Enhanced Carrier Collection Research Articles

Achieving Over 10% Efficiency in Kesterite Solar Cells via Selenium-Free Annealing

The unsatisfactory crystalline quality of the absorber layer has seriously impeded the development of kesterite photovoltaic devices, including a small grain size, a typical multi-layer structure, and inherent defects and defect clusters. Herein, we simultaneously modify the nature of the absorber bulk and the heterojunction interface by sputtering quaternary alloy targets and subsequent selenium-free annealing to improve the photovoltaic performance of Cu2ZnSnSe4 (CZTSe) solar cells. By adjusting the sputtering power, the elemental content and distribution in the precursor film are effectively controlled, which helps to obtain a single-layer large grain CZTSe absorber layer with better homogenization and compactness. The harmful inherent defects are significantly suppressed by such a modification. Simultaneously, the widened depletion width and enhanced built-in electric field, as well as improved band alignment at the heterojunction, enhance carrier collection. As a consequence, the efficiency of CZTSe solar cells has improved greatly from 6.91% to 10.12%. The single-target preparation strategy without selenization provides a simple and novel perspective for simultaneously adjusting the morphology and defects of kesterite photovoltaic materials, paving the way for promoting innovative industrial applications.

Direct growth of graphene on hyper-doped silicon to enhance carrier transport for infrared photodetection

The importance of infrared photodetectors cannot be overstated, especially in fields such as security, communication, and military. While silicon-based infrared photodetectors are widely used due to the maturity of the semiconductor industry, their band gap of 1.12 eV limits their infrared light absorption above 1100 nm, making them less effective. To overcome this limitation, we report a novel infrared photodetector prepared by growing graphene on the surface of zinc hyper-doped silicon. This technique utilizes hyper-doping to introduce deep level assisted infrared light absorption benefit from the enhanced carrier collection capacity of graphene. Without introducing new energy consumption, the hyper-doped substrate annealing treatment is completed during the growth of graphene. By the improvement of transport and collection of charge carriers, the graphene growth adjusts the band structure to upgrade electrode contact, resulting in a response of 1.6 mA W−1 under laser irradiation with a wavelength of 1550 nm and a power of 2 mW. In comparison, the response of the photodetector without graphene was only 0.51 mA W−1, indicating a three-fold performance improvement. Additionally, the device has lower dark current and lower noise current, resulting in a noise equivalent power of 7.6 × 10–8 W Hz−0.5. Thus, the combination of transition metal hyper-doping and graphene growth technology has enormous potential for developing the next generation of infrared photodetectors.

Controllable Double Gradient Bandgap Strategy Enables High Efficiency Solution‐Processed Kesterite Solar Cells

AbstractThe double gradient bandgap absorber has the potential to enhance carrier collection, improve light collection efficiency, and make the performance of solar cells more competitive. However, achieving the double gradient bandgap structure is challenging due to the comparable diffusion rates of cations during high‐temperature selenization in kesterite Cu2ZnSn(S,Se)4 (CZTSSe) films. Here, it has successfully achieved a double gradient bandgap in the CZTSSe absorber by spin‐coating the K2S solution during the preparation process of the precursor film. The K2S insertion serves as an additional S source for the absorber, and the high‐affinity energy of K‐Se causes the position of the spin‐coated K2S solution locally Se‐rich and S‐poor. More importantly, the position of the bandgap minimum (notch) and the depth of the notch can be controlled by varying the concentration of K2S solution and its deposition stage, thereby avoiding the electronic potential barrier produced by an inadvertent notch position and depth. In addition, the K─Se liquid phase expedites the selenization process to the elimination of the fine grain layer. The champion CZTSSe device achieved an efficiency of 13.70%, indicating the potential of double gradient bandgap engineering for the future development of high‐efficiency kesterite solar cells.

Enhanced Carrier Collection in Cd/In-Based Dual Buffers in Kesterite Thin-Film Solar Cells from Nanoparticle Inks.

Increasing the power conversion efficiency (PCE) of kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cells has remained challenging over the past decade, in part due to open-circuit voltage (VOC)-limiting defect states at the absorber/buffer interface. Previously, we found that substituting the conventional CdS buffer layer with In2S3 in CZTSSe devices fabricated from nanoparticle inks produced an increase in the apparent doping density of the CZTSSe film and a higher built-in voltage arising from a more favorable energy-band alignment at the absorber/buffer interface. However, any associated gain in VOC was negated by the introduction of photoactive defects at the interface. This present study incorporates a hybrid Cd/In dual buffer in CZTSSe devices that demonstrate an average relative increase of 11.5% in PCE compared to CZTSSe devices with a standard CdS buffer. Current density-voltage analysis using a double-diode model revealed the presence of (i) a large recombination current in the quasi-neutral region (QNR) of the CZTSSe absorber in the standard CdS-based device, (ii) a large recombination current in the space-charge region (SCR) of the hybrid buffer CZTSSe-In2S3-CdS device, and (iii) reduced recombination currents in both the QNR and SCR of the CZTSSe-CdS-In2S3 device. This accounts for a notable 9.0% average increase in the short-circuit current density (JSC) observed in CZTSSe-CdS-In2S3 in comparison to the CdS-only CZTSSe solar cells. Energy-dispersive X-ray, secondary-ion mass spectroscopy, and grazing-incidence X-ray diffraction compositional analysis of the CZTSSe layer in the three types of kesterite solar cells suggest that there is diffusion of elemental In and Cd into the absorbers with a hybrid buffer. Enhanced Cd diffusion concomitant with a double postdeposition heat treatment of the hybrid buffer layers in the CZTSSe-CdS-In2S3 device increases carrier collection and extraction and boosts JSC. This is evidenced by electron-beam-induced current measurements, where higher current generation and collection near to the p-n junction is observed, accounting for the increase in JSC in this device. It is expected that optimization of the heat treatment of the hybrid buffer layers will lead to further improvements in the device performance.

Silver Alloying in Highly Efficient CuGaSe2Solar Cells with Different Buffer Layers

This study evaluates the effect of silver alloying, stoichiometry, and deposition temperature of wide‐gap (Ag,Cu)GaSe2(ACGS) absorber films for solar cell applications. Devices using a standard CdS buffer exhibit a strong anticorrelation between the open‐circuit voltage (VOC) and short‐circuit current density (JSC), withVOCdecreasing andJSCincreasing toward stoichiometric absorber composition. Increasing the ACGS deposition temperature leads to larger grains and improvedJSC, whileVOCis not affected. By adding more silver to the absorber (maximum tested [Ag]/([Ag]+[Cu]) [AAC] = 0.4), the widening of the space charge region (SCR) significantly enhances carrier collection. Experimental quantum efficiency spectra can be accurately simulated when assuming a very low diffusion length and perfect collection in the SCR. The highest efficiency of 8.3% (without antireflection coating [ARC]) is reached for an absorber with AAC = 0.4 grown at 600 °C. Replacing CdS by a (Zn,Sn)O buffer with lower electron affinity strongly mitigates interface recombination. Moreover, theVOC–JSCanticorrelation is not evident anymore and the highest efficiency of 11.2% (11.6% w/ARC,VOC = 985 mV,JSC = 18.6 mA cm−2, fill factor = 61.0%) is reached for a close‐stoichiometric ACGS solar cell with AAC = 0.4 processed at 650 °C.

Optically Resonant Bulk Heterojunction PbS Quantum Dot Solar Cell.

We design an optically resonant bulk heterojunction solar cell to study optoelectronic properties of nanostructured p–n junctions. The nanostructures yield strong light–matter interaction as well as distinct charge-carrier extraction behavior, which together improve the overall power conversion efficiency. We demonstrate high-resolution substrate conformal soft-imprint lithography technology in combination with state-of-the art ZnO nanoparticles to create a nanohole template in an electron transport layer. The nanoholes are infiltrated with PbS quantum dots (QDs) to form a nanopatterned depleted heterojunction. Optical simulations show that the absorption per unit volume in the cylindrical QD absorber layer is enhanced by 19.5% compared to a planar reference. This is achieved for a square array of QD nanopillars of 330 nm height and 320 nm diameter, with a pitch of 500 nm on top of a residual QD layer of 70 nm, surrounded by ZnO. Electronic simulations show that the patterning results in a current gain of 3.2 mA/cm2 and a slight gain in voltage, yielding an efficiency gain of 0.4%. Our simulations further show that the fill factor is highly sensitive to the patterned structure. This is explained by the electric field strength varying strongly across the patterned absorber. We outline a path toward further optimized optically resonant nanopattern geometries with enhanced carrier collection properties. We demonstrate a 0.74 mA/cm2 current gain for a patterned cell compared to a planar cell in experiments, owing to a much improved infrared response, as predicted by our simulations.

Nanocarbon ohmic electrodes fabricated by coaxial arc plasma deposition for phosphorus-doped diamond electronics application

n-Type (phosphorus-doped) diamond is a promising material for diamond-based electronic devices. However, realizing good ohmic contacts for phosphorus-doped diamonds limits their applications. Thus, the search for non-conventional ohmic contacts has become a hot topic for many researchers. In this work, nanocarbon ohmic electrodes with enhanced carrier collection efficiency were deposited by coaxial arc plasma deposition. The fabricated nanocarbon ohmic electrodes were extensively examined in terms of specific contact resistance and corrosion resistance. The circular transmission line model theory was used to estimate the charge collection efficiency of the nanocarbon ohmic electrodes in terms of specific contact resistance at a specific voltage range (5–10 V); they exhibited a specific contact resistance of 1 × 10−3 Ωcm2. The result revealed one order reduction in the specific contact resistance and, consequently, a potential drop at the diamond/electrode interface compared to the conventional Ti electrodes. Moreover, the fabricated nanocarbon electrodes exhibited high mechanical adhesion and chemical inertness over repeated acid treatments. In device applications, the nanocarbon electrodes were evaluated for Ni/n-type diamond Schottky diodes, and they exhibited nearly one order enhancement in the rectification ratio and a fast charge collection at lower biasing voltages.

Enhanced carrier collection efficiency of GeSn single quantum well towards all-group-IV photonics applications

GeSn-based quantum wells (QWs) are of great interests for the development of all-group-IV optoelectronic devices such as lasers. Using a GeSn buffer and SiGeSn barrier has been studied with the aim of obtaining a direct bandgap well and increasing the carrier confinement. However, the carrier collection efficiency with such a configuration remains unsatisfactory. In this work, a single QW with additional GeSn barrier inserted between the GeSn well and the SiGeSn barrier was grown and characterized. Under relatively low carrier injection, the photoluminescence results show dramatically enhanced emission from the QW compared to the reference samples with only SiGeSn barrier, indicating a significantly improved carrier collection efficiency of the well.

Room Temperature Electrodeposition of Ready-to-Use TiOx for Uniform p-n Heterojunction Over Nanoarchitecture.

The photocathodes are essential in photoelectrochemical systems for harvesting solar energy as green fuels. However, the light-absorbing p-type semiconductor in them usually suffers from carrier recombination issues. An effective strategy to address it is fabricating the p-n heterojunction to create an interfacial electric field. However, plenty of deposition process of the n-type layer for this purpose requires either sophisticated instruments or subsequent treatments, which may damage the vulnerable p-type structure. Herein, we report a mild approach for a ready-to-use n-type layer with full functionality. Structural analyses proved the successful coating of a uniform titania layer (up to 40 nm) over Cu2O without damaging its structure. Owing to the high Ti3+ content, the layer possesses excellent charge transport ability and requires no additional annealing. The heterojunction effectively facilitates the carrier separation and positively shifts the photocurrent onset potential for 0.2 V. The Mott–Schottky plot and the impedance study reveal an enhanced carrier collection with reduced charge transfer resistances. Such a nano-heterojunction can be further loaded with the hydrogen evolution catalyst, which almost doubles the photocurrent with an extended lifetime than that of the pristine Cu2O nanoarray. This approach puts forward a potentially scalable and efficient choice for fabricating photoelectrochemical devices.

Ge Solar Cells with Micro-Rod Arrays: Structural and Optical Properties.

Ge single-junction solar cell structures are grown on micro-patterned Ge substrates using lowpressure metalorganic chemical vapor deposition. 300 nm high micro-rod arrays are formed on the p-Ge substrates using photolithography and dry etching techniques. The micro-rod arrays are designed with rod diameter varying from 5 to 15 μm and arranged in a hexagonal geometry with rod spacing varying from 2 to 12 μm. Ge p-n junction structures are fabricated by phosphorus atomic diffusion process on the micro-patterned Ge substrates. 100 nm thick InGaP window and 300 nm thick GaAs cap layers are grown to reduce the surface recombination and the ohmic contact resistivity, respectively. Our results indicate that the micro-rod structures improve the performance of the Ge solar cells. An improvement of 16.1% in the photocurrent of the Ge micro-rod solar cell is observed compared to that of a reference Ge solar cell with planar surface. The improvement in the short circuit current density can be attributed to the light trapping effect, enlarged p-n junction area, and enhanced carrier collection efficiency. As a result, the conversion efficiency of the Ge solar cell with micro-rod arrays (5 μm diameter, 2 μm spacing, and 300 nm height) is improved from 3.84 to 4.78% under 1 sun AM 1.5G conditions.

Recent advances in the Van der Waals epitaxy growth of III‐V semiconductor nanowires on graphene

AbstractThe recent discovery of the one‐atom‐thick, two‐dimensional graphene layers with exciting properties including superb optical transparency and high mechanical robustness has stimulated extensive research interest for use as an alternative nanowires (NWs) growth platform for applications in next generation, flexible, stretchable, and printable electronic and optoelectronic devices. When combined with the exceptional capabilities of semiconductor NWs including improved light absorption, reduced optical reflectance, enhanced carrier collection, and fast response, the performance of optoelectronic devices could be significantly improved in novel high‐performance, flexible nanodevices. However, the growth of semiconductor NWs on 2D graphene layers is highly challenging owing to the absence of surface dangling bonds on graphene. Intriguingly, the last decade has witnessed a flurry of research activity on the growth of III‐V semiconductor NWs on graphene. In this review, we highlight the significant advancements that have been made in circumventing this challenge to realize the growth of III‐V semiconductor NWs on graphene. We then summarize the recent progress made in the development of graphene‐based NWs devices including photodetectors and solar cells. Finally, a brief conclusion and outlook of the way forward in the growth of semiconductor NWs on graphene is presented.

Effect of Surface Texture on Pinhole Formation in SiOx-Based Passivated Contacts for High-Performance Silicon Solar Cells.

High-efficiency silicon solar cells rely on some form of passivating contact structure to reduce recombination losses at the crystalline silicon surface and losses at the metal/Si contact interface. One such structure is polycrystalline silicon (poly-Si) on oxide, where heavily doped poly-Si is deposited on a SiOx layer grown directly on the crystalline silicon (c-Si) wafer. Depending on the thickness of the SiOx layer, the charge carriers can cross this layer by tunneling (<2 nm SiOx thickness) or by direct conduction through disruptions in the SiOx, often referred to as pinholes, in thicker SiOx layers (>2 nm). In this work, we study structures with tunneling- or pinhole-like SiOx contacts grown on pyramidally textured c-Si wafers and expose variations in the SiOx layer properties related to surface morphology using electron-beam-induced current (EBIC) imaging. Using EBIC, we identify and mark regions with potential pinholes in the SiOx layer. We further perform high-resolution transmission electron microscopy on the same areas, thus allowing us to directly correlate locally enhanced carrier collection with variations in the structure of the SiOx layer. Our results show that the pinholes in the SiOx layer preferentially form in different locations based on the annealing conditions used to form the device. With greater understanding of these processes and by controlling the surface texture geometry, there is potential to control the size and spatial distribution of oxide disruptions in silicon solar cells with poly-Si on oxide-type contacts; usually, this is a random phenomenon on polished or planar surfaces. Such control will enable us to consistently produce high-efficiency devices with low recombination currents and low junction resistances using this contact structure.

Opto-electrical characterization of quaternary sputtered copper indium gallium selenide nanorods via glancing angle deposition

Nanorod arrays have become an attractive alternative to their thin film and bulk counterparts in photovoltaic and photoconductivity research. This is mainly attributed to their superior optical and electrical properties. Light trapping and unique bandgap geometries in vertically aligned nanostructures result in high optical absorption and provide enhanced carrier collection by utilizing a fully depleted p-n junction between the anode and cathode via an isolated “capping” construction. The combination of these two features leads to the development of high efficiency nanostructured devices that can be utilized in solar cells and photodetectors. Optical absorption properties, geometry, and opto-electrical properties of nanorod arrays of CuInxGa(1−x)Se2 (CIGS), a p-type semiconductor with a wide bandgap ranging from 1.0 to 1.7 eV, are compared to their thin film counterparts. Utilizing a radio frequency sputtering system, a quaternary target, and glancing angle deposition technique, both isolated vertical arrays of CIGS nanorods and “core-shell” devices were fabricated, while conventional film devices were fabricated by normal incidence deposition. Scanning electron microscopy images indicated a successful growth of CIGS nanorods. Optical absorption and opto-electrical performance were found to be strongly improved by the presence of the isolated nanorod structures through spectroscopic reflectometry and responsivity testing under a solar simulator.

Electrical characterization of CIGS thin-film solar cells by two- and four-wire probe technique

A precise characterization of thin-film solar cells is of huge importance for obtaining high open-circuit voltage and low recombination rates from the interfaces or within the bulk of the main materials. Among many electrical characterization techniques, the two- and four-wire probe using the Cascade instrument is of interest since the resistance of the wires and the electrical contacts can be excluded by the additional two wires in four-wire probe configuration. In this paper, both two- and four-point probes configuration are employed to characterize the CIGS chalcogenide thin-film solar cells. The two-wire probe has been used to measure the current–voltage characteristics of the cell which results in a huge internal resistance. Therefore, the four-wire connection is also used to eliminate the load resistance to enhance the characterization’s accuracy. The load resistance in the two-wire probe diminishes the photogenerated current density at smaller voltage ranges. In contrast, the proposed four-wire probe collects more current at higher voltages due to enhanced carrier collection efficiency from contact electrodes. The current conduction mechanism is also identified at every voltage region represented by the value of the ideality factor of that voltage region. It is observed that a longer time given to the charge collection results in increased current density at a higher voltage. According to the results and device characteristics, a novel double-diode model is suggested to extract the saturation current density, shunt and series resistances and ideality factor of the cells. These cells are shown to be efficient in terms of low recombination at the interfaces and with lower series resistance as the quality of the materials is in its most possible conductive form. The measured internal resistance and saturation current density and ideality factor of the two measurement configurations are measured and compared.

Effect of post-MgCl2 activation on physical properties of e-beam evaporated CdTe films for absorber layer applications

In recent years, standard chloride activation process on CdTe absorber layer is a unanimously adopted by the thin film solar cell communities to improve the performance of concerned device because this activation process passivates the grain boundaries and enhances carrier collection. The toxic nature of CdCl2 emphasizes to find its alternative chlorine compound, and therefore in this communication, the impact of MgCl2 activation on microstructural and opto-electrical properties of thin CdTe films is explored. The structural analysis is carried out using X-ray diffractometer which revealed the augmentation in crystallite size (upto 320 °C) and polycrystalline nature and cubic phase with preferred orientation (111). The optical absorbance is undertaken employing UV–Vis spectrophotometer, and the absorbance in the visible region is found to be good for films activated at 320 °C. The morphological micrographs of films are taken by SEM technique, and the films showed granular like dense grains with the compact surface. The film deposition and chloride treatment are verified by EDS technique while the transverse current-voltage characteristics showed ohmic behavior. Based on results, the films processed at 320 °C could be utilized as effective absorber layer to fabricate high efficiency CdTe-based solar cells.

Investigations of the structural, optical properties and electronic structure of CdTe1−xSex films fabricated by RF magnetron sputtering

Se alloying CdTe absorber has attracted much attention for enhancing the short current density (Jsc) of CdTe device with high fill factor (FF) and open circuit voltage (Voc). The structural, morphological, optical properties and electronic structure of co-sputtered CdTe1−xSex films (0 ≤ x ≤ 1) are determined in this study. All CdTe1−xSex films are polycrystalline in nature. Phase transition occurs as x increases. The band gap (Eg) of CdTe1−xSex films can be tuned from 1.35 eV to 1.70 eV. CdTe and CdTe0.838Se0.162 films are p-type but the others are n-type, judging from the relative position of Fermi energy (EF) and the intrinsic Fermi energy (EI). Appropriate electric field can form in Se alloying CdTe absorber with a gradient composition, which enhances carrier collection. The barrier height at the emitter/absorber interface can be designed appropriately by changing the composition of CdTe1−xSex films. These results give reasons why CdTe1−xSex absorber is better than CdTe and device performance can be further improved by optimizing the composition distribution of CdTe1−xSex alloys.

The effect of excess selenium on the opto-electronic properties of Cu2ZnSnSe4 prepared from Cu-Sn alloy precursors.

For the fabrication of a kesterite-type CZTSe absorber material, stacked elemental-alloy layers (SEAL) precursor consisting of Cu–Sn alloy and elemental Zn layers offer the possibility of enhanced process control due to their advantages such as improvement of material homogeneity and suppression of the commonly observed Sn loss. In this study, the impact of selenium amounts during the annealing of a SEAL-type precursor with the configuration of Zn/Cu–Sn/Zn was demonstrated. The obtained results demonstrate how the selenium amount can indirectly be used to influence the absorber composition in the described annealing process and its direct impact on the opto-electronic properties of solar cells. This occurs due to the placement of elemental Sn in the vicinity of the sample during annealing that acts as a further source of SnSe2 vapor during the high-temperature stage of the process depending on the degree of selenium excess. The results show that higher selenium amount increases the band gap of kesterite; this is directly accompanied by a shift of the defect activation energies. Optimization of this effect can lead to widening of the space-charge width up to 400 nm, which improves the charge carrier collection. The described optimization strategy leads to device efficiencies above 11%.

Efficiency Improvement of Sb2Se3 Solar Cells via Grain Boundary Inversion

Sb2Se3 is a promising low-cost and low-toxicity photovoltaic material. Recent research revealed that recombination losses in the absorber limited the efficiency of Sb2Se3 solar cells. Herein we demonstrated a strategy of grain boundary (GB) inversion to alleviate such recombination loss. Owning to its one-dimensional crystal structure, we successfully inverted the GBs of Sb2Se3 films by introducing n-type Cu interstitial doping at GBs via low-temperature CuCl2 treatment. A built-in electric field is established between p-type grain interiors and n-type GBs, which spatially separates phototogerated carriers, suppresses recombination, and enhances carrier collection. Finally, we obtained an efficiency of 7.04%, which is the highest efficiency of Sb2Se3 solar cells based on rapid thermal evaporation technology. We envision that this GB inversion strategy is generally applicable to Sb2Se3 solar cells with different device configuration or produced from other methods and is extendable to other emerging low-dim...

Evidence of Enhanced Carrier Collection in Cu(In,Ga)Se2 Grain Boundaries: Correlation with Microstructure.

Solar cells containing a polycrystalline Cu(In,Ga)Se2 absorber outperform the ones containing a monocrystalline absorber, showing a record efficiency of 22.9%. However, the grain boundaries (GBs) are very often considered to be partly responsible for the enhanced recombination activity in the cell and thus cannot explain the registered record efficiency. Therefore, in the present work, we resolve this conundrum by performing correlative electron beam-induced current-electron backscatter diffraction investigations on more than 700 grain boundaries and demonstrating that 58% of the grain boundaries exhibit an enhanced carrier collection compared to the grain interior. Enhanced carrier collection thus indicates that GBs are beneficial for the device performance. Moreover, 27% of the grain boundaries are neutral and 15% are recombination-active. Correlation with microstructure shows that most of the ∑3 GBs are neutral, whereas the random high-angle grain boundaries are either beneficial or detrimental. Enhanced carrier collection observed for a big fraction of high-angle grain boundaries supports the "type-inversion" model and hence the downward band bending at GBs. The decrease in current collection observed at one of the high-angle grain boundaries is explained by Cu being enriched at this GB and hence by the upward shift of the valence band maximum.

Exploiting Polarization Charges for High-Performance (000-1) Facet GaN/InGaN/GaN Core/Shell/Shell Triangular Nanowire Solar Cell

In III–nitride nanowire (NW)-based solar cells, efficient utilization of polarization charges is essential in order to achieve high performance. In this paper, the polarization behavior of a GaN/In x Ga1– x N/GaN core/shell/shell triangular NW solar cell with {000-1} or {0001} as one of the facets is intensively studied through numerical simulations. An analysis of defect density, strain profile, and polarization charges at different facets of NWs with different “In” compositions is considered carefully. It is observed that an NW solar cell with a N-polar {000-1} facet is good enough to enhance carrier collection efficiency as compared with Ga-polar {0001} facet. This numerical study provides an innovative aspect of implementation of fundamental device physics with respect to recent growth techniques in order to realize the application of III–nitride NWs toward photovoltaic applications. The effect of an In x Ga1– x N layer with different “In” compositions in all crystallographic orientations of NW solar cells is also discussed. It is interesting to observe that a maximum conversion efficiency of ~3.85% with the 93.38% fill factor is achieved from an n-GaN/i-In x Ga1– x N/p-GaN nanowire solar cell considering 10% of “In” content under one Sun AM1.5 illumination.