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III-nitride materials have attracted wide interests for optoelectronic and electronic applications due to their unique and tunable semiconducting and optical properties. Aluminum nitride (AlN) exhibits an ultra-wide bandgap of 6.2eV and wide transparency window from ultraviolet to mid-infrared, making it a promising candidate as an anti-reflective coating (ARC) material on silicon for photovoltaic (PV) devices. In this work, ray tracing is utilized to investigate the optical properties of AlN ARC on 150$\mu$m-thick c-Si absorber. AlN with thicknesses of 60–90nm are studied and the effects towards light absorption (within 300–1200nm wavelength region) and short-circuit current density ($J_{\mathrm{\text{SC}}})$ of the solar cell are analyzed. In the ray tracing, planar c-Si absorber without an ARC is used as a reference. The reference condition exhibits weighted average reflection (WAR) of 39.8% within the 300–1200nm wavelength region with $J_{\mathrm{\text{SC}}}$ of 25.49mA/cm². AlN with 80nm is found to be the optimum ARC thickness, which leads to the enhanced broadband absorption with WAR of 19.7% within the spectral region. This thickness represents the highest $J_{\mathrm{\text{SC}}}$ achieved in this work (35.71mA/cm${}^2)$.

III-nitride materials have attracted wide interests for optoelectronic and electronic applications due to their unique and tuneable semiconducting and optical properties. Gallium nitride (GaN) exhibits wide bandgap of 3.42eV, high thermal and chemical stability, with a strong potential to act as an electron selective contact (i.e., emitter) in GaN/Si heterojunction solar cells. However, despite all the advantages, to date, there is no published research that has which utilized GaN as an emitter in the GaN/Si heterojunction solar cells. In this work, SCAPS-1D simulation is utilized to investigate the electrical properties of GaN emitter on 150$\mu$m-thick monocrystalline silicon (mono c-Si) absorber layer in GaN/Si heterojunction solar cell architecture. GaN emitter with the thickness of 30–120nm are studied and the effects toward open-circuit voltage ($V_{\mathrm{\text{OC}}}$), short-circuit current density ($J_{\mathrm{\text{SC}}})$, fill factor (FF), power conversion efficiency (PCE) and external quantum efficiency (EQE) of the solar cell are analyzed. The optimum thickness of the GaN emitter is found to be 60nm with $J_{\mathrm{\text{SC}}}$ of 37.53mA/cm², $V_{\mathrm{\text{OC}}}$ of 628.73mV and PCE of 19.43%. The findings show the potential of the GaN/Si heterojunction solar cell for the future of the PV industry, especially for applications in harsh and extreme conditions.

An inductorless power converter for low-power energy harvesting is presented. The power converter for energy harvesting is employed to maximize power extraction from energy sources. The power converter is based on a capacitive boost converter which is divided into two stages; a number of first-stage in parallel and shared-stage. The first-stage maximizes power extraction from the energy source while the shared-stage operates as a conventional charge pump. For not only low-power energy source but also high-power energy source, the maximum power extraction is targeted by the proposed converter. The extracted power from energy sources enhances by range from 117% to 161% over the conventional design. The output current of the proposed converter with three first-stages is improved by 183% over conventional converter. The peak efficiencies achieved with three and one first-stage are 53.3% and 38.5% for the proposed and the conventional converters, respectively. The peak end-to-end efficiency is enhanced by 198% as compared to the conventional converter. The proposed inductorless power converter has been implemented on a 0.13μm CMOS process.

The atomic structures of grain boundary (GB) and their effect on the performance of poly-Si thin film solar cell are studied by multi-scale simulations. First, the atomic structures of various GBs are calculated using molecular dynamics. Subsequently, the energy band diagram are obtained by ab-initio calculations. Then, finite difference method is performed to obtain solar cell performance. The results show that the Σ5 (twist) GB can greatly enhance the carriers recombination and results in small short-circuit current density (J_SC) and open-circuit voltage (V_OC). However, the Σ17 (twist and tilt) GBs have little influence on the cell performance. Also revealed in the simulations is that the GB near the p–n junction leads to very small J_SC and V_OC. When the distance between GB and p–n junction increases from about 1.10 μm to 3.65 μm, the conversion efficiency increases by about 29%. The thickness effect of solar cell containing the Σ5 (twist) GB on the cell performance is also studied. The results show that the conversion efficiency and J_SC increase rapidly as the thickness increases from about 5.2 μm to 40 μm. When the thickness ranges from about 40 μm to 70 μm, the efficiency and the J_SC both increase gradually and reach their own peak values at about 70 μm. When the thickness exceeds 70 μm, the efficiency and J_SC both decrease gradually. However, the V_OC keeps increasing with increase in thickness. The effects of GB on the carrier transport and recombination processes are discussed to understand the above results.

The deposition rate of μc-Si films was investigated for four excitation frequencies 30, 40, 60, 70 and 80 MHz with other deposition parameters fixed. Deposition rate increases with the increasing of excitation frequency, while Raman crystallinity behaves more complicated. With the optimization of deposition parameters, p-i-n solar cells at an initial efficiency of 5.41% were fabricated. With the increasing of plasma excitation frequency, the non-uniformity of these thin films increases. To better understand the cause of the non-uniformity of these films, a numerical simulation was carried out. The numerical results generally followed the experimental data. It turned out that the standing waves and the evanescent wave guide modes on the electrode surface played an important role. In order to achieve highly uniform thin films, a triode-electrode was employed together with a pulsed power source. We found that with a proper choice of pulse frequency and DC voltage applied to the mesh, non-uniformity is less than 8% for films deposited on 10×10 cm² substrates. Simulations were also applied to analyze the results.

We present a study of the photovoltaic effects of a graphene/n- Si Schottky junction solar cell. The graphene/Si solar cell was prepared by means of rapid chemical vapor deposition, while the graphene films were grown with a CH₄/Ar mixed gas under a constant flow at 950°C and then annealed at 1000°C. It was found that the junction between the graphene film and the n-Si structure played an important role in determining the device performance. An energy conversion efficiency of 2.1% was achieved under an optical illumination of 100 mW. The strong photovoltaic effects of the cell were due to device junction's ability to efficiently generate and separate electron–hole pairs.

A photoanode using dye-sensitized ZnO nanowire (NW) is a good candidate for low-cost, colorful, light-weight and flexible solar cell material. We have synthesized a ZnO NW anode and a ZnO nanowire–nanoparticle (NWNP) anode, in which ZnO nanoparticles (NPs) are decollated on the surface of NWs. Photo-induced electron transfer dynamics from the excited state of sensitizer dye (D149) to the conduction band of ZnO NW and ZnO NWNP was clarified using femtosecond transient absorption spectroscopy. The decay of the single excited state ($S_1$) of D149 was faster in ZnO NW than that of ZnO NWNP, indicating that NW is more suitable as an efficient electron acceptor.

We report the growth of Cu₂SnS₃ (CTS) thin films on F-doped SnO₂ (FTO) glass substrates at room-temperature by low-cost electrodeposition technique using an aqueous medium without the evolution of hydrogen. Electrolyte concentration and deposition potential were optimized under the limits of water hydrolysis. As-deposited films are post-annealed in the presence of the sulphur flakes to establish the stoichiometry. The annealed films were found to contain high phase purity and favorable optical properties to be useful for the photovoltaic applications. Optical data reveal that the CTS films have direct optical bandgap of 1.25 eV with an absorption coefficient of the order of 10⁴ cm${}^{-1}$. A photovoltaic cell architecture of Glass/FTO (back contact)/CTS/CdS/Al:ZnO/Al (front contact) exhibited an open circuit voltage of 28 mV, a short circuit current density of 8.4 $\mu$A/cm² and the fill factor of 25%. The absorber thickness optimization and the use of Mo-coated glass as a back contact improve the solar cell parameters. A further study in this aspect is under way.

Recent trends of photovoltaics account for the conversion efficiency limit making them more cost effective. To achieve this we have to leave the golden era of silicon cell and make a path towards III–V compound semiconductor groups to take advantages like bandgap engineering by alloying these compounds. In this work we have used a low bandgap GaSb material and designed a single junction (SJ) cell with a conversion efficiency of 32.98%. SILVACO ATLAS TCAD simulator has been used to simulate the proposed model using both Ray Tracing and Transfer Matrix Method (under 1 sun and 1000 sun of AM1.5G spectrum). A detailed analyses of photogeneration rate, spectral response, potential developed, external quantum efficiency (EQE), internal quantum efficiency (IQE), short-circuit current density (J${}_{\mathrm{\text{SC}}}$), open-circuit voltage (V${}_{\mathrm{\text{OC}}}$), fill factor (FF) and conversion efficiency ($\eta$) are discussed. The obtained results are compared with previously reported SJ solar cell reports.

In this study, indium tin oxide (ITO) was deposited onto sapphire and low resistive p-Si substrates using pulsed laser deposition (PLD) technique. The optical energy gap of ITO deposited on the sapphire substrate was 3.7 eV at room temperature. Photoluminescence (PL) of ITO shows an emission of broad peak at 524 nm. Photovoltaic (PV) characteristics of the n-ITO/p-Si heterojunction are examined and showed conversion efficiency $(\eta )$ of 1.8%. The open circuit voltage $(V_{\mathrm{\text{OC}}})$ for this cell was 0.49 V while the short circuit current density $(J_{\mathrm{\text{SC}}})$ was 17.4 mA/cm². The fill factor of this cell was 22%. The ideality factor of ITO/Si heterojunction is about 3.1. The barrier height ${\mathrm{\Phi }}_B$ of the heterojunction was determined from I–V characteristics and was 0.83 eV. The responsivity of the heterojunction was measured and the maximum value of responsivity was 0.5 A/W without bias voltage. The minority carrier lifetime of the solar was measured using open circuit voltage decay (OCVD) method and found to be 227 $\mu$s.

Solar cell development has been largely done by investigating how changes in the structural design of new materials will affect the cell’s performance. Although this process has been used for decades, it can sometimes be slow and expensive. Therefore, a new approach to solar cell development must be taken via simulations and modeling to enhance the cell performance. Simulations and modeling before actual fabrication have the added benefit of avoiding wastage of costly materials and time. This paper reviews the various types of solar cells and discusses the latest developments in the photovoltaic field. It also expounds how modeling solar cells before the developmental phase is beneficial with a focus on COMSOL Multiphysics describing how it is particularly advantageous.

In this paper, we report the comparative study of some parameters of II–VI ternary alloy ZnCdTe and II–VI–O dilute oxide ZnCdTeO. The purpose of this comparative study is to establish both the ternary and quaternary alloys as superior materials for optoelectronic and solar cell applications in which the quaternary materials show more superiority than the ternary material. In this purpose, we take the data from the experiments previously done and published in renowned journals and books. The parameters of these alloys are mainly being calculated using Vegard’s law and interpolation method of those collected data. It was certainly demonstrated that the incorporation of O atoms produces a high bandgap ($\mathrm{\Delta }{E}_g$) reduction in host ZnCdTe (Zn${}_{1-x}$Cd_xTe) in comparison to the bandgap reduction in host ZnTe material with Cd incorporation. The bandgap of ZnCdTeO (Zn${}_{1-x}$Cd_xTe${}_{1-y}$O_y) was found to be reduced to 1.1357 at $x=y=0.5$ and the spin–orbit splitting energy (${\mathrm{\Delta }}_{\mathrm{\text{SO}}}$) value of ZnCdTeO was calculated to be 1.175eV for Cd concentration of 0.5mole and O concentration of 0.1mole both of which showed excellent results with the prospect of optoelectronic and solar cell applications. The constant rise in the spin–orbit curve signifies a very less internal carrier recombination which decreases the leakage current and augments the efficiency of solar cell. The lattice constants and strain calculation values give very good results and confirm the stability of the materials. Besides, the calculated band offsets values show that for ZnCdTeO, there is higher bandgap reduction than that of ZnCdTe. Moreover, ZnCdTeO covers a wide range of wavelength in the visible region starting from violet region at 393nm upto red region at 601nm. Both ZnCdTe and ZnCdTeO are found to have excellent applications in optoelectronic and solar cell devices though quaternary ZnCdTeO proves much supremacy over ternary ZnCdTe in all aspects of the properties.

Hydrogenated amorphous carbon films (a-C:H) were deposited on p-type silicon (a-C:H/p-Si) and quartz substrates by excimer laser at room temperature using mixture ratios 1 to 9 and 3 to 7 of camphor to graphite by weight percentages. The presence of hydrogen in the a-C:H films has been confirmed by Fourier transform infrared spectroscopy (FTIR) measurements. The structure and optical properties of a-C:H films were respectively investigated by Raman scattering and UV-visible spectroscopy. The increase of sp³ sites in the a-C:H films has also been confirmed by the Raman spectra spectroscopy analysis. The increase of the optical band gap with higher camphor percentage in the target was believed to be due to the increase of the sp³ hybrid forms of carbon arising from camphor incorporation. The formation of a heterojunction between the a-C:H film and Si substrate was confirmed by current–voltage (I–V) measurement. The structure of a-C:H/p-Si cells deposited using mixture ratios 1 to 9 of camphor to graphite by weight percentages showed better photovoltaic characteristics with an open-circuit voltage of 400 mV and short-circuit current density of about 15 mA/cm² under AM 1.5 (100 mW/cm² at room temperature) illumination. The energy conversion efficiency and fill factor were found to be approximately 2.1% and 0.38, respectively. The carbon layer contributed to the energy conversion efficiency in the lower wavelength region has been proved by the quantum efficiency measurement.

The parameter electron filling factor can be taken as a scale for the electronic states in the intermediate band which should be de-localized and thus the unconfined electrons at the quantum dots. For three different value of electron filling factor, the sunlight concentration effect on the efficiency of a quantum dot solar cell is calculated. The maximum point of efficiency and optimum thickness of the cell obtained under three different sunlight concentrations. We show the importance of electron filling factor as a parameter to be more considered. This parameter can be controlled by the quantum dots size and distance between quantum dot layers in the active region. Analysis of above mentioned parameters suggest that to attain a maximum efficiency, the size of the quantum dots and the distance between the periodically arrayed dot layers have to be optimized. In addition, sunlight concentration is recommended as an effective approach to have high efficiency and low cost level solar cells.

The equivalent circuit of the p-i-n structure has been considered and developed for the quantum dot intermediate band solar cells where the nanoparticles are inserted in the active region of the diode. The admittance of the circuits are calculated consisting of frequency dependent capacitance and conductance. The presence of quantum dot layers in the active region of the diode increases the capacitance and conductance of the cell in lower frequencies. However, the number of QD cannot be increased and has an optimum.

The performance degradation of a hybrid solar cell is modelled considering the variation of depletion width over time. The p-i-n structure of a TiO₂/perovskite/HTL photovoltaic is investigated. Several different time-dependent approaches are compared and a new model is introduced based on the variation of defect density over time in depletion region. This phenomenon consequently manifests itself in the device degradation. Our approach leads to rather complicated time-dependent equation for the defect density which takes into account also the non-uniformity of electric field in the depletion region. The thickness of TiO₂ nano layer is taken 50 nm and perovskite layer is 330 nm. The nanoscale thickness of TiO₂ layer warrants the carrier transport through tunneling mechanism.

For the first time, an optical model is applied to superstrate configuration of CdS/CIGS thin film solar cells with graphene front/back contact (FC/BC) to simulate the loss in current density and efficiency. Graphene shows to be a great candidate to replace with the metallic BC transparent conductive oxides as the front electrode. Our model is based on the refractive index and extinction coefficient and takes into account the reflection and absorption in interfaces and layer’s thickness, respectively. CIGS cells with graphene as front electrode have a lower current density and efficiency than the one with graphene BC. However, the bifacial configuration shows a higher current density and efficiency, mostly because of a higher transmission rate. The interference effect was observed in simulation of transmission rate of hybrid cells representing that graphene can cause multiple reflection. We simulated the device parameters versus the ZnO layer’s thickness, which is essential for high quality interfaces. However, the simulation results are also consistent when CdS thickness is replaced with inorganic ZnO.

The anti-reflective (AR) structure greatly reduces the light reflection. When it is applied on solar cells, it enables more light to be absorbed by the cells, increasing the energy of the incident light and improving the light-to-electricity conversion efficiency. In this study, the optical properties of AR microstructures are investigated followed by the performance evaluation of solar cells. The AR microstructure is arrayed in a uniform and periodic fashion. When it is applied on PMMA, only 1.0% of the light is reflected away while 2.6% of the light is reflected on glass. The angular dependence performance is also improved with AR structure with 9.4% more light absorption, which can increase the effective energy generation duration for the solar cell. The AR structure is applied to amorphous silicon thin film solar cells by nano-imprinting technology. The solar cell with AR structure gained 8.63% more power compared to the conventional solar cells.

The submicron array was fabricated onto a cyclo olefin copolymer (COC) film by a hot embossing method. An amorphous silicon p-i-n junction and transparent conductive layers were then deposited onto it through a plasma enhanced chemical vapor deposition (PECVD) and magnetron sputtering. The efficiency of the fabricated COC-based solar cell was measured and the result demonstrated 18.6% increase of the solar cell efficiency when compared to the sample without array structure. The imprinted polymer solar cells with submicron array indeed increase their efficiency.

In this work, numerical calculations and simulation based on Transfer Matrix Method have been presented to investigate a model solar cell structure. New four-layered structure containing different types of semiconductor has been presented, analyzed and discussed. The average reflectance and average transmittance in the visible light are derived and plotted versus the operating wavelength at different physical parameters. The obtained results show that the proposed structure is a promising candidate to be used for designing future solar cell structures.