Theoretical study on InxGa1−xN/GaN quantum dots solar cell

In this work, the structure of In_xGa_1−xN/GaN quantum dots solar cell is investigated by solving the Schrödinger equation in light of the Kronig-Penney model. Compared to p-n homojunction and heterojunction solar cells, the In_xGa_1−xN/GaN quantum dots intermediate band solar cell manifests much larger power conversion efficiency. Furthermore, the power conversion efficiency of quantum dot intermediate band solar cell strongly depends on the size, interdot distance and gallium content of the quantum dot arrays. Particularly, power conversion efficiency is preferable with the location of intermediate band in the middle of the potential well.     

Simulation of IPV effect in In-doped c-Si with optimized indium concentration and layer thickness

Impurity photovoltaic effect(IPV) is one of the attempts to improve efficiency of solar cells and is the idea of exploiting three step generation via impurity states within the band gap to utilize sub-band gap photons. The three transitions are of electrons from valence band (VB) to conduction band (CB), valence band to impurity level and impurity level to conduction band. In the present simulation, we have used the p⁺nn⁺ structure in order to achieve higher photogenerated current and efficiency without loosing the open circuit voltage. Compared to other group-III elements in silicon solar cell, Indium is the most suitable material to achieve higher benefit in IPV. In this simulation, the model of IPV is considered to achieve the maximum benefit from the impurity state in a solar cell. To simulate we have used the one dimensional simulation program, SCAPS-1D. Again light trapping is an important part of IPV solar cell that has been considered in this simulation. Using IPV we have numerically demonstrated, an increase in efficiency, by 2.79% over that without-IPV effect and a 3.23% increase over the efficiency, 30.9% as reported by Schmeits and Mani [1].     

Detailed balance limit efficiency of silicon intermediate band solar cells

The detailed balance method is used to study the potential of the intermediate band solar cell (IBSC), which can improve the efficiency of the Si-based solar cell with a bandgap between 1.1 eV to 1.7 eV. It shows that a crystalline silicon solar cell with an intermediate band located at 0.36 eV below the conduction band or above the valence band can reach a limiting efficiency of 54% at the maximum light concentration, improving greatly than 40.7% of the Shockley—Queisser limit for the single junction Si solar cell. The simulation also shows that the limiting efficiency of the silicon-based solar cell increases as the bandgap increases from 1.1 eV to 1.7 eV, and the amorphous Si solar cell with a bandgap of 1.7 eV exhibits a radiative limiting efficiency of 62.47%, having a better potential.     

Control of simultaneous effects of the temperature,indium composition and the impact ionization process on the performance of the InN/InxGa1-xN quantum dot solar cells

The impact ionization in semiconductor materials is a process that produces multiple charge carrier pairs from a single excitation. This mechanism constitutes a possible road to increase the efficiency of the p-n and p-i-n solar cells junctions. Our study considers the structure of InN/InGaN quantum dot solar cell in the calculation. In this work, we study the effect of indium concentration and temperature on the coefficient $\theta$ of the material type parameter of the impact ionization process for a p(InGaN)-n(InGaN) and p(InGaN)-i(QDs-InN)-n(InGaN) solar cell. Next, we investigate the effect of perturbation such as temperature and indium composition on conventional solar cell’s (p(InGaN)-n(InGaN)) and solar cells of the third generation with quantum dot intermediate band IBSC (p(InGaN-i(QD-InN)-n(InGaN)) by analyzing their behaviour in terms of efficiency of energy conversion at the presence of the impact ionization process. Our numerical results show that the efficiency is strongly influenced by all of these parameters. It is also demonstrated that $\theta$ decreased with the increase of indium concentration and temperature which contributes to an overall improvement of the conversion efficiency.     

Correlation of band electronic structure with efficiency in perovskite solar cells with vanadium (Ⅳ) oxide thin film buffers

Perovskite solar cells have been studied extensively in the area of perovskite solar cells because they have a comparatively free hysteresis. Through fabrication of a perovskite solar cell based on a vanadium oxide buffer, this study clarified the mechanism of electron and hole transport in the laminated layer upon irradiation with light. The power conversion efficiency (PCE) of the Vanadium (Ⅳ) oxide (VO₂) sputtering process device was approximately 13% and with the spin-coating process was 8.5%. To investigate the physicochemical origin of such PCE differences depending on the process type, comprehensive band alignment and band structure analyses of the actual cell stacks were performed using X-ray photoelectron spectroscopy depth measurements. Accordingly, it was found that the inconsistent valence band offset between the perovskite absorption layer and V₂O₅ layer as a function of the VO₂ process type caused a difference in the hole transport, resulting in the difference in the efficiency.     

Control of the input efficiency of photons into solar cells with plasmonic nanoparticles

We study numerically the photon input efficiency of silicon solar cells due to gold plasmonic nanoparticles deposited on the cells. At low densities, when collective effects in light scattering by the nanoparticle ensemble are negligible, the absorption dependence increases linearly for a significant range of the solar spectrum. Collective effects lead to the input efficiency saturates, reaches its maximum and then decreases with nanoparticle density. The maximal input efficiency depends on the photon wavelength, nanoparticle shape and size, their distance to the cell, and the cell thickness, and can reach ~ 95% in thick solar cells. Finally, we show that aluminum nanoparticles improve the input efficiency in comparison with gold nanoparticles.     

Photovoltaic quantum efficiency enhancement by light harvesting of organo-lanthanide complexes

An increase of about 1% of the delivered power by a mono-crystalline commercial silicon solar cell has been obtained by coating the cell with an active poly-vinylacetate film doped with a light harvesting phenanthroline-Eu³⁺ complex. The dopant absorbs the UV component of the solar spectrum, where the silicon-based cells are almost blind, and emits red light that can be converted with an efficiency close to the maximum. This effect, achieved by a low cost encapsulation process, has been proven for the case of Air Mass 0 lighting conditions, and could be exploited also for terrestrial applications with the proper choice of the organic ligand.     

Impurity photovoltaic effect in silicon solar cell doped with sulphur: A numerical simulation

The impurity photovoltaic effect (IPV) has mostly been studied in various semiconductors such as silicon, silicon carbide and GaAs in order to increase infrared absorption and hence cell efficiency. In this work, sulphur is used as the IPV effect impurity incorporated in silicon solar cells. For our simulation we use the numerical device simulator (SCAPS). We calculate the solar cell performances (short circuit current density J_sc, open circuit voltage V_oc, conversion efficiency η and quantum efficiency QE). We study the influence of light trapping and certain impurity parameters like impurity concentration and position in the gap on the solar cell performances. Simulation results for IPV effect on silicon doped with sulphur show an improvement of the short circuit current and the efficiency for sulphur energy levels located far from the middle of the band gap especially at E_c-E_t=0.18 eV.     

Survey of intermediate band material candidates

A systematic ab initio study, using the local spin density approximation, of the electronic properties of Ga_xP_yM compounds, where M is a transition metal substituting Ga or P atoms in a GaP host semiconductor lattice is presented. This study is oriented towards the early identification of intermediate band materials of recent interest as new photovoltaic materials to exceed the efficiency of single gap and even tandems of two solar cells. M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn have been explored as transition metals and Sc, V, Cr, and Fe in Ga₃₂P₃₁M and Cr in Ga₃₁P₃₂M have exhibited the desired intermediate band.     

Computational analysis of the effect of the surface defect layer (SDL) properties on Cu(In,Ga)Se2-based solar cell performances

In this article, the performances of Cu(In,Ga)Se₂ (CIGS) solar cells have been modelled and numerically simulated using the one-dimensional simulation program Solar Cell Capacitance Simulator in 1 Dimension (SCAPS-1D), and a detailed analysis of the effect of surface defect layer (SDL) thickness, band gap and carrier mobility with Fermi level pinning is presented. Furthermore, donor-type defect state density in the SDL has been investigated, and their effect on device performances has been presented. Based on the simulation results, optimal properties of the SDL for the CIGS solar cell are proposed. The simulated results show that the optimal thickness of the SDL to optimise the solar cells is in the range of 100–200 nm. The increase in the band gap of the SDL >1.3 eV improves the device performance by enhancing the open-circuit voltage (V_oc), fill factor (FF) and conversion efficiency due to the larger quasi-Fermi energy-level splitting, and optimal band offset between the SDL and the buffer layer (CdS). The simulation results suggest that the SDL defect density as well as carrier mobilities are the critical parameters for the limitation of the performances for the CIGS solar cells. All these results show that the SDL plays an important role in designing high-efficiency and high-performance CIGS-based solar cells.     

Highly effective III-V solar cells by controlling the surface roughnesses

An advanced approach to minimize the light loss was discussed for III-V solar cells, by controlling the roughnesses of the device surface. Adhesives with different viscosities were applied to bond the III-V solar cells with the supporting substrate before the epitaxial lift-off process. The surface roughness of the III-V solar cells with epoxy adhesive (R_rms = 15.4 nm) is one order of magnitude higher than that with acrylic adhesive (R_rms = 1.6 nm), due to the differences in viscosity, resulting from the spreadability while being hardened. This roughness has increased the reflectance in the wavelength between 650 and 900 nm, implying that this reflectance is influenced by the rear surface of the solar cell. The device performance of the double-junction solar cells (Ga_0.5In_0.5P- and GaAs- based) also reflects the effect of the reflectance. The solar cell with the epoxy adhesive exhibited ~2% increase of the conversion efficiency than that with the acrylic adhesive, mainly due to the increased current density. The integrated current density from the external quantum efficiency (EQE) also exhibited ~2% increase only in the bottom (GaAs-based) cell, corresponding to the higher reflectance for red and near-infrared wavelength ranges.     

Enhanced photovoltaic performance of solution-processed Sb2Se3 thin film solar cells by optimizing device structure

Thin-film solar cells have attracted worldwide attention due to their high efficiency and low cost. Antimony selenide (Sb₂Se₃) is a promising light absorption material candidate for thin-film solar cells due to its suitable band gap, abundance, low toxicity, and high chemical stability. Herein, we fabricate an Sb₂Se₃ thin film solar cell using a simple hydrazine solution process. By controlling the thickness of the photoactive layer and inserting a poly(3-hexylthiophene) hole-transporting layer, an Sb₂Se₃ solar cell with a power conversion efficiency of 2.45% was achieved.     

Extending absorption of near-infrared wavelength range for high efficiency CIGS solar cell via adjusting energy band

The efficient photon harvesting in near infrared wavelength range is still a challenging problem for high performance Cu(In_1-x, Ga_x)Se₂ (CIGS) solar cell. Herein, adjusting the energy band distribution of CIGS solar cell could provide significant academic guidance for devices with superior output electric power. To understand the role of each functional layer, the optimal 3000 nm CIGS absorber layer with 1.3 eV bandgap and 30 nm CdS buffer layer were firstly obtained via simulating the uniform band-gap structures. By introducing CIGS absorber layer with a double grading Ga/(Ga+In) profile, the power conversion efficiency of the double gradient band gap cell is superior to that of uniform band-gap cell through extending absorption of near-infrared wavelength range. Upon optimization, the best power conversion efficiency of CIGS with a double gradient band gap solar cell is improved significantly to 24.90%, among the best values reported in literatures, which is an 8.17% relative increase compared with that of the uniform band-gap cell. Our findings provide a theoretical guide toward the design of high performance solar cells and enrich the understandings of the energy band engineering for developing of novel semiconductor devices.     

钙钛矿电池纳米陷光结构的研究进展

随着材料性能的不断提升,近年来纳米陷光结构在钙钛矿电池中的应用受到越来越多的关注.纳米陷光结构的引入可以改变光子在电池中的传输路径以及被电池吸收的光子能量.将纳米陷光结构用于钙钛矿电池中的不同界面可以不同程度地增加电池对光的吸收,最终提升电池效率.如何有效地应用陷光结构是进一步提升钙钛矿电池转换效率的关键问题之一.本文从阐述具有不同纳米陷光结构的钙钛矿电池性能出发,对不同结构进行了对比与总结,并分析了其中的优势与劣势.     

Effectiveness of full spectrum light soaking on solar cell degradation analysis

This study examined the effect of UV-spectrum light soaking on solar cell degradation tests. An indoor light soaking test was evaluated over three different spectral ranges: “UV only”, “UV blocked” and “Full spectrum”. a-Si:H and poly-crystalline silicon solar cell technologies were studied by light soaking tests with the same optical filter configurations.The I–V measurement results demonstrated that “UV only” irradiated solar cells exhibited the smallest output power degradation, which was only half of a percent variation compared with the full spectrum light soaking case. Using a filter that excluded the effect of the UV spectral range on light soaking, the “UV blocked” case also exhibited a significant output power degradation of the solar cells. A comparative analysis of the solar cell response, based on the I–V characteristics and the diode ideality factor under these different light soaking spectra, demonstrated the importance of the full spectrum light soaking test in the evaluation of the long-term performance of solar cells.     

Modeling and simulation of experimentally fabricated QDSSC using ZnS as light absorbing and blocking layer

Abstract—Two main factors which limit the power conversion efficiency of solar cells are light absorption and recombination processes. In photovoltaic (PV) devices, low energy photons cannot be absorbed and excite electrons from valance band to conduction band, hence do not contribute to the current. On the other hand, high energy photons cannot be efficiently used due to a poor match to the energy gap. Existence of charge recombination in PV devices causes the low conversion performance, which is indicated by the low open-circuit voltage (V _OC ). Using a blocking layer in system could effectively reduce the recombination of charge carriers. In this study, we simulated a solar cell with ITO/ZnO/P3HT&PCBM/Ag structure. To prevent the charge recombination, a ZnS QD layer was used which acts as a light absorbing and a recombination blocking layer in the ITO/ZnO film/ZnS QD/P3HT&PCBM/Ag structure. The simulated J–V characteristics of solar cells showed a close match with the experimental results. Simulate data showed an increase of conversion efficiency in ZnS QDSSC from 1.71 to 3.10%, which is relatively 81.28% increase.     

Analysis of sunlight loss for femtosecond laser microstructed silicon and its solar cell efficiency

Black silicon, which is obtained by irradiating the surface of a Si wafer with femtosecond laser pulses in the presence of a sulfur-bearing gas, holds great promise in the preparation of high-performance intermediate band silicon solar cells. Using a three-level model, the enhanced usefulness of sunlight of the microstructured silicon was firstly analyzed. A detailed study on the relationship between the light loss, the ionization energy of doped impurities in silicon and the impurity band width were given. Then the effect of the position of intermediate band within the forbidden gap of silicon on the theoretical conversion efficiency for the corresponding solar cell is discussed using the Detailed Balance Theory. Finally problems need to be resolved in making intermediate band solar cells based on femtosecond laser microstructured silicon are pointed out with great emphasis.     

Buffer-less Cu(In,Ga)Se2 solar cells by band offset control using novel transparent electrode

Cu(In,Ga)Se₂ (CIGS) solar cells without buffer layers have been demonstrated. Currently, CdS, Zn(O,S,OH), ZnS, or InS buffer layers are used in high efficiency CIGS solar cells to suppress interface recombination. One of the important parameters to reduce the recombination is the conduction band offset (CBO) between the buffer and CIGS layers. In this study, we have proposed the use of a novel transparent conductive oxide (TCO) which can control the CBO to reduce interface recombination and eliminate the buffer layers. The device simulation was used to verify the effect of CBO control theoretically. Then, the novel TCO material of ZnO_1?xS_x:Al prepared by co-sputtering of ZnO:Al₂O₃ and ZnS targets was fabricated to verify the CBO effect experimentally. The efficiency of a CIGS solar cell with a ZnO:Al/CIGS/Mo/soda-lime glass structure, i.e. buffer-less structure using a conventional TCO, was significantly low because of severe shunting. In contrast, the use of ZnO_1-xS_x:Al instead of ZnO:Al increased the shunt resistance of the CIGS solar cell, resulting in higher open-circuit voltage and efficiency. The result is the first proof of the concept of the buffer-less CIGS solar cells.     

Electrical and optical properties of nanowires based solar cell with radial p-n junction

In our studies the absorption, transmittance and reflectance spectra for periodic nanostructures with different parameters were calculated by the FDTD (Finite-Difference Time-Domain) method. It is shown that the proportion of reflected light in periodic structures is smaller than in case of thin films. The experimental results showed the light reflectance in the spectral range of 400–900 nm lower than 1% and it was significantly lower in comparison with surface texturing by pyramids or porous silicon.Silicon nanowires on p-type Si substrate were formed by the Metal-Assisted Chemical Etching method (MacEtch). At solar cells with radial p-n junction formation the thermal diffusion of phosphorus has been used at 790 °C. Such low temperature ensures the formation of an ultra-shallow p-n junction. Investigation of the photoelectrical properties of solar cells was carried out under light illumination with an intensity of 100 mW/cm². The obtained parameters of NWs' solar cell were I_sc = 22 mA/cm², U_oc = 0.62 V, FF = 0.51 for an overall efficiency η = 7%. The relatively low efficiency of obtained SiNWs solar cells is attributed to the excessive surface recombination at high surface areas of SiNWs and high series resistance.     

A first-principles study of the electronic structure of the sulvanite compounds

We have investigated by means of first-principles total energy calculations the electronic structure of the sulvanite compounds: Cu₃VS₄, Cu₃NbS₄ and Cu₃TaS₄; the later is a possible candidate as a p-type transparent conductor with potential applications in solar cells and electrochromic devices. The calculated electronic structure shows that these compounds are indirect band gap semiconductors, with the valence band maximum located at the R-point and the conduction band minimum located at the X-point. The character of the valence band maximum is dominated by Cu d-states and the character of the conduction band minimum is due to the d-states of the group five elements. From the calculated charge density and electron localisation function we can conclude that the sulvanite compounds are polar covalent semiconductors.