Nanowire Solar Cells Research Articles

Role of Hole-Selective Contact in Efficiency Improvement of ITO-Free InP/MoO3/ PEDOT:PSS Nanowire Solar Cells

The use of nanostructures over traditional bulk and thin-film solar cells (SCs) increases the efficiency per unit volume due to the coupled effects of intrinsic antireflection and strong excitation of resonance modes. The structural optimization of InP nanowires (NWs) provides a deep insight into the electrical and optical parameters of NWs influenced by structural morphology. Here, we propose a core–shell structure using n-InP NW as a core coated with PEDOT:PSS/MoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> shell. We simulated the resultant structure using the finite difference time domain (FDTD) and device modules of Lumerical to investigate its optical and electrical behavior. The optical simulation predicts that a hole-selective layer over InP core increases the absorption of incident photons. An optimized thickness of shell reduces the required core material without affecting the ideal current density, resulting in low manufacturing cost. For core doping of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\times10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> , surface recombination velocity (SRV) of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> cm/s, and minority carrier lifetime ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\tau_{p}$ </tex-math></inline-formula> ) of 40 ns, an efficiency of ~25% can be achieved. In this article, we have also compared the optical and electrical characteristics of uncoated, PEDOT:PSS/InP NW and ITO/InP NW and electron-selective oxide-coated InP NW with our proposed structure and found that our proposed structure PEDOT:PSS/p-MoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> / n-InP heterojunction NWSC exhibits better photovoltaic (PV) performance than the above-mentioned structures.

High-Performance Laterally Oriented Nanowire Solar Cells with Ag Gratings

A laterally oriented GaAs p-i-n nanowire solar cell with Ag gratings is proposed and studied via coupled three-dimensional optoelectronic simulations. The results show that the gratings significantly enhance the absorption of nanowire for both TM and TE polarized light due to the combined effect of grating diffraction, excitation of plasmon polaritons, and suppression of carrier recombination. At an optimal grating period, the absorption at 650–800 nm, which is an absorption trough for pure nanowire, is substantially enhanced, raising the conversion efficiency from 8.7% to 14.7%. Moreover, the gratings enhance the weak absorption at long wavelengths and extend the absorption cutoff wavelength for ultrathin nanowires, yielding a remarkable efficiency of 13.3% for the NW with a small diameter of 90 nm, 2.6 times that without gratings. This work may pave the way toward the development of ultrathin high-efficiency nanoscale solar cells.

Efficient inclined core-shell nanowire solar cells

In this paper, we have designed an efficient nanowire array to improve and increase the amount of light trapped in nanostructured photovoltaic devices. The proposed solar cell benefits from inclined core-shell nanowires. The two structures of inclined nanowires (INWs) and vertical core-shell nanowires (VCSNWs) have been compared with the proposed structure in terms of the light absorption. An optimized solar cell can be obtained by examining the effect of design factors such as core-shell material, the angle of inclination and the core diameter. The results show that the absorption, short circuit current and efficiency are improved in the proposed designs. While the current density of the vertical nanowire solar cell is 33.1 mA/cm2, by adding the core and the inclination, it has been improved to 40.97 mA/cm2 and after finding the best core diameter and inclination angle it raised to 42.93 mA/cm2. The proposed nanowire array design can improve the performance of any other solar cell designs based on nanowires.

Numerical analysis of InP based high efficiency radial junction nanowire solar cell

III-V nanowire (NW) solar cells (SCs) promise a comparable efficiency to that of their planar counterparts with additional advantage of reduced material consumption to cut the manufacturing cost. However, the disadvantage of low minority carrier lifetime due to the large surface-to-volume ratio of NWs degrades its photovoltaic performance to some extent. To overcome this issue, the structure of radial junction instead of axial junction for NWSCs has been used, but in experimental realization, defect density increases in the radial junction structure at the interface of core/shell, resulting in low performance. In this paper, we propose a high performance radial junction NWSC, consisting of p-InP NW coated by Ta 2 O 5 and ITO, and simulate it using Lumerical software. The results show that the use of ITO/Ta 2 O 5 shell over the InP NW as an electron selective contact enhances the absorption of incident photons, which in turn increases efficiency, also providing the condition that the InP required for core can be reduced without sacrificing the ideal current density, leading to a decrease in the fabrication cost. Besides, we investigate and compare the photovoltaic parameters of the structures of ITO/Ta 2 O 5 /p-InP NWSCs with circular and rectangular cross-section in terms of minority carrier life time, doping, and surface recombination velocity (SRV). It is found that circular and rectangular NWSCs with the same filling ratio possess almost the same optimized ideal photo-current such that for the carrier life time of 400 ps and the SRV of less than or equal to 10 4 cm/s at the interface of Ta 2 O 5 /InP, an efficiency as high as ~24.5% and ~25.6% can be achieved for circular and rectangular NWSCs, respectively. • Performance of cylindrical and rectangular InP NW studied using FDTD method. • Optimization of nanostructures is performed in terms of optical Jsc. • Oxide shell ITO/Ta 2 O 5 is used to enhance the absorption and J sc . • Influence of carrier lifetime, doping, and SRV on photovoltaic performance is investigated. • PCE of ~24.5% and ~25.6% is achieved with cylindrical and rectangular NW respectively.

Wafer-Scale Synthesis and Optical Characterization of InP Nanowire Arrays for Solar Cells.

Nanowire solar cells have the potential to reach the same efficiencies as the world-record III–V solar cells while using a fraction of the material. For solar energy harvesting, large-area nanowire solar cells have to be processed. In this work, we demonstrate the synthesis of epitaxial InP nanowire arrays on a 2 inch wafer. We define five array areas with different nanowire diameters on the same wafer. We use a photoluminescence mapper to characterize the sample optically and compare it to a homogeneously exposed reference wafer. Both steady-state and time-resolved photoluminescence maps are used to study the material’s quality. From a mapping of reflectance spectra, we simultaneously extract the diameter and length of the nanowires over the full wafer. The extracted knowledge of large-scale nanowire synthesis will be crucial for the upscaling of nanowire-based solar cells, and the demonstrated wafer-scale characterization methods will be central for quality control during manufacturing.

Easy-to-fabricate high efficiency silicon nanowires solar cell modified by CdTe and zinc tetraphenyl porphyrin nanostructures

Liquid junction solar cell (LJSC) with vertically silicon nanowires (SiNWs) as the primary photosensitizer, co-sensitized with luminescent and narrow gap CdTe nanoparticles, and cuboidal microstructures of zinc tetraphenyl porphyrin (ZnTPP) dye offers broad and intense visible light absorption that translates into a maximum power conversion efficiency (PCE) of 9.09%, when combined with a polymeric gel of a I2/I− redox couple as the hole transport material and a counter electrode (CE) of poly(3,4-ethyelenedioxythiophene) doped with imide ions (PEDOT-N(CF3SO2)2), under 1 sun irradiance. The p-type CdTe efficiently scavenges holes from SiNWs and simultaneously allows the passage of photoexcited electrons from ZnTPP to SiNWs via electrical conduction thus imparting an enhanced solar cell performance. Co-sensitization also supresses back electron transfer effectively, as is inferred from a ~68% enhancement in PCE compared to SiNWs alone. Optimization of the CE entailed the evaluation of the effect of dopant anion: imide versus dicyanamide in PEDOT, and revealed that the presence of macro-cracks in the polymer surface, a deeper work function, and a lower electrical conductance are the shortcomings of the dicyanamide doped PEDOT and reduce the overall PCE, compared to imide. This study brings out how by judicious choice of photoanode and CE components, efficient, stable and easy-to-assemble LJSCs can be developed.

GaAs/AlGaAs Nanowire Array Solar Cell Grown on Si with Ultrahigh Power-per-Weight Ratio

Here we demonstrate a more effective use of III–V photoconversion material to achieve an ultrahigh power-per-weight ratio from a solar cell utilizing an axial p-i-n junction GaAs/AlGaAs nanowire (NW) array grown by molecular beam epitaxy on a Si substrate. By analyzing single NW multicontact devices, we first show that an n-GaAs shell is self-formed radially outside the axial p- and i-core of the GaAs NW during n-core growth, which significantly deteriorates the rectification property of the NWs in the axial direction. When employing a selective-area ex situ etching process for the n-GaAs shell, a clear rectification of the axial NW p-i-n junction with a high on/off ratio was revealed. Such a controlled etching process of the self-formed n-GaAs shell was further introduced to fabricate axial p-i-n junction GaAs NW array solar cells. Employing this method, a GaAs NW array solar cell with only ∼1.3% areal coverage of the NWs shows a photoconversion efficiency of ∼7.7% under 1 Sun intensity (AM 1.5G), which is the highest achieved efficiency from any single junction GaAs NW solar cell grown on a Si substrate so far. This corresponds to a power-per-weight ratio of the active III–V photoconversion material as high as 560 W/g, showing great promise for high-efficiency and low-cost III–V NW solar cells and III–V NW/Si tandem solar cells.

Aggregation induced emission (AIE) materials based on diketopyrrolopyrrole chromophore for CdS nanowire solar cell applications

We designed and synthesized two diketopyrrolopyrrole (DPP) derivatives (DPP1 and DPP2) which are substituted with phenyl and thiophene moieties in between DPP core and merocyanine dyes, respectively. The introduction of thiophene ring subunit at core position endows DPP2 significantly alters the photophysical, electrochemical and aggregation induces enhanced emissive (AIEE) properties compared to those of DPP1. As a practical point of view, we successfully employed DPP1 and DPP2 as sensitizer on CdS nanowires for fabrication of dye sensitized solar cell (DSSCs). The DSSC based on DPP2 (0.268%) dye yielded higher power conversion efficiency (PCE) as compared to DPP1 (0.195%) under standard illumination of Sunlight (AM 1.5 G, 100 mW/cm2). The basis for this different behaviour has been discussed.

Highly Stable Interdigitated PbS Quantum Dot and ZnO Nanowire Solar Cells with an Automatically Embedded Electron-Blocking Layer

We have constructed heterojunction iodide ligand PbS quantum dot (QD) and ZnO nanowire (NW) solar cells. In these interdigitated structures, PbS QDs are well-embedded within ZnO NWs grown on a dense ZnO layer. A Au back contact is directly formed on the iodide ligand PbS QD surface layer. In the widely studied colloidal QD-based heterojunction solar cells, the PbS QD active layer is sandwiched between the hole-blocking layer (or electron-accepting layer) and the electron-blocking layer (EBL) (or hole-transport layer). In contrast, our solar cells contain no EBL except an additional thin PbS QD capping layer, which was deposited on the interdigitated layer to ensure the complete infiltration of the PbS QDs, and prevent shortening between the ZnO NWs and Au back contact. The interdigitated layer was constructed using a layer-by-layer dip-coating method to achieve sufficient infiltration of PbS QDs in the ZnO NWs. Owing to highly efficient charge separation in the interdigitated structure, our cell achieved a high external quantum efficiency in the visible and infrared regions, despite using only iodide ligand PbS QDs. Using cross-sectional Kelvin probe force microscopy, we confirmed that the PbS QD capping layer formed between the ZnO NW and Au back contact intrinsically functioned as an EBL. Consequently, the solar cells with ZnO NWs and iodide ligand PbS QDs maintained their performance after 500 days of storage in air without encapsulation. This stability performance surpasses most of the previously reported solar cells with PbS QDs. An encapsulated 1.0 cm2 solar cell maintained its power output for over 75 h under continuous one-sun illumination with no significant degradation. The proposed solar cell architecture with an automatically embedded EBL can realize highly efficient and stable colloidal QD-based solar cells. Moreover, the interdigitated architecture concept can be extended to various organic and inorganic hybrid solar cells.

Efficient Charge Separation Enabled by N-Doped Graphene Quantum Dots and PCDTBT for a High-Performance Silicon Nanowire Solar Cell

Light absorption by n-silicon nanowires (SiNWs) grown by a chemical etching method is augmented by tethering photoresponsive and highly luminescent nitrogen-doped graphene quantum dots (N-GQDs) and poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) to a SiNW array. The resultant N-GQDs@PCDTBT@SiNW photoanode affords a wide, continuous, and intense absorption band spanning from ∼350 to 1200 nm wavelength range, enabling maximum light uptake, with a work function of ∼4.74 eV, deep enough to not serve as a charge-trapping state. Under illumination, efficient charge separation in this ternary composite is ensured by the p-type semiconducting nature of N-GQDs with a shallow valence band (VB) that allows for rapid hole extraction from the VBs of SiNW and PCDTBT and their rapid relay to the bromide ions in the electrolyte. This is simultaneously accompanied by fast, excited electron injection from N-GQDs and PCDTBT to the SiNW via a cascade process, thus minimizing back electron transfer to the tribromide ions. When the N-GQDs@PCDTBT@SiNW photoanode is coupled with a highly electrocatalytic and electrically conductive multiwalled carbon nanotube (MWCNT)@C-fabric counter electrode and a bromine/bromide electrolyte, a power conversion efficiency of 13.18% is achieved for this liquid junction solar cell, which is significantly enhanced compared to that of the SiNW/HBr,Br2/C-fabric cell (4.37%). The roles of N-GQDs, PCDTBT, and MWCNTs are independently quantified to explain the observed solar cell performance.

Investigation the absorption efficiency of GaAs/InAs nanowire solar cells

In this work, the absorption efficiency (Qabs) of GaAs/InAs core-shell nanowires on Si (111) for normal incident light is investigated. Simulations show the influences of NW diameter on the Qabs of the structure. Using the finite-difference time-domain (FDTD) and Mie theory, the highest Qabs for NW solar cells were obtained at a core diameter of 220 nm and a shell thickness of 35 nm. Additionally, the wavelength-dependent external quantum efficiencies (EQEs) for NWs were investigated. Numerical simulation of current density-voltage (J-V) characteristics of nanowires under illuminated conditions was studied. Furthermore, the band structure for GaAs core-shell nanowires was calculated. Optimized geometric parameters are obtained through the simulations.

Photovoltaic performance improvement of GaAs1-xBix nanowire solar cells in terms of light trapping capability and efficiency

This paper investigates optoelectronic performance of nanowire (NW) solar cells using GaAs and its alloy GaAs1-xBix for three different mole fractions of Bi e.g., x = 0.01, 0.043, 0.078 using extensive numerical simulation in order to evaluate the potential of the alloy as a solar cell material. Finite-difference time-domain (FDTD) method is used to obtain the optimum geometric dimensions of the nanowire in order to achieve maximum photocurrent. GaAs0.922Bi0.078 NW solar cell of length 2-µm and optimized diameter D = 140 nm with filling ratio (FR) of 0.5, produces a maximum Jsc of 49.31 mA/cm2 which is 23% higher than its GaAs counterpart. Additionally, GaAsBi NW exhibits much higher absorption, and lower reflection as well as transmission coefficients for the incident optical irradiation, due largely to its bandgap bowing property owing to incorporation of Bi, as compared to GaAs NW. Furthermore, we present electric field distribution and optical generation rate profiles under the incident irradiation in NWs to obtain a better insight into the device physics. Various material and transport parameters of the novel alloy material required to carry out electrical simulation using Lumerical 3D charge transport simulator, are presented in detail, and the effect of SRH recombination lifetime on the electrical performance i. e., open circuit voltage Voc and power conversion efficiency (PCE) of the NW solar cells is studied. Our findings reveal that GaAs0.99Bi0.01 NW exhibits the maximum PCE of 34.34% found to be 6.425% larger than that of GaAs NW under AM 1.5G illumination.

Analysis of highly efficient quad-crescent-shaped Si nanowires solar cell.

Nanostructured semiconductor nanowires (NWs) present a smart solution for broadband absorption solar cells (SCs) with high efficiency and low-cost. In this paper, a novel design of quad crescent-shaped silicon NW SC is introduced and numerically studied. The suggested NW has quad crescent shapes which create a cavity between any adjacent NWs. Such a cavity will permit multiple light scattering with improved absorption. Additionally, new modes will be excited along the NWs, which are highly coupled with the incident light. Further, the surface reflection from the crescent NWs is decreased due to the reduced surface filling ratio. The finite difference time domain method is utilized to analyze the optical characteristics of the reported structure. The proposed NW offers short circuit current density (Jsc) of 27.8 mA/cm2 and ultimate efficiency (ηul) of 34% with an enhancement of 14% and volume reduction of 40% compared to the conventional NWs. The Jsc and ηul are improved to 35.8 mA/cm2 and 43.7% by adding a Si substrate and back reflector to the suggested crescent NWs.

From Crystalline to Low-cost Silicon-based Solar Cells: a Review

Renewable energy has become an auspicious alternative to fossil fuel resources due to its sustainability and renewability. In this respect, Photovoltaics (PV) technology is one of the essential technologies. Today, more than 90 % of the global PV market relies on crystalline silicon (c-Si)-based solar cells. This article reviews the dynamic field of Si-based solar cells from high-cost crystalline to low-cost cells and investigates how to preserve high possible efficiencies while decreasing the cost. First, we discuss the various types of c-Si solar cells with different device architectures and report recent developments. Next, thin-film solar cells with their recent advancements are given. Then, Si nanowires solar cells and their recent results are discussed. Finally, we present the most encouraging tendencies in achieving low-cost solar cells utilizing cheap materials like heavily doped silicon wafers.

Absorption improvement of a-Si/c-Si rectangular nanowire arrays in ultrathin solar cells

Optical absorption of rectangular a-Si/c-Si solar cells is investigated. Each nanowire consists of a thin layer of a-Si, which surrounded by c-Si layers. The proposed structure has a very simple geometry compared with other nanowire solar cells, while its absorption rate is comparable to very complex structures. Periodic, semiperiodic, and multiple rectangular nanowires are used to achieve broadband absorption. In order to maximize the short-circuit current density of the proposed nanowire solar cells, particle swarm optimization algorithm has been performed. Irregularities have been observed to be one of the ways of absorbing broadband.

Eco-Friendly AgBiS2 Nanocrystal/ZnO Nanowire Heterojunction Solar Cells with Enhanced Carrier Collection Efficiency.

AgBiS2 nanocrystals (NCs) are nontoxic, lead-free, and near-infrared absorbing materials. Eco-friendly solar cells were constructed using interdigitated layers of ZnO nanowires (NWs) and AgBiS2 NCs, with the aim of elongating the otherwise short carrier diffusion length of the AgBiS2 NC assembly. AgBiS2 NCs were uniformly infiltrated into the ZnO NW layers using a low-cost and easily scalable dip coating method. The resulting ZnO NW/AgBiS2 NC interdigitated structures provided efficient carrier pathways in constructed nanowire solar cells (NWSCs), composed of a transparent electrode/ZnO NW/AgBiS2 NC interdigitated layer/P3HT hole transport layer/Au. The photocurrent external quantum efficiency (EQE) in the visible to near-infrared regions was enhanced compared to those of the control solar cells made with ZnO/AgBiS2 tandem layered structures. The maximum EQE for the NWSCs reached 82% in the visible region, which is higher than the EQE values previously reported for solar cells fabricated with ZnO/AgBiS2 NCs. Air stability tests on unsealed NWSCs demonstrated that 90% or more of the initial power conversion efficiency was maintained even after 6 months.

Ultra High Vacuum Chemical Vapor Deposition Techniques for Economic Growth of Silicon Nanowires

Ultra High Vacuum Chemical Vapor Deposition (UHVCVD) reactor has been used to grow silicon nanowires via innovative economical approaches using chemical active materials as catalysts such as aluminum. Scanning Electron Microscopy has been used to study the success of the growth for further investigations and advanced applications such as solar cells. Solar manufacturers are looking for approaches to improve yield and cell efficiency and lower manufacturing costs overall. One of the main goals of this project is to tear down the various parameters involved in the current photovoltaic panels and improve it in one or more directions (properties, performance, costs). The current study is addressing the solar market with special concern of the efficiency goal. The mechanical flexibility of plastic materials is of high demands for all photovoltaic applications onto curved surfaces for architectural integration. Polycarbonate AND/OR poly methyl methacrylate encapsulation of photovoltaic modules and usage to fabricate advanced silicon nanowires solar cells can be emerging technologies delivering excellent performance and durability at a competitive cost. Although solar panels with glass protective facing still account for the majority of the installations of photovoltaic modules, however, it is expected that the adaptation of these new technologies will rapidly gain market share. The growth of silicon nanowires using chemical vapor deposition to fabricate advanced solar cells can be done via two innovative approaches. Alternative techniques for lithographic formation of the mask can provide advantages for low-cost processing, especially where a simple repeating pattern is required.

Experimental and Theoretical Comparable Study of Pure and Zinc Porphyrin Surface Modified ZnO Nanorod Arrays for Hybrid Solar Cell Applications

Experimental and theoretical study Porphyrin-grafted ZnO nanowire arrays were investigated for organic/inorganic hybrid solar cell applications. Two types of porphyrin – Tetra (4-carboxyphenyle) TCPP and meso-Tetraphenylporphine (Zinc-TPP)were used to modify the nanowire surfaces. The vertically aligned nanowires with porphyrin modifications were embedded in graphene-enriched poly (3-hexylthiophene) [G-P3HT] for p-n junction nanowire solar cells. Surface grafting of ZnO nanowires was found to improve the solar cell efficiency. There are different effect for the two types of porphyrin as results of Zn existing. Annealing effects on the solar cell performance were investigated by heating the devices up to 225 °C in air. It was found that the cell performance was significantly degraded after annealing. The degradation was attributed to the polymer structural change at high temperature as evidenced by electrochemical impedance spectroscopy measurements.

Nanowire Solar Cell Above the Radiative Limit

AbstractA lossless solar cell operating at the Shockley–Queisser limit generates an open circuit voltage (Voc) equal to the radiative limit. At Voc, the highly directional beam of photons from the sun is absorbed and subsequently externally re‐emitted into a 4π solid angle, providing a large photon entropy loss. A solar cell can beat the Shockley–Queisser limit and approach the 46.7% ultimate limit by decreasing the output solid angle of the light emission at open circuit conditions. Here, a design for an indium phosphide single nanowire solar cell capable to operate 159 mV above the radiative limit is presented. The spontaneous emission factor is first optimized into a guided mode of the nanowire toward 68%. The authors subsequently launch a guided mode at the bottom straight part of the tapered nanowire yielding a photon escape probability of 81% for a tapering angle of θ = 1.2° and a top facet with a radius of 83 nm. When assuming homogeneous light emission along the nanowire, an outcoupling efficiency of 42% of the emitted light is obtained. The final optimization is the reduction of the emission cone toward 11 × 10−3 sr by focusing the guided mode with an external lens.

Surface roughness effect on characteristics of Si nanowire solar cell

The characteristics of silicon nanowires (SiNWs) with surface roughness are reported and analyzed for solar cell (SC) applications. The SiNWs are fabricated using a metal-assisted chemical etching process. The effects of the etching time and reaction temperature on the surface roughness and the performance of the SiNWs are investigated. Further, the optical and electrical characteristics of the roughed NW SC are numerically studied and optimized using 3D finite difference time domain and finite element analysis, respectively. The numerically optimized SiNWs with surface roughness offer high optical ultimate efficiency (η) of 32.51% with an enhancement of 15.98% over the smoothed SiNW. This is due to the surface textures of the nanowires which produce multiple light scattering between the NWs’ walls. This will enhance the optical path length through the NW and enrich its light absorption. The doping level of the surface roughness of NWs with p-type/intrinsic/n-type (p-i-n) axial configurations is also simulated to compute the optoelectronic performance of the suggested design. The p-i-n axial doped design offers a power conversion efficiency of 14.92%, whereas the conventional NWs have a power conversion efficiency of 13.16%.