Class Of Solar Cells Research Articles

Abnormal Dynamic Reverse Bias Behavior and Variable Reverse Breakdown Voltage of ETL‐free Perovskite Solar Cells

Perovskite solar cells (PSCs) have shown an impressive power conversion efficiency of 26.1%, while their upcoming commercialization urgently needs to solve the stability problem. Among numerous stability issues of PSCs, little attention is paid to reverse bias stability. When some cells of the module are shaded by irresistible factors, this will cause the current of the illuminated part to flow through the shaded cells as a reverse current and force them to be under reverse bias. Herein, the breakdown mechanism dominated by different reverse bias regions of a prototype electron transport layer free PSCs is distinguished. And, it is confirmed that PSCs present a thought‐provoking dynamic reverse bias (DRB) behavior and variable reverse breakdown voltage (VRB), which is essentially distinct from classic solar cells. Specifically, VRB is significantly affected by voltage scan rate, range and direction, and illumination. The underlying mechanism is explained by drift‐diffusion modeling taking into account the electric field generated by directional ion migration. The latter can hinder the movement of charge carriers and cause the observed variable VRB and DRB behavior. Predictably, the understanding of the dynamic process is crucial to establish a standard VRB measurement procedure and further promote the commercialization of PSCs.

Sodium Fluoride Doping Approach to CdTe Solar Cells

Sodium is a common impurity in CdTe solar cells, yet there are relatively few reports investigating its effect on complete device structures. There is the potential for uncontrolled sodium incorporation, either from impurities in the CdTe material itself or contaminants introduced during device processing, which can affect the optoelectronic properties of CdTe. Therefore, it is important to consider the impact of sodium incorporation on device performance. In this work, we show that the deposition of a thin layer of NaF at the back surface of CdS/CdTe devices prior to metallization is an effective strategy to form a highly doped back surface and improve contact quality. High temperature (∼300 °C) annealing is required to effectively incorporate sodium throughout the device and improve the bulk doping density; however, this also leads to sodium accumulation in the CdS layer and the formation of a TeO2 layer at the back surface. We also find evidence of out-diffusion of sodium from commonly used TEC glass substrates at typical CdTe processing temperatures, despite the presence of an alkali diffusion barrier layer. Understanding this prevalent sodium diffusion in this class of solar cells is vital for further improvement of CdTe structures.

Dielectric Junction: Electrostatic Design for Charge Carrier Collection in Solar Cells

Conventional solar cells typically use doping of the involved semiconducting layers and work function differences between highly conductive contacts for the electrostatic design and the charge selectivity of the junction. In some halide perovskite solar cells, however, substantial variations in the permittivity of different organic and inorganic semiconducting layers strongly affect the electrostatic potential and thereby indirectly also the carrier concentrations, recombination rates, and eventually efficiencies of the device. Here, numerical simulations are used to study the implications of electrostatics on device performance for classical p−n junctions and p−i−n junctions, and for device geometries as observed in perovskite photovoltaics, where high‐permittivity absorber layers are surrounded by low‐permittivity and often also low‐conductivity charge transport layers. The key principle of device design in materials with sufficiently high mobilities that are still dominated by defect‐assisted recombination is the minimization of volume with similar densities of electrons and holes. In classical solar cells this is achieved by doping. For perovskites, the concept of a dielectric junction is proposed by the selection of charge transport layers with adapted permittivity if doping is not sufficient.

Doping effect of chalcogens on electronic and optical properties of perovskite LiNbO3 compound: Ab initio calculations

In this study, the effects of Sulfur (S), Selenium (Se), and Tellurium (Te) on the electronic and optical properties of LiNbO 3 were studied by using density functional theory (DFT) within Wien2k code based on the generalized gradient approximation (GGA-PBE). Analyses of the studied components revealed that the incorporation of chalcogens in LiNbO 3 effectively reduces the electronic band-gap and that varying the amount and the type of dopant can control the level of band-gap reduction. The band-gap is equal to 2.312 eV, 1.996 eV, and 0.924 eV for 11.11% S, Se, and Te doped LiNbO 3, respectively. For the pure LiNbO 3 , the band-gap is 3.544 eV. Moreover, the absorption is improved in the visible light (380–790 nm) and exceeds 10 5 cm −1 for Te doped-LiNbO 3 . The dielectric constant at zero frequency (ε 1 (0)) is equal to 5.254 for LiNbO 3 and 8.531 for Te doped-LiNbO 3 : 11.11%. Optical conductivity and reflectivity are predicted and the results showed that increasing chalcogens concentration considerably improves the electrical conductivity. Comparisons between the three types of doping were also performed and the results indicated that Te would be the best substitute for oxygen in LiNbO 3; hence ensuring a promising and environmentally friendly new class of solar cells.

Advanced Materials for Photovoltaic Energy Harvesting

Design of novel materials is the key to ground breaking advancements in energy conversion. Solar radiation is a clean energy source with low environment impact but is still a difficult technology to be implemented on a large scale because of being an expensive technology. If global demands are to be met, new classes of solar cells with increased efficiency, reduced cost and new form factors must be developed. A lot of research is ongoing to find efficient materials which can supplement or supersede the existing silicon technology. In this review a general introduction covers the current scenario of energy demands of the world and where we stand in the search for alternative energy resources. A brief look into the working of photovoltaic systems and the conditions required to fabricate an ideal solar cell follows. Some of the advanced systems incorporated in solar cells over the past 20 years.

A Bayesian approach to luminescent down-conversion.

Photon conversion embodies a range of promising possibilities in pushing the theoretical Shockley-Queisser efficiency model of classical solar cells. Luminescent down-conversion, despite its potential, is held back in practical applications due to the difficulty of proper characterization in no small part because of concurrent luminescent downshifting events. Recent advances have demonstrated the opportunity provided by photon correlation measurement for down-conversion characterization. In this methodological work, we present a general method based on Bayesian probabilities for deriving auto-correlation functions analytically. This method is then applied to the five down-conversion mechanisms reported in the literature and successfully tested against numerical simulations. We show that the zero delay auto-correlation function can be the most direct way to demonstrate down-conversion and assess its efficiency. Our analysis offers additional useful tools for the design of characterization experiments and emphasizes some universal behavior valid for all reported conversion mechanisms.

The structural effects on performance of a lateral AlGaAs/GaAs quantum well solar cell

This paper introduces a novel lateral quantum well solar cell, and investigates the effects of structural parameters of these nanostructures on the device’s performance. For modeling the device, first, the absorption coefficients and the reflectance parameters of the device at different regions were calculated. Those parameters were then used to find the system’s optical generation rate. Finally, while considering all the radiative and non-radiative recombinations, the continuity and drift-diffusion equations were solved to find the dark- and photo-currents. The results indicated that applying quantum wells to the traditional classical solar cells could noticeably increase the system’s efficiency. Additionally, it was found that efficiency was heavily dependent on the values of different geometrical parameters, including the active layer’s thickness and the width of the wells and barriers. Moreover, it was shown that modifying some structural parameters such as the barrier mole fraction could noticeably influence the solar cell’s characteristics. Therefore, to obtain good efficiency it is necessary to optimize these parameters.

Effect of Plasmonic Nanoparticles on the Electric Field Strength to Improve Performance of Single Crystalline Solar Cell

The effect of metal nanoparticles (MNPs) on the electric field strength and distribution for improvement solar cell performance is investigated and simulated. By manipulating the properties of nanoparticles, distribution of the electric field was altered. In this paper, classical solar cell (p-n junction) and improved structure (add an extra layer of SiO2 and gold nanoparticles on the top of p-n junction) is simulated. Different sizes of NPs, thickness of SiO2 sublayer, and spacing distance between NPs is done to improving the electric field and showing plamonic effect. Gold NPs deposition on single crystalline silicon solar cell is modelled by COMSOL 5.2 2D, Electromagnetic wave propagation in the frequency domain with periodic boundary conditions. The best wavelength found in our work is 550 nm. The electric field enhances when the size of NPs increases but it must be limited. When gold NPs are deposited on the SiO2 sublayer, the plasmonic effect appears due to decreasing the refractive index. Moreover, separation distance between NPs affect the electric field enhancement by manipulating the number of NPs, the distance decreases and the plasmonic interaction appears.

Charge Transport between Coaxial Polymer Nanorods and Grafted All-Inorganic Perovskite Nanocrystals for Hybrid Organic Solar Cells with Enhanced Photoconversion Efficiency

The versatile optoelectronic properties of perovskite nanocrystals (NCs) have provided a strong surge for their utilization in different classes of solar cells, with organic photovoltaic systems being no exception. In an unprecedented approach, a hybrid solar cell with CsPbBr1.5I1.5 NCs strategically grafted on poly(3-hexylthiophene-2,5-diyl) (P3HT) nanorods (NRs) is shown to have a photoconversion efficiency of 9.72 ± 0.4%, with only 1.5 wt % NCs. The improvement is twice more than the P3HT:PCBM reference devices (4.09 ± 0.2%). The choice of NC composition is validated by density functional theory calculations, which show decent charge carrier mobility in CsPbBr1.5I1.5, besides having better stability than CsPbI3, making CsPbBr1.5I1.5 NCs a suitable contender for hybrid device architecture. A trivial blending of the NCs in the P3HT:PCBM matrix results in their nonuniform distribution, escalating charge carrier trapping, albeit maintaining a device efficiency of 8.07 ± 0.3% with 1 wt % NCs. Uniform NC grafting is propitious over inhomogeneous blending because CsPbBr1.5I1.5 NCs not only act as additional light harvesters, but their chemical grafting onto the P3HT NRs improves the charge transport by creating better charge percolation pathways. The higher crystallinity of the P3HT NRs than P3HT also helps in reducing the trap states.

Photonic effect of a central ultrathin metal film on the performance of series and parallel homo-tandem solar cells

We compare the performances of single cells, parallel and series homo-tandem solar cells by focusing on the effect of a central ultra thin metal film acting as an interconnecting layer in the series case or as an electrode in the parallel case. Cells with this metal film are found to outperform classic solar cells thanks to better interference management. Moreover, we find that photonic optimization from an absorption point of view can be accompanied by a reduction of the total amount of active material. We show that the best types of cell strongly depends on the maximum allowed active material thickness to ensure good carrier collection. We also compare ITO and a recently devised ITO-free alternative, the Two-Resonance Tapping Cavity, as transparent electrode and we show how this choice influences photonic optimization. We perform our analysis under the assumption of AM1.5 spectral illumination for a wide choice of realistic materials: PTB7-th:PC71BM, P3HT:PC61BM and DBP:C70, as well as a theoretical material with a Shockley-Queiser type of spectral absorption plus an Urbach tail. With this idealized spectral response, one can capture all the fundamental features and draw general conclusions about optimization of homo-tandem cells.

Ti3C2Tx (MXene)‐Silicon Heterojunction for Efficient Photovoltaic Cells

AbstractA novel type of solar cell has been developed based on charge separation at the heterojunction formed by a transparent conducting MXene electrode and an n‐type silicon (n‐Si) wafer. A thin layer of the native silicon dioxide plays an important role in suppressing the recombination of charge carriers. A two‐step chemical treatment can increase the device efficiency by about 40%. Promisingly, an average power conversion efficiency of over 10% under simulated full sunlight is achieved for this novel class of solar cell with the application of an antireflection layer. The efficiencies of these novel solar cells based on a MXene‐Si heterojunction achieved in this work point to great promise in emerging photovoltaic technology. In addition to their high efficiency, the excellent reproducibility of such devices establishes a solid base for possible future commercialization.

Manufacturing of All Inkjet-Printed Organic Photovoltaic Cell Arrays and Evaluating their Suitability for Flexible Electronics.

The generation of electrical energy depending on renewable sources is rapidly growing and gaining serious attention due to its green sustainability. With fewer adverse impacts on the environment, the sun is considered as a nearly infinite source of renewable energy in the production of electrical energy using photovoltaic devices. On the other end, organic photovoltaic (OPV) is the class of solar cells that offers several advantages such as mechanical flexibility, solution processability, environmental friendliness, and being lightweight. In this research, we demonstrate the manufacturing route for printed OPV device arrays based on conventional architecture and using inkjet printing technology over an industrial platform. Inkjet technology is presently considered to be one of the most matured digital manufacturing technologies because it offers inherent additive nature and last stage customization flexibility (if the main goal is to obtain custom design devices). In this research paper, commercially available electronically functional inks were carefully selected and then implemented to show the importance of compatibility between OPV material stacks and the device architecture. One of the main outcomes of this work is that the manufacturing of the OPV devices was accomplished using inkjet technology in massive numbers ranging up to 1500 containing different device sizes, all of which were deposited on a flexible polymeric film and under normal atmospheric conditions. In this investigation, it was found that with a set of correct functional materials and architecture, a manufacturing yield of more than 85% could be accomplished, which would reflect high manufacturing repeatability, deposition accuracy, and processability of the inkjet technology.

Fabrication and Characterization of Organic Photovoltaic Cell using Keithley 2400 SMU for efficient solar cell

An organic solar cell device or organic photovoltaic cell (OPV) is a class of solar cell that uses conductive organic polymers or small organic molecules for light absorption and charge transport. In this study, we fabricate and characterize an organic photovoltaic cell device and estimated important parameters of the device such as Open Circuit Voltage Voc of 0.28V, Short-Circuit Current Isc of 4.0 × 10-5 A, Maximum Power Pmax of 2.4 × 10-6 W, Fill Factor of 0.214 and the energy conversion efficiency of η=0.00239% were tested using Keithley 2400,source meter under A.M 1.5 (1000/m2) illumination from a Newport Class A solar simulator. Also the I-V characteristics for OPV were drawn.

Purple power leaves the window open

Solar Cells Certain tunable coatings can render windows “smart” by modulating the amount of heat and light passing through them, depending on the desired temperature indoors. Powering these windows with photovoltaics seems sensible, but it is inefficient for the power source to absorb the same light that the coating is meant to regulate. Davy et al. resolve this conundrum by preparing a class of solar cells that absorb at the boundary between violet and ultraviolet. Composed from hexabenzocoronene organic semiconductors, these cells interfaced effectively with electrochromic window coatings on square-centimeter scales, leaving the rest of the optical and near-infrared regime open for modulation. Nat. Energy 2 , 17104 (2017).

Design and characterization of hydrogel-based microfluidic devices with biomimetic solute transport networks.

Hydrogel could serve as a matrix material of new classes of solar cells and photoreactors with embedded microfluidic networks. These devices mimic the structure and function of plant leaves, which are a natural soft matter based microfluidic system. These unusual microfluidic-hydrogel devices with fluid-penetrable medium operate on the basis of convective-diffusive mechanism, where the liquid is transported between the non-connected channels via molecular permeation through the hydrogel. We define three key designs of such hydrogel devices, having linear, T-shaped, and branched channels and report results of numerical simulation of the process of their infusion with solute carried by the incoming fluid. The computational procedure takes into account both pressure-driven convection and concentration gradient-driven diffusion in the permeable gel matrix. We define the criteria for evaluation of the fluid infusion rate, uniformity, solute loss by outflow and overall performance. The T-shaped channel network was identified as the most efficient one and was improved further by investigating the effect of the channel-end secondary branches. Our parallel experimental data on the pattern of solute infusions are in excellent agreement with the simulation. These network designs can be applied to a broad range of novel microfluidic materials and soft matter devices with distributed microchannel networks.

Dye-sensitized solar cell for a solar concentrator system

The performances of a photovoltaic system based on dye-sensitized solar cells associated with a solar concentrator are investigated. An extensive indoor characterization is performed using both different wavelength bandwidths and concentration ratio. Starting from the acquired data, the system coupled with a solar tracking is also tested in outdoor condition. The obtained results show that it is possible to use this class of solar cells in solar concentrator systems, leading to a new class of devices with a high efficiency and a low cost.

ペロブスカイト太陽電池へのITO透明電極スパッタリング直接堆積の影響

Thin film solar cells using perovskite materials are very intensively studied since the perovskite materials such as CH3NH3PbI3 crystal have been found to show sensitizing effects on a TiO2 electron transport layer. This class of solar cell has made tremendous progress during the last few years, leading to a recently certified record power conversion efficiency (PCE) of 21.02%. In the perovskite /crystalline-Si (c-Si) tandem solar cell, furthermore, the theoretical value of PCE is expected as large as 35 %. Toward this application, the perovskite solar cell must be highly transparent at near-infrared wavelengths so that sufficient light is transmitted to the narrow-bandgap bottom cell. In this study, we fabricated the organic-lead halide perovskite solar cells comprising a transparent sputtered indium tin oxide (ITO) top electrode. We observed the PCE of 1.5% in transparent perovskite solar cells with a thin molybdenum oxide buffer layer and ITO electrode. Moreover, we obtained the PCE of 2% even in solar cells with ITO electrode sputtered directly on the organic charge transport layer. The photovoltaic property could be confirmed under the light irradiation from the ITO top electrode side.

A Physics-Based Analytical Model for Perovskite Solar Cells

Perovskites are promising next-generation absorber materials for low-cost and high-efficiency solar cells. Although perovskite cells are configured similar to the classical solar cells, their operation is unique and requires development of a new physical model for characterization, optimization of the cells, and prediction of the panel performance. In this paper, we develop such a physics-based analytical model to describe the operation of different types of perovskite solar cells, explicitly accounting for nonuniform generation, carrier selective transport layers, and voltage-dependent carrier collection. The model would allow experimentalists to characterize key parameters of existing cells, understand performance bottlenecks, and predict performance of perovskite-based solar panel - the obvious next step to the evolution of perovskite solar cell technology.

Effect of the Vertical Transportation Component of the TCO Layer on the Electrical Properties of Silicon Heterojunction Solar Cells

Silicon heterojunction (SHJ) solar cells that consist of thin amorphous silicon layers and crystalline silicon substrate are known as the high-efficiency class of solar cells. To collect the charge carriers, transparent conductive oxide (TCO) layers are inserted in which the charge carriers are being either vertically or both laterally and vertically transported. In this study, we have investigated the effect of the vertical transportation component of aluminum-doped zinc oxide (AZO) layers on the electrical properties of the fabricated SHJ solar cells and its contribution to the total series resistance of the obtained devices. In order to separate the vertical from the lateral transportation, we have employed an AZO/Ag/AZO multilayer structure, which only allows the vertical transportation of the charge carriers within the AZO layers. Our results show that with increase in O2 flow, the reduction rate of the FF is about three times higher when both lateral and vertical conductions take place, compared with when only vertical conduction occurs. Moreover in the latter case, a reduction of ~ 6% in the FF value per unit increase of vertical resistivity is obtained. Finally, we validate our procedure by comparing the obtained experimental results with the theoretically modeled values. The validation delivered a good agreement.

Photovoltaic efficiency limits and material disorder

Solar cells based on crystalline semiconductors such as Si and GaAs provide nowadays the highest performance, but photovoltaic (PV) cells based on less pure materials, such as poly- or nano-crystalline or amorphous inorganic or organic materials, or a combination of these, should relax production requirements and lower the cost towards reliable, sustainable and economic electrical power from sunlight. So as to be able to compare the operation of different classes of solar cells we first summarize general photovoltaic principles and then consider implications of using less than ideal materials. In general, lower material purity means more disorder, which introduces a broad distribution of energy states of the electronic carriers that affects all the aspects of PV performance, from light absorption to the generation of voltage and current. Specifically, disorder penalizes energy output by enhanced recombination, with respect to the radiative limit, and also imposes a lowering of quasi-Fermi levels into the gap, which decreases their separation, i.e., reduces the photovoltage. In solar cells based on organic absorbers, such as dye-sensitized or bulk heterojunction solar cells, vibronic effects cause relaxation of carriers in the absorber, which implies an energy price in terms of obtainable output.