InP Solar Cells Research Articles

Degradation assessment of a single junction InP solar cell under 1 MeV electron irradiation effect

Degradation assessment of a single junction InP solar cell under 1 MeV electron irradiation effect

InGaN based Schottky barrier solar cell: Study of the temperature dependence of electrical characteristics

The indium gallium nitride (InGaN) semiconductor alloy shows great promise for high-efficiency thin-film solar cells due to its intrinsic characteristics. However, there are major challenges in the development of high-quality p-doped and indium-rich InGaN layers to fabricate a pn or pin solar cell. This study focuses on the development of an alternative structure, not requiring p-doping, with a Schottky contact on n-type InGaN. The InGaN absorber was grown by metalorganic chemical vapor deposition and its structural, morphological and optical properties studied. Structural analysis by X-ray diffraction showed the growth of single crystal layers without phase separation. Indium compositions which vary up to around 8.3 % were confirmed by transmission measurements. The formation of V-shaped pits was observed with increased indium composition at lower growth temperatures. Schottky diodes based on InGaN with platinum metallic contacts were fabricated and their current–voltage characteristics studied in detail as a function of temperature. This analysis of the conduction mechanisms in Schottky/InGaN devices permitted in particular the extraction of the diode parameters as a function of the temperature showing a high rectification with an ideality factor of 1.15 with reverse saturation current of 6.7×10−9A at room temperature for an indium composition of 5.52 %. In addition, the analysis revealed the presence of a dual Gaussian distribution of barrier heights in a specific temperature range. Finally, the incident photon-to-electron conversion efficiency (IPCE) of the fabricated InGaN Schottky solar cells, measured using intensity-modulated photocurrent spectroscopy, reached a peak value of 51 %, which is among the highest published values for InGaN based solar cells.

Model development of lattice-matched p-GaInP/i-GaAs/n-GaInP hetero-junction solar cell and its performance optimization

We report an analytical model for our proposed lattice-matched hetero-junction p-GaInP/i-GaAs/n-GaInP solar cell with the incorporation of AlInP cap layer and MgF2/TiO2 anti-reflection region supported by numerical data obtained using SENTAURUS TCAD. We investigate the impact of intrinsic layer thickness, cap layer thickness, compositional variation of gallium in GaInP alloy used in p- and n-regions of pin solar cell and also studied the effect of indium tin oxide (ITO) anode contact on photovoltaic performance of solar cell in terms of performance matrices i.e., open circuit voltage (Voc), short circuit current density (Jsc), fill-factor and power conversion efficiency (PCE). Also the performance of the proposed solar cell is optimized by judiciously choosing intrinsic layer thickness, and cap layer thickness. Our proposed device featuring 2.1-μm thick i-layer, 156-nm thick cap layer with Ga0.5In0·5P/GaAs active region yields a PCE of 19.89% which turns out to be 67% improvement as compared to the conventional solar cell enabling the proposed design attractive for photovoltaic applications.

Electrically Detected Magnetic Resonance on a Chip (EDMRoC) for Analysis of Thin-Film Silicon Photovoltaics

Electrically detected magnetic resonance (EDMR) is a spectroscopic technique that provides information about the physical properties of materials through the detection of variations in conductivity induced by spin-dependent processes. EDMR has been widely applied to investigate thin-film semiconductor materials in which the presence of defects can induce the current limiting processes. Conventional EDMR measurements are performed on samples with a special geometry that allows the use of a typical electron paramagnetic resonance (EPR) resonator. For such measurements, it is of utmost importance that the geometry of the sample under assessment does not influence the results of the experiment. Here, we present a single-board EPR spectrometer using a chip-integrated, voltage-controlled oscillator (VCO) array as a planar microwave source, whose geometry optimally matches that of a standard EDMR sample, and which greatly facilitates electrical interfacing to the device under assessment. The probehead combined an ultrasensitive transimpedance amplifier (TIA) with a twelve-coil array, VCO-based, single-board EPR spectrometer to permit EDMR-on-a-Chip (EDMRoC) investigations. EDMRoC measurements were performed at room temperature on a thin-film hydrogenated amorphous silicon (a-Si:H) pin solar cell under dark and forward bias conditions, and the recombination current driven by the a-Si:H dangling bonds (db) was detected. These experiments serve as a proof of concept for a new generation of small and versatile spectrometers that allow in situ and operando EDMR experiments.

Efficient surface passivation of germanium nanostructures with 1% reflectance

Germanium (Ge) is a vital element for applications that operate in near-infrared wavelengths. Recent progress in developing nanostructured Ge surfaces has resulted in >99% absorption in a wide wavelength range (300–1700 nm), promising unprecedented performance for optoelectronic devices. However, excellent optics alone is not enough for most of the devices (e.g. PIN photodiodes and solar cells) but efficient surface passivation is also essential. In this work, we tackle this challenge by applying extensive surface and interface characterization including transmission electron microscopy and x-ray photoelectron spectroscopy, which reveals the limiting factors for surface recombination velocity (SRV) of the nanostructures. With the help of the obtained results, we develop a surface passivation scheme consisting of atomic-layer-deposited aluminum oxide and sequential chemical treatment. We achieve SRV as low as 30 cm s−1 combined with ∼1% reflectance all the way from ultraviolet to NIR. Finally, we discuss the impact of the achieved results on the performance of Ge-based optoelectronic applications, such as photodetectors and thermophotovoltaic cells.

Efficiency improvement of thin film solar cell using silver pyramids array and antireflective layer

In recent years, plasmonics has been widely employed to improve light trapping in solar cells. Silver nanospheres have been used in several research works to improve the capability of solar absorption. In this paper, we use silver pyramid-shaped nanoparticles, a noble plasmonic nanoparticle, inside thin-film silicon and InP solar cells to increase light absorption compared to previously published topologies. The proposed structure consists of a TiO2 pyramid structure placed at the top of the surface working as an anti-reflective layer, silicon/indium phosphate as an absorption layer, silver pyramid-shaped nanoparticles incorporated inside the absorption layer, and an aluminum reflecting layer at the bottom. In this research, we used finite difference time domain (FDTD) simulation to model the thin-film solar cell (TFSC). Optimizing the shape and placement of the silver pyramids, we have achieved an efficiency of 17.08% and 18.58% using silicon and InP as the absorbing layers respectively, which is significantly better than previously reported studies. The open-circuit voltages are 0.58 V and 0.92 V respectively, which is the highest among other configurations. To conclude, the findings of this study laid the foundation to create an efficient thin-film solar cell utilizing the light-trapping mechanism of noble plasmonic nanoparticles.

Unveiling the Role of H2Plasma for Efficient InP Solar Cells

III–V semiconductors are among the highest performing materials for solar energy conversion devices. Exposing III–V semiconductors to a hydrogen plasma can improve optoelectronic properties and is a critical step in fabricating efficient InP solar cells. However, there is a limited understanding of the changes induced by hydrogen plasma exposure to the surface and in the bulk of III–V semiconductors. Herein, it is demonstrated that a 19.3% efficient p‐InP solar cell with a TiO2electron selective contact layer can be achieved by exposing the InP substrate to hydrogen plasma. Detailed investigations employing ultraviolet photoelectron spectroscopy and capacitance–voltage measurement unveil that the hydrogen plasma exposure on p‐InP leads to charge carrier polarity inversion in the near‐surface region (charge inversion layer) while simultaneously reducing the carrier concentration (charge‐depleted layer) in the bulk. The study provides important insights into the impact of hydrogen plasma exposures on InP which may lead to more efficient optoelectronic devices such as solar cells, photodetectors, light‐emitting diodes, and photoelectrochemical cells.

Epitaxy and characterization of InP/InGaAs tandem solar cells grown by MOVPE on InP and Si substrates

The integration of III-V multi-junction solar cells on Si substrates is currently one of the most promising possibilities to combine high photovoltaic performance with a reduction of the manufacturing costs. In this work, we propose a prospective study for the realization of an InP/InGaAs tandem solar cell lattice-matched to InP on a commercially available Si template by direct MOVPE growth. The InP top cell and the InGaAs bottom cell were firstly separately grown and optimized using InP substrates, which exhibited conversion efficiencies of 13.5% and 11.4%, respectively. The two devices were then combined in a tandem device by introducing an intermediate InP/AlInAs lattice-matched tunnel junction, showing an efficiency of 18.4%. As an intermediate step towards the realization of the tandem device on Si, the InP and InGaAs single junction solar cells were grown on top of a commercial InP/GaP/Si template. This transitional stage enabled to isolate and evaluate the effects of the growth of III-V on Si on the photovoltaic performance through the comparison with the aforementioned devices on InP. Each cell was electrically characterized by external quantum efficiency and dark and illuminated current-voltage under solar simulator. The material quality was also analyzed by means of X-ray diffraction, Atomic-Force Microscopy, Transmission Electron and Scanning Electron Microscopy. The III-V on Si devices showed efficiencies of 3.6% and 2.0% for the InP and InGaAs solar cells, respectively.

Hydrodynamic and Energy Transport Model-Based Hot-Carrier Effect in GaAs pin Solar Cell

The hot-carrier effect and hot-carrier dynamics in GaAs solar cell device performance were investigated. Hot-carrier solar cells based on the conventional operation principle were simulated based on the detailed balance thermodynamic model and the hydrodynamic energy transportation model. A quasi-equivalence between these two models was demonstrated for the first time. In the simulation, a specially designed GaAs solar cell was used, and an increase in the open-circuit voltage was observed by increasing the hot-carrier energy relaxation time. A detailed analysis was presented regarding the spatial distribution of hot-carrier temperature and its interplay with the electric field and three hot-carrier recombination processes: Auger, Shockley–Read–Hall, and radiative recombinations.

A Modified Hexagonal Pyramidal InP nanowire Solar Cell structure for Efficiency Improvement: Geometrical Optimisation and Device Analysis

Vertically stacked nanostructure arrays are considered as promising candidates for photovoltaic (PV) applications. High absorption and excellent carrier collection efficiency along the axial direction with reductions inreflection and transmission losses have contributed significantly to increasing the efficiency of nanostructure-based InP solar cells (SCs). We investigated the optical and electrical behaviour of three distinct InP nanostructure geometries in this paper: hexagonal nanowire (HNW) SC, hexagonal nanopyramid (HNP) SC, and our proposed Hybrid hexagonal pyramidal nanowire (HHPNW) SC. The optimisation of the geometrical parameters of InP nanostructures grown on an InP substrate, such as diameter (D), period (p), and filling ratio (FR), offers a wide range of variations of the optical and device characteristics as a function of structural morphology. Finite Difference Time Domain (FDTD) simulation of HNW, HNP, and HHPNW structures reveals that our proposed HHPNW SC has a higher generation rate, better absorption, and higher optical short circuit current density (Jsc) of 34.2 mA/cm2 than the HNW (32.5 mA/cm2) and HNP (32.86 mA/cm2). The generation rate profile of all optimised nanostructures is transferred to Lumerical's Device Charge Solver module to investigate the electrical analysis in terms of PV parameters namely electrical Jsc, open-circuit voltage (Voc), Fill Factor (FF), and Power conversion efficiency (PCE). In the electrical analysis, we performed a comparative analysis of the p-n junction and p-i-n junction for all three structures under consideration, and it was observed that our proposed structure, InP HHPNW, outperforms the InP HNW and InP HNP with a conversion efficiency of 19.15 % and 23% for p-n and p-i-n junction, respectively.

Fabrication of a GaAs/GaNAsBi solar cell and its performance improvement by thermal annealing

To evaluate the performance of GaNAsBi alloys as solar cell materials, a GaNAsBi double-heterostructure pin solar cell was fabricated using plasma-assisted solid source molecular beam epitaxy. The addition of even a small amount of N (less than 1%) to the GaAsBi alloy significantly reduces the short-circuit current density (J sc) of the solar cell. However, after thermal annealing, J sc increases by ∼6.5 times. After thermal annealing, the GaN0.006As0.966Bi0.028 solar cells (bandgap (E g) = 1.15 eV) exhibited an open-circuit voltage (V oc) of 0.35 V, J sc of 10.2 mA cm−2, and fill factor of 0.56. Based on the Urbach energy of Ga(N)AsBi, the decreased crystallinity associated with the addition of N leads to poor characteristics of GaNAsBi solar cells compared with those GaAsBi solar cells.

Passivation of InP solar cells using large area hexagonal-BN layers

Surface passivation is crucial for many high-performance solid-state devices, especially solar cells. It has been proposed that 2D hexagonal boron nitride (hBN) films can provide near-ideal passivation due to their wide bandgap, lack of dangling bonds, high dielectric constant, and easy transferability to a range of substrates without disturbing their bulk properties. However, so far, the passivation of hBN has been studied for small areas, mainly because of its small sizes. Here, we report the passivation characteristics of wafer-scale, few monolayers thick, hBN grown by metalorganic chemical vapor deposition. Using a recently reported ITO/i-InP/p+-InP solar cell structure, we show a significant improvement in solar cell performance utilizing a few monolayers of hBN as the passivation layer. Interface defect density (at the hBN/i-InP) calculated using C–V measurement was 2 × 1012 eV−1cm−2 and was found comparable to several previously reported passivation layers. Thus, hBN may, in the future, be a possible candidate to achieve high-quality passivation. hBN-based passivation layers can mainly be useful in cases where the growth of lattice-matched passivation layers is complicated, as in the case of thin-film vapor–liquid–solid and close-spaced vapor transport-based III–V semiconductor growth techniques.

Bi-functional interfaces by poly(ionic liquid) treatment in efficient pin and nip perovskite solar cells

In this work, we demonstrate how the use of a poly(ionic liquid) interlayer in combination with perovskite solar cells provides a bi-functionality of the surface allowing to concomitantly reduce the energy losses, enhance the charge extraction and improve the device stability all at once.

Use of hetero intrinsic layer in GaAs P-I-N solar cell to improve the intermediate band performance

Intermediate band solar cell (IBSC) uses the below bandgap photons to minimise the spectral losses and to overcome the thermodynamical efficiency barrier for single junction solar cell set by Shockley and Queisser. With several practical constraints the IBSC is incapable to reach that thermodynamic barrier. Among them, increased recombination (both radiative and non-radiative) is a notable one, which significantly deteriorates the open-circuit voltage. In this paper a single junction GaAs PIN solar cell is proposed, where an InGaAs/GaAs hetero i-layer is introduced to the i-region. Inclusion of this i-layer reduces the transmission losses effectively by introducing an energy shift. This energy shift decouples the valence band form the intermediate band (IB), resulting an improvement in the carrier life time of electron hole pairs in the IB. As a result, the conversion efficiency increases significantly as compared to IBSC.

Modeling and simulation of high-efficiency GaAs PIN solar cells

A theoretical model for GaAs-based solar cells with PIN structure is proposed herein. The effect of varying key parameters on the conversion efficiency is investigated. The simulations are performed using COMSOL Multiphysics software. The mobilities of electrons and holes are varied in combination with the lifetime (LT). As a result, a maximum efficiency of 10.81% is achieved by setting the electron and hole mobility to 1.5k cm2 V−1 s−1 and 0.3k cm2 V−1 s−1, respectively. The electron and hole carrier LT are 3 ns and 7 ns, respectively, for the maximum output. The effect of the surface recombination velocity (SRV) is also studied, and a maximum efficiency of 13.75% is achieved for an SRV of 1k ms−1 for electrons and holes. The results show that higher photovoltaic efficiencies can be achieved by increasing the mobility and carrier LT while decreasing the surface recombination velocities.

Embossed Mie resonator arrays composed of compacted TiO2 nanoparticles for broadband anti-reflection in solar cells

Mie resonator arrays formed by embossing titanium dioxide (TiO2) nanoparticles (NPs) from solution are investigated as optical coatings for anti-reflection applications. Compacted nanoparticle assemblies offer unique possibilities to tailor the effective refractive index (RI). Here, we demonstrate a simple table-top, low pressure, and low temperature method to fabricate structured optical coatings. TiO2 nanostructures in the form of nanodisks support Mie resonances in the visible wavelength spectrum and exhibit strong forward scattering into the high index substrates, making them suitable as broadband anti-reflection coatings for solar cells. TiO2 NP-based nanodisk arrays are designed, fabricated, and characterized regarding their anti-reflection properties on Si, GaAs, and InP substrates and solar cells. Detailed finite-difference time-domain simulations are performed to optimize the TiO2 NP-based Mie resonator arrays for the broadband anti-reflection as well as to explain the measured reflectance spectra. The solar-weighted reflectance is used as a figure of merit (FoM). TiO2 nanodisk arrays on Si show a FoM of ~ 7% in the 400–1,100 nm wavelength spectrum; similar values are obtained for GaAs and InP substrates. TiO2 nanodisk arrays embossed directly on prefabricated planar single-junction Si, GaAs, and InP solar cells result in an appreciable increase (~ 1.3 times) in the short-circuit current densities.

Optical and electrical optimization of all-perovskite pin type junction tandem solar cells

A definitive breakthrough of perovskite solar cells towards large scale industrialization is believed to be the demonstration of higher efficiencies than conventional silicon technology, suggesting the exploration of perovskite tandem cell configurations. Since high efficiency tandem solar cells require careful optimization of photoactive as well as contact and additional functional layers, we propose an optical-electrical model to obtain the optimum layer thicknesses and the attainable electrical output parameters of two-terminal perovskite-perovskite tandem solar cells. The optical model takes into account the coherent propagation of light through the layer stack comprising two perovskite semiconductors and the corresponding contact layers, while the electrical model assumes two series-connected analytical current/voltage equations for pin solar cells. This model allows to assess the impact of the main physical parameters on each perovskite layer without requiring the high specificity needed in more rigorous numerical simulations. Efficiencies above 34% are predicted considering available perovskites with non-optimum bandgap and contact materials already proven in efficient laboratory solar cells. The requisite to attain such efficiencies is that recombination at the interfaces between the perovskite and contact materials is kept low in both bottom and top cells. Furthermore, within the assumption of non-optimum bandgaps of currently available perovskites, the simulation results suggest that efficiencies around 37% are possible when adopting contact materials with smaller absorption, more adequate refraction indices, and lower resistivity.

Nanoparticles-decorated silicon absorber: Absorption depth profile characteristics within absorbing layer

Here in this work, we carried out a simple and hand-on experiment to fabricate silver (Ag) nanoparticles on substrate (either Zinc oxide (ZnO) or p-Silicon (Si)) that could be used as base layer for thin film solar design in substrate and superstrate configurations. As-fabricated Ag nanoparticles were found to be ca. 100 nm on average and of wide range of interparticle gap distribution. Based on experimental observations, a typical model, “Ag nanoparticles array on c-Si” has been simulated in finite deference time domain (FDTD) analysis to understand the inherent optical characteristic such as absorption depth profile within Si layer. Model parameters such as solar incident wavelengths (450 nm, 650 nm and 1100 nm) and interparticle gaps (0, 1 and 3 nm) were varied and corresponding characteristics were analyzed. At 450 nm incident wavelength, absorption was localized at the interstitials as usual and propagated distribution within Si layer was observed for interacting nanoparticles array. In such case nearly half of the volume of Si absorbing layer got higher absorption distribution. At 650 nm incident wavelength, such absorption distribution within Si layer was found wide spread compared to those observed at 450 nm and 1100 nm incident wavelengths. Considering the fabrication process and predicted absorption profile in FDTD, a possible route to substrate and superstrate configuration of Si-based PIN solar cell was proposed. Such correlated investigations would facilitate in depth understanding as well as the development of emerging process needed to advance highly efficient design in photovoltaic technologies particularly plasmonic solar cells.

Performance Enhancement of Ultra-Thin Nanowire Array Solar Cells by Bottom Reflectivity Engineering.

A bottom-reflectivity-enhanced ultra-thin nanowire array solar cell is proposed and studied by 3D optoelectronic simulations. By inserting a small-index MgF2 layer between the polymer and substrate, the absorption is significantly improved over a broad wavelength range due to the strong reabsorption of light reflected at the polymer/MgF2 interface. With a 5 nm-thick MgF2 layer, the GaAs nanowire array solar cell with a height of 0.4–1 μm yields a remarkable conversion efficiency ranging from 14% to 15.6%, significantly higher than conventional structures with a much larger height. Moreover, by inserting the MgF2 layer between the substrate and a part of the nanowire, in addition to between the substrate and polymer, the absorption of substrate right below the nanowire is further suppressed, leading to an optimal efficiency of 15.9%, 18%, and 5.4% for 1 μm-high GaAs, InP, and Si nanowire solar cells, respectively. This work provides a simple and universal way to achieve low-cost high-performance nanoscale solar cells.

Effect of solar cell structure on the radiation resistance of an InP solar cell

Effect of solar cell structure on the radiation resistance of an InP solar cell