excellent carrier lifetimes and front interface electronic quality are now achieved, rear interface recombination can limit V OC in $\text{CdSe}_{\mathrm{x}}\text{Te}_{1-\mathrm{x}}/\text{CdTe}$ solar cells. Several back-contact structures for devices were fabricated using combinations of tellurium, aluminum oxide, amorphous silicon, and indium tin oxide (ITO). Time-resolved photoluminescence was used to characterize such structures. We show increasingly improved interface passivation through the subsequent use of aluminum oxide, amorphous silicon, and ITO. Additionally, we show that arsenic-doped absorbers form a more passive interface with numerous back contact structures.

Integrating perovskites onto textured silicon bottom cells with a scalable solution process is crucial to commercializing perovskite/silicon tandem technology. Here, we propose a new tandem architecture that enables a scalable solution blading process of perovskites on textured silicon. In this tandem architecture, the pyramidal texture is tuned to be less than 1 micron. With this pyramid feature size, the silicon cell surface is rough enough to scatter the light to reduce the reflection loss, but still smooth enough to solution process the perovskite cell. A nitrogen-assisted blading process is then applied to deposit both a conformal hole transport layer and a compact micron-thick perovskite layer to planarize the textured silicon. With additional textured polydimethylsiloxane (PDMS) on the tandem as an antireflection layer, we achieve 26%-efficient perovskite/silicon tandem cells on textured silicon by solution processed perovskite layer, with a short-circuit current density of 19.2 mA/cm2.

Electrically conductive adhesives (ECAs) are being used in several different PV module architectures, including shingled modules. Presently, there is limited available literature on the failure mechanisms of ECAs. X-ray imaging techniques can image a wider region than that of sample extraction for SEM imaging, while still retaining resolutions down to 0.5 µm/pixel. X-ray projections have been used to study the effect of different ECA application methods and curing conditions on the ECA in a shingled mini-module. It was found that lamination does not affect the ECA, if it has already been cured. Additionally, the cell lay-up step in the shingled module fabrication was found to be the primary cause of voids in the ECA layer.

We review recent progress in GaAsP/Si tandem cells and present a GaAsP/Si tandem cell with a high total short-circuit current density of 38.2 mA/cm2. Comparing the external quantum efficiency (EQE) of this tandem cell with benchmark perovskite/Si tandem cells reveals that at identical top cell bandgap, the GaAsP top cell exhibits higher or comparable EQE at all wavelengths, while the GaAsP-filtered Si bottom cell exhibits insufficient light trapping and parasitic absorption. Future improvement in the transparency of the GaAsyP 1- y graded buffer layer and the light trapping in the Si bottom cell promises GaAsP/Si tandem cells with a short circuit density above 20 mA/cm2.

Summary Organic-inorganic halide perovskites are promising semiconductors to mate with silicon in tandem photovoltaic cells due to their solution processability and tunable complementary bandgaps. Herein, we show that a combination of two additives, MACl and MAH2PO2, in the perovskite precursor can significantly improve the grain morphology of wide-bandgap (1.64–1.70 eV) perovskite films, resulting in solar cells with increased photocurrent while reducing the open-circuit voltage deficit to 0.49–0.51 V. The addition of MACl enlarges the grain size, while MAH2PO2 reduces non-radiative recombination through passivation of the perovskite grain boundaries, with good synergy of functions from MACl and MAH2PO2. Matching the photocurrent between the two sub-cells in a perovskite/silicon monolithic tandem solar cell by using a bandgap of 1.64 eV for the top cell results in a high tandem Voc of 1.80 V and improved power conversion efficiency of 25.4%.

Tandem Solar Cells with Silicon as one of its constituents have flat surfaces (surfaces without texturing). That is why flat surfaces Solar cells have got quite importance. But the issue with the flat surfaces is the high reflection loss (flat) and poor light trapping (no-texturing) in the cells. So, some scattering film, other than direct texturing, that is polydimethylsiloxane (PDMS) polymer with the texture is used. The optimized PDMS film here is the random pyramidal film because random pyramidal PDMS films have a drop of 56.6% in reflectance used on polished Silicon while iso-textured and inverted pyramids have 51.55% and 48.47% respectively. This PDMS film with random textures when applied to 2-terminal monolithic perovskite/Silicon tandem, its external quantum efficiency shows an increase of 1.12mA/cm2in the short-circuit current and reflection loss reduces by 4.1 mA/cm2.

The rapid rise in efficiency and tunable bandgap of metal-halide perovskites makes them highly attractive for use in tandems on silicon. Recently we demonstrated a perovskite–silicon monolithic two...

Thin films composed of nanoparticles are used in a variety of applications, from antireflective coatings in photovoltaic modules to antibacterial agents in textiles. In this work, we demonstrate an aerosol-impaction-based process for forming uniform thin films of controllable thickness and porosity on large-area substrates. Through a combination of scanning electron microscopy, Rutherford backscattering, and elliposometry, we demonstrate silicon nanoparticle films with independently tunable thicknesses between 50 nm and 3 μm and porosities between 67% and 95%. We further demonstrate the scalability of this process by forming films with

Tandem photovoltaic modules with silicon bottom cells offer a promising route to exceed the single-junction photovoltaic efficiency limit and further lower the levelized cost of solar electricity. However, it is unclear whether continued improvements in efficiency will render tandem modules cost-competitive with their two constituent sub-cells, and with silicon technology in particular. Here, we construct a simple and versatile techno-economic model that, for a given balance-of-systems scenario, calculates the tandem module efficiency and cost from assumed sub-cell module efficiencies and costs. To understand which input conditions are likely to be representative of the future photovoltaic market, we calculate learning rates for both module and area-related balance-of-system costs, and find that the slower learning rate of the latter means that high-efficiency tandems will become increasingly attractive. Further, in the residential market in 2020, the model indicates that top-cell modules could cost up to US$100 m–2—over twice that of the projected silicon module cost—and the associated tandem module would be cost-competitive if its energy yield, degradation rate, service life and financing terms are similar to those of silicon. One way to overcome the theoretical efficiency limit of silicon photovoltaics is to use them as the bottom cell in a tandem photovoltaic module. Here a model for tandem module efficiency and cost is presented, based on assumed sub-cell efficiencies and costs, and used to examine possible paths for different tandem markets.

To maximize the utilization of solar energy, this study focuses on the investigation of a realistic performance of a photovoltaic/concentrated solar power hybrid using a developed wavelength-selective filter. The hybrid system is proposed for the modification and improvement of the performance of the currently operating solar electric generating station VI parabolic trough plant in California, USA. In the hybrid, photovoltaic system converts only the useful wavelengths after the splitting of the solar irradiance by the wavelength-selective filter, and the concentrated solar power uses the remaining wavelengths. Most relevant studies presented the hybrid performance using hypothetical filters instead of realization. Even studies utilizing realized filters have only used annual mean values to assess hybrid performance. Due to the intrinsic properties in real filters, the hybrid performance can be varied accordingly throughout the day and year. As a result, by presenting annual performance based on the measured optical properties of a real filter, this study intends to address this research gap. According to the findings, the proposed hybrid performed 9% better than the solar electric generating station VI concentrated solar power. The hybrid system was also 4% more efficient than the virtual photovoltaic-alone system. The proposed hybrid’s Levelized Cost of Electricity is 9% lower than the solar electric generating station VI concentrated solar power. Even if the proposed filter accounts for 18.4% annual optical loss from the incident solar power, the proposed hybrid is still very promising for retrofitting and enhancing aged concentrated solar power plants.

This work demonstrates a monocrystalline 1.7 eV Mg0.13Cd0.87Te solar cell with an open-circuit voltage of 1.176 V and an active-area efficiency of 11.2%. The absorber layer is clad in wider bandgap passivation layers that effectively confine electrons and holes via the resulting band offsets. The potential barriers cladding the absorber are generated using higher magnesium compositions than the absorber and provide excellent carrier confinement. This ultimately leads to long minority carrier lifetimes (>500 ns) and high photoluminescence quantum efficiencies yielding an implied open-circuit voltage of 1.3 V. However, the same barriers at the heterointerfaces reduce fill factor by impeding transport; this is apparent as series resistance losses that can be overcome with operation at higher temperatures. The photocurrent loss mechanisms are simulated and analyzed, laying out the pathway for further improvements in current generation and, thus, efficiency.

Magnesium zinc oxide (MZO, MgxZn1-xO) is a leading emitter for CdTe-based solar cells due to its transparency and the ability to tune its conduction band offset with the absorber. Devices employing alloyed cadmium selenide telluride (CST, CdSeyTe1-y) absorbers achieved high efficiency (>19%) using MZO deposited by reactive sputtering over a broad composition range (3.68–3.92 eV, x: 0.20–0.35). Minimal differences in implied and measured open circuit voltage indicate that the contacts are well passivated and highly selective across the spectrum of MZO employed. Device performance insensitivity to MZO composition, which is not observed in CdTe devices, is attributed to the formation of an oxygenated interface layer. Se volatility creates a group VI deficiency at the interface that drives O migration from the MZO into the absorber. This introduces conductivity in the emitter not present in its as-deposited state, contributing to the exceptional performance observed. It is shown that the quality of device passivation depends on the oxidation state of the as-deposited MZO such that intelligent control and management of the reactive sputtering process is required.

Several developing solar cell technologies—including perovskite cells, thin-film cells, epitaxially grown cells, and many tandem cells on silicon—have fabrication constraints that require a planar front surface. However, flat front surfaces result in large reflection losses and poor light trapping within the cell. We investigate scattering layers made from polydimethylsiloxane (PDMS) polymer carrying a random-pyramid texture to reduce such losses. The layers are first tested on a model system consisting of silicon heterojunction solar cells that have zero, one, or two surfaces textured with the same random pyramids (the other surfaces being planar) in order to elucidate the potential and limitations of employing a textured transparent layer instead of a textured absorber. PDMS layers result in short-circuit current density enhancements of 3.0 mA/cm 2 and 1.7 mA/cm 2 when applied to the front of a cell with flat front and rear surfaces, and a cell with a flat front surface and textured rear surface, respectively. Optical simulations reveal that the majority of the gain is due to a reduction in front-surface reflection and that the layers contribute only marginally to trapping weakly absorbed infrared light; nevertheless, a cell with a textured rear surface and a PDMS layer at its flat front surface can come to within 0.7 mA/cm 2 of the performance of a double-side-textured cell. Finally, a PDMS scattering layer is implemented in a planar perovskite solar cell, boosting its short-circuit current density by 1.9 mA/cm 2 and thus its efficiency by 10.6% relative.

As single-junction Si solar cells approach their practical efficiency limits, a new pathway is necessary to increase efficiency in order to realize more cost-effective photovoltaics. Integrating III–V cells onto Si in a multijunction architecture is a promising approach that can achieve high efficiency while leveraging the infrastructure already in place for Si and III–V technology. In this Letter, we demonstrate a record 15.3%-efficient 1.7 eV GaAsP top cell on GaP/Si, enabled by recent advances in material quality in conjunction with an improved device design and a high-performance antireflection coating. We further present a separate Si bottom cell with a 1.7 eV GaAsP optical filter to absorb most of the visible light with an efficiency of 6.3%, showing the feasibility of monolithic III–V/Si tandems with >20% efficiency. Through spectral efficiency analysis, we compare our results to previously published GaAsP and Si devices, projecting tandem GaAsP/Si efficiencies of up to 25.6% based on current state...

We report a monocrystalline CdTe/MgCdTe double-heterostructure solar cell with an a-Si:H hole contact and an ITO/SiO x electrode stack. Similar designs have achieved high open-circuit voltages, but low short-circuit current densities and fill factors have limited the cell efficiencies. We investigate the origin of these losses, and, in addressing some of them, achieve a maximum total-area efficiency of 18.5% and active-area efficiency of 20.3% measured under AM1.5G illumination. Additional cells have been measured with open-circuit voltages of up to 1.11 V, while still maintaining respectable fill factors and no rollover. The lack of rollover, either before or after open circuit, confirms the potential of this approach to reach very high efficiencies. The optical losses within the device are quantified and analyzed across the spectrum to determine if there exists potential for increased current generation through a reduction in parasitic absorption. In addition, fitting the current–voltage characteristic reveals that the leading cause of the less-than-ideal fill factor is series resistance, which contributes a 7% absolute loss.