Abstract. Conventional concentrator photovoltaics (CPV) employing two-axis tracking are generally only economically competitive with cheaper, less efficient alternatives in locations with large amounts of direct sunlight. Adding a diffuse light collector to a CPV panel in the form of a silicon back panel can potentially improve the light collection under cloudy conditions and expand the range of climates in which CPV is useful. However, to understand the performance advantages available with diffuse collection, a realistic forecasting tool to predict performance in different locations is required. We introduce a model to evaluate the annual energy yield of a hybrid CPV and Si module and compare the results with several conventional stand-alone Si and CPV modules. The advantages of including a bifacial Si panel as the diffuse collector will also be investigated.

The Integrated Urban Services (IUS) Program virtual launch event was conducted on August 10th and 12th, 2021 and provided education to the 26 cities in the ASEAN Smart Cities Network focused on integrated urban planning and the energy-food-water nexus. Experts representing academia, government, NGOs, and the private sector were invited to share knowledge and key lessons from their experience working on urban development projects in the ASEAN region and around the world. The IUS program, which is funded by the U.S. State Department and implemented by the National Renewable Energy Laboratory, aims to promote systems integration and circular economy principles for resource recovery and reuse at the city scale. This new initiative will help ASEAN cities build resilience in their energy, water, and food provision systems. The objectives of this three-year project are to: Educate stakeholders on the benefits of circular economy approaches such as resource recovery and reuse, and on opportunities to build cost-efficient and resilient models of basic urban service and food provision; Provide technical assistance to two select cities within ASEAN to aid them in implementing regenerative EWF system pilot projects; and Engage the private sector to promote market-based planning and investment to support pilot project implementation.

In this paper, we present findings on micro-concentrator photovoltaic cells composed of lattice matched subcells grown on GaAs and InP substrates, which are stacked into single, four-terminal devices using micro-transfer printing. The design, modeling, growth, fabrication and assembly of the devices will be described, and potential interconnection schemes to achieve efficient, two-terminal strings of cells with flexible current and voltage outputs and resilience to defects is discussed.

Micro-concentrator photovoltaics (μ-CPV) may provide a cost effective means of producing terrestrial solar power with high area efficiency. By printing CPV onto a transparent substrate, a Si back panel can be used to capture the diffuse sunlight component. Models show that efficiencies above 30% can be achieved even under global normal irradiance (GNI) with a 40% diffuse component. Additionally, the power output of existing installations can be boosted by adding a transparent μ-CPV array on top.To further the development of this technology, we have created a model to analyze μ-CPV array reliability under non-ideal conditions. The adverse effects of partial shading on standard large area panels such as crystalline Silicon (c-Si) are well known, but little investigation has been done on the tolerance of the μ-CPV components. In this article a SPICE simulation is used to analyze the effects of partial shading on a μ-CPV module and evaluate various circuit layouts.

Photoluminescence Excitation Spectroscopy (PLE) is a contactless characterization technique to quantify Shockley-Reed-Hall (SRH) lifetimes and recombination velocities in direct band gap experimental semiconductor materials and devices. It is also useful as to evaluate surface passivation and intermediate fabrication processes, since it can be implemented without the need for development of effective contact technologies. In this paper, we present a novel experimental PLE system for precision-based quantification of the aforementioned parameters as well as a system for which absolute PLE characterization may occur. Absolute PLE measurements can be used to directly calculate VOC for new photovoltaic (PV) material systems and devices. Key system capabilities include a continuous excitation spectrum from 300 nm -1.1 μm, automated characterization, up to 1 nm wavelength resolution (up to 60x higher than prior work), and a reduced ellipsometry requirement for post-processing of data. We utilize a GaAs double heterostructure (DH) and an InP crystalline wafer as calibration standards in comparison with data from an LED-based PLE to demonstrate the validity of the results obtained from this new system.

In this paper, we report findings from a micro CPV module, employing 170 μm GaAs-based 2J CPV cells, assembled on glass substrates using micro-transfer printing. The CPV array uses all-glass lens arrays to focus the light with a geometric concentration ratio of 740 suns, and a bifacial, monocrystalline silicon solar cell behind the substrate to capture the diffuse component of the light. We found that the diffuse capture creates a significant performance boost over CPV alone, and study the role of bifacial capture on the overall performance. The highest combined efficiency with respect to global normal irradiance was 25.4% for the module, measured by outdoor testing in Washington, DC.

One advantage of microconcentrator photovoltaics (mu-CPV) is the range of possible circuit connection arrangements. Large numbers of cells can be connected in combinations of series and parallel strings, which can provide a means to protect the module against performance loss due to cell failure, cell shading, and other variations in cell parameters that may arise during the fabrication and wiring processes. We introduce a model to evaluate the best strategy for optimizing module reliability through circuit layout using a combination of series and parallel connected cell strings. The model uses realistic solar cell device parameters in an electrical network simulation, coupled with a Monte Carlo method to introduce defects into the array with different probabilities. We use the model to optimize the layout of a mu-CPV panel designed to be integrated with the conventional 60-cell crystalline silicon panels for diffuse light capture to produce a hybrid direct/diffuse CPV product. (C) 2019 Society of Photo-Optical Instrumentation Engineers (SPIE)

GaAs is an attractive material for space solar cells due to it possessing the highest photovoltaic efficiency among semiconductors. However, material vulnerability to radiation damage is a limiting factor, which should be resolved. This can be done through the optimization of solar cell geometry. Specifically, ultra-thin GaAs solar cells possess increased radiation hardness in combination with high specific power (W/kg) making them desirable for space applications. In this research, modeling of single-junction thin GaAs based solar cells with an active device thickness <; 1.6 μm is performed to evaluate cell performance at high irradiation levels (1 MeV electrons with a fluence of 1E15 e - /cm 2 ) associated with high energy orbits. The radiation tolerance of two configurations is evaluated; conventional and rear junction (thick emitter) with a backside gold reflective coating. In addition, solar cell structures utilizing n- and p-type base are simulated. The Hovel model, modified to include the photon recycling effect, is used for modeling. The effect of radiation on GaAs electronic properties is counted through degradation of minority carrier lifetime and changes in the carrier concentration. It's found that conventional n-emitter/p-base and the rear junction with p-type thick emitter configurations with a heavily doped absorber ~5E18 [cm -3 ] and thickness below 800 nm have increased radiation hardness with a degradation rate <; 7%.

Mechanically stacked tandem solar cells are a potential near-term solution for increasing the efficiency of photovoltaic modules. Practical implementation requires an interconnection approach that maximizes efficiency and minimizes complexity and cost. Connecting the top and bottom cells in a voltage-matched configuration allows two-terminal modules to be fabricated without altering the cell design or processing methods. Here, we experimentally demonstrate two-terminal voltage-matched GaInP2/Si minimodules. The two-terminal minimodules performed just as well as four terminal configurations when voltage-matching requirements were met. The magnitude of the efficiency loss experienced by the voltage-matched minimodule when voltage-matched conditions were not met depends on whether the voltage was constrained by the GaInP2 or Si cells. Monte Carlo simulations also indicate that the two-terminal voltage-matched tandems respond to small cell-to-cell parameter variations in a similar manner as four terminal tandems. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)

In this paper we simulate a nanodisc reflector array that can enhance light trapping to overcome the limitations of low absorption in thin crystalline Si (c-Si). We performed a numerical simulation for a cell design with a thin c-Si absorber layer less than 20 μm thick. Our results show that a potential short circuit current increase of up to 22.9% is achievable, effectively doubling the optical path length compared to a planar metallic reflector.

We demonstrate a novel concept for III-V engineered substrate cost reduction that does not rely on chemical-mechanical polishing or low-throughput release layer etching. With the potential for significant reduction to III-V substrate cost, the details of this concept are provided, as well as a demonstration of III-V devices grown on a membrane removed from its source substrate and bonded to a non-native target handle. The GaAs solar cell on membrane one-sun and concentration AM1.5 efficiencies register 16.2% and 19.1%, respectively, prior to the application of anti-reflection coating. This is a discrepancy of 2% (one-sun) and 1.2% (concentration) absolute versus a nominally identical control GaAs device, indicating the capability for high performance at reduced cost.

The electron beam induced current (EBIC) mode of a scanning electron microscope (SEM) is a widely used technique for the quantitative assessment of minority carrier diffusion length and surface recombination. Point source (one-dimensional) and extended source (two-dimensional) analytical models are two widely used approaches to assess this information in geometry where the electron beam (e-beam) is parallel to the p-n junction. In this article, a two-dimensional (2D) analytical model is evaluated and compared with 2D finite element numerical simulations, where the electron beam-solid interaction is modeled using a Monte Carlo simulation coupled with a drift-diffusion solver. The simulations are computed for both low and high level injection conditions. The effect of an e-beam injection level on the shape of EBIC profiles is analyzed to evaluate limitations of the analytical models.

We examine thermally evaporated MoOx films as a full-area rear contact to crystalline p-type Si solar cells for efficient hole-selective contacts. Prior to front- and rear-metallization, the implied open-circuit voltage (iVoc) is evaluated to be 646 mV with implied fill factor (iFF) of 82.5% for the tunnel SiOx/MoOx rear contacted cell structure with the passivated emitter on the textured surface, showing it is possible to achieve an implied 1-sun efficiency of 20.8%. Numerical simulation reveals that the electron affinity (χ) of the MoOx material strongly influences the performance of the MoOx contacted p-Si cell. Simulated band diagrams show that the values in χ of the MoOx layer must be sufficiently high in order to lower junction recombination, indicating that the highest efficiency of 21.1% is achievable for a high χ of 5.6 eV of MoOx films and back surface recombination velocity of <100 cm/s at p-Si/MoOx.

In this work, we demonstrated an enhanced surface passivation of epitaxially grown boron-doped Si emitters by replacing thermal SiO2 as a passivation layer employed in a 15.9% efficient 21-mu m Si solar cell (88 cm(2)) on stainless steel with a remote-plasma atomic layer deposition (ALD) of an Al2O3 film. A thin Al2O3 film deposited by remote-plasma ALD was very effective at reducing the emitter saturation current density (J(0e)) of epitaxial p(+)-emitter to 16.2 fA/cm(2), compared to the J0e of 184.9 fA/cm(2) by thermal SiO2 films. This reduction in J(0e) enables an increase in an implied open-circuit voltage (iVoc) from 630 to 688mV. Quokka simulation shows that about a 1.1% absolute efficiency increase in the calculated baseline efficiency of a 15.1% of the ultrathin Si solar cell can be achievable by enhancing emitter surface passivation without changing the concentration in either the epi-emitter or epi-base. Finally, our results show that a high efficiency of 17.3% can be reached from the calculated baseline efficiency of 15.1% using the optimized conditions of an epitaxially grown emitter in combination with increasing the base doping concentration and improved base recombination lifetime. (C) 2017 The Japan Society of Applied Physics

Tunnel junctions with low differential resistance and high transparency have been grown by molecular beam epitaxy on GaSb substrates. The resulting devices have been characterized and analyzed using a combination of electrical measurements and modeling. These devices have importance to multi-junction solar cells grown on GaSb substrates. The structures contain an n-type InAs quantum well embedded in a GaSb p/n junction, exploiting the high tunnel probability at the broken gap interface between p-type GaSb and n-type InAs, whilst having a minimal impact on the transparency of the device.

We examine the potential to enhance cell performance using wide bandgap metal oxide films as full-area rear contacts to p-type crystalline Si (c-Si) solar cells. We aim to introduce a band offset through wide bandgap nickel oxide rather than introducing a band bending through transition metal oxides (e.g. MoO x , V 2 Ox, WO x ). Our numerical simulation shows it is possible to achieve one-sun efficiency of 21.6% with the open-circuit voltage (V oc ) of 652 mV, the short-circuit current density (J sc ) of 39.9 mA/cm2 and the fill factor (FF) of 82.5% when the back surface recombination velocities is 100 cm/s at p-Si/NiO x .

This work examines a tandem module design with GaInP2 mechanically stacked on top of crystalline Si, using a detailed photovoltaic (PV) system model to simulate four-terminal (4T) unconstrained and two-terminal voltage-matched (2T VM) parallel architectures. Module-level power electronics is proposed for the 2T VM module design to enhance its performance over the breadth of temperatures experienced by a typical PV installation. Annual, hourly simulations of various scenarios indicate that this design can reduce annual energy losses to similar to 0.5% relative to the 4T module configuration. Consideration is given to both performance and practical design for building or ground mount installations, emphasizing compatibility with existing standard Si modules. (c) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)

Mechanically-stacked tandem solar cells combining existing photovoltaic technologies present a straightforward path toward higher conversion efficiencies. Voltage-matched configurations have been proposed as a simplified approach for fabricating two terminal modules, but they are subject to performance losses compared to four terminal configurations if voltage-matching conditions are not met. Here, we demonstrate a two terminal voltage-matched GaInP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Si tandem with 23% efficiency. Through a combination of experimental measurement and simulation, we explore the impact of voltage and fill factor mismatches between the top and bottom sub-cell strings. Our results show that efficiency losses are minimized when voltage-mismatches are accommodated by designing the bottom strings to have a higher voltage. Fill factor mismatches due to differences in series resistance also lead to changes in the optimal ratio of the number of cells in the top and bottom sub-cell strings.

Simulations were performed with LT-SPICE TM to evaluate the limiting effects of cell size, perimeter recombination, and sheet resistance on the performance of a solar cell under 500 sun light concentration. A circuit model was generated using parameters extracted from a 3 junction InGaP/GaAs/InGaAsN device and simulated with various contact configurations. The results of the simulation were then used to determine the optimal cell size for a gridless cell and the conditions under which a gridless cell is more efficient than a cell with grid fingers.

A tunnel junction has been developed with an application to multijunction solar cells grown on GaSb and analyzed using a combination of electrical device measurements and modeling. The device employs an InAs quantum well embedded in a GaSb p/n junction, exploiting the high tunnel probability at the broken-gap interface between p-type GaSb and n-type InAs and having a minimal impact on the transparency of the device. The concept is extended to wider bandgap heterointerfaces using Al(0.)2Ga(0.8)Sb, achieving a differential resistance of 4.08 x 10(-4) Omega cm(2). (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)