Graphene Solar Cells Research Articles

Development of directly grown‐graphene–silicon Schottky barrier solar cell using co‐doping technique

Low-cost, highly efficient, and low-power devices are essential for energy harvesting applications. Despite numerous studies having been conducted on transferable graphene solar cells, large-area growth and long-term stability continue to remain elusive, which limits the practicability of graphene-based photovoltaic devices. Plasma-enhanced chemical vapor deposition is a promising, efficient, and facile method for synthesizing graphene over a large area without the use of a metal catalyst, but defects formed during graphene growth adversely affect the power conversion efficiency (PCE) of graphene/Si solar cells in which the graphene is used. In this work, we successfully employed acid-based graphene-Si macromolecular photovoltaic devices chemically doped with polymeric perfluorinated sulfonic acid (PFSA) macromolecules and nitric acid (HNO3). We achieved an improved PCE of about 9.27% with PFSA doping compared with the value (7.64%) without PFSA doping, and it increased substantially to 10.44% after co-doping with HNO3. PFSA macromolecular doping also led to a substantial increase in the carrier concentration, which helped to reduce the sheet resistance of graphene and improved the work function of the device. In particular, the synergistic effect of co-doping with HNO3 helped to improve the number of active sites and charge separation. Along with the increase in carrier concentration, doping with PFSA reduced the number of defects, resulting in the graphene having a smooth and uniform surface, which effectively increased the open-circuit voltage (Voc) from 0.500 to 0.521 V. We surmise that nonvolatile PFSA macromolecular and volatile HNO3 co-doping has high potential for use in the fabrication of low-cost directly grown-graphene-based photovoltaic devices. Highlights Plasma-enhanced chemical vapor deposition technique used for the direct growth of graphene without metal catalyst. Naturally grown oxide thickness optimized. Nonvolatile macromolecular dopant per-fluorinated polymeric sulfonic acid (PFSA) and volatile nitric acid (HNO3) were used for direct growth graphene doping. The power conversion efficiency of ~9.27% with PFSA doping from 7.64%; further, its substantial increase up to 10.44% after co-doping with HNO3 were achieved with long-term stability.

The role of oxygen defects engineering via passivation of the Al2O3 interfacial layer for the direct growth of a graphene-silicon Schottky junction solar cell

Over the past decade, graphene-based solar cells have received increasing exploration. In particular, the metal–insulator–semiconductor (MIS)-type solar cells have an inherent cost advantage compared to the p-n junction solar cells. However, the technological progress in graphene solar cells based on the MIS junction is currently facing a number of serious challenges, including long-term stability, surface recombination at the interface level, and surface defects. To overcome these barriers, a simple, cost-effective method is developed herein for the interfacial single-component passivation of Al2O3 with NH3 or H2O2, and co-passivation with NH3 and H2O2 together. The interfacial layer between the silicon and the directly-grown graphene operates as an effective electron blocking layer, thus leading to the minimization of surface recombination. Further, the NH3-H2O2 co-passivated Al2O3 performs the dual role of providing a good platform for the growth of graphene and enhancing the performance of the fabricated solar cell. Moreover, in a proof of concept demonstration, the fabricated graphene-silicon (Gr/Si) Schottky junction with an NH3-H2O2 co-passivated Al2O3 interfacial layer exhibits an efficiency of 9.49%, which is a major enhancement over that of the Gr/Si solar cell without an interfacial layer (i.e., 3.19%). These results demonstrate that the control of oxygen-related defects containing non-lattice oxygen in the Al2O3 interfacial layer remarkably impacts the charge transfer resistance and electron recombination processes. This work can be viewed as an elegant interface engineering approach to the co-passivation of Al2O3 for optoelectronic applications.

Design of high performance and low resistive loss graphene solar cells

Despite metallic plasmonic excitations can enhance the performance of ultra-thin solar cells however these so-called plasmonic solar cells suffer from a large resistive (Ohmic) loss caused by metallic elements. In this work, we report on a new design that uses graphene nanoribbons (GNRs) in a two-dimensional (2D) grating form at the top of the semiconductor-on-insulator (SOI) solar cells aimed to reduce the resistive loss. The results showed that GNRs can remarkably reduce the resistive loss compared to the SOI cell with Ag nanograting, while keeping all other cell’s parameters, comparable with those of Ag SOI cell. Optical absorption and short-circuit current density of the graphene cells showed, respectively, enhancements of 18 and 1.7 times when optimizations were done with respect to width and the grating period. Our calculations showed that the graphene solar cells dissipate at most 5% of incident sunlight power as narrow and tiny peaks around 508 nm, which is noticeably lower than those of Ag solar cells with high and broad band peaks with the maximum values of 29% at 480 nm and 24% at 637 nm.

Tuneable efficiency of direct growth graphene solar cells

Tuneable efficiency of direct growth graphene solar cells

SCAPS Simulation on P3HT:Graphene Nanocomposites Based Bulk-Heterojunction Organic Solar Cells

There has been an increasing interest towards organic solar cells after the discovery of conjugated polymer and bulk-heterojunction concept. Eventhough organic solar cells are less expensive than inorganic solar cells but the power conversion energy is still considered low. The main objective of this research is to investigate the effect of the P3HT’s thickness and concentration towards the efficiency of the P3HT:Graphene solar cells. A simulation software that is specialize for photovoltaic called SCAPS is used in this research to simulate the effect on the solar cells. The solar cell’s structure will be drawn inside the simulation and the parameters for each layers is inserted. The result such as the open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF), efficiency (η), capacitance-voltage (C-V) and capacitance-frequency (C-f) characteristic will be calculated by the software and all the results will be put into one graph.

Advanced interface modelling of n-Si/HNO3 doped graphene solar cells to identify pathways to high efficiency

In graphene/silicon solar cells, it is crucial to understand the transport mechanism of the graphene/silicon interface to further improve power conversion efficiency. Until now, the transport mechanism has been predominantly simplified as an ideal Schottky junction. However, such an ideal Schottky contact is never realised experimentally. According to literature, doped graphene shows the properties of a semiconductor, therefore, it is physically more accurate to model graphene/silicon junction as a Heterojunction. In this work, HNO3-doped graphene/silicon solar cells were fabricated with the power conversion efficiency of 9.45%. Extensive characterization and first-principles calculations were carried out to establish an advanced technology computer-aided design (TCAD) model, where p-doped graphene forms a straddling heterojunction with the n-type silicon. In comparison with the simple Schottky junction models, our TCAD model paves the way for thorough investigation on the sensitivity of solar cell performance to graphene properties like electron affinity. According to the TCAD heterojunction model, the cell performance can be improved up to 22.5% after optimizations of the antireflection coatings and the rear structure, highlighting the great potentials for fabricating high efficiency graphene/silicon solar cells and other optoelectronic devices.

Prospects of Graphene as a Potential Carrier-Transport Material in Third-Generation Solar Cells.

Third-generation solar cells are understood to be the pathway to overcoming the issues and drawbacks of the existing solar cell technologies. Since the introduction of graphene in solar cells, it has been providing attractive properties for the next generation of solar cells. Currently, there are more theoretical predictions rather than practical recognitions in third-generation solar cells. Some of the potential of graphene has been explored in organic photovoltaics (OPVs) and dye-sensitized solar cells (DSSCs), but it has yet to be fully comprehended in the recent third-generation inorganic-organic hybrid perovskite solar cells. In this review, the diverse role of graphene in third-generation OPVs and DSSCs will be deliberated to provide an insight on the prospects and challenges of graphene in inorganic-organic hybrid perovskite solar cells.

Energy-level alignment and open-circuit voltage at graphene/polymer interfaces: theory and experiment

Functionalized graphene promises to become a key component of novel solar cell architectures, owing to its versatile ability to act either as transparent conductor, electron acceptor, or buffer layer. In spite of this promise, the solar energy conversion efficiency of graphene-based devices falls short of the performance of competing solution-processable photovoltaic technologies. Here we address the question of the maximum achievable open-circuit voltage of all-organic graphene: polymer solar cells using a combined theoretical/experimental approach, going from the atomic scale level to the device level. Our calculations on very large atomistic models of the graphene/polymer interface indicate that the ideal open-circuit voltage approaches one volt, and that epoxide functional groups can have a dramatic effect on the photovoltage. Our predictions are confirmed by direct measurements on complete devices where we control the concentration of functional groups via chemical reduction. Our findings indicate that the selective removal of epoxide groups and the use of ultradisperse polymers are key to achieving graphene solar cells with improved energy conversion efficiency.

Enhanced Power Conversion Efficiency of Graphene/Silicon Heterojunction Solar Cells Through NiO Induced Doping.

We report a doping strategy, where nickel oxide (NiO) nanoparticle film coating is employed for graphene/Si heterojunction solar cells to improve the power conversion efficiency (PCE). NiO doping has been shown to improve the short circuit current (J(SC)) by 12%, open circuit voltage (V(OC)) by 25% and fill factor (FF) by 145% of the cells, in turn increasing the PCE from 1.37% to 4.91%. Furthermore, NiO doped graphene/Si solar cells don't show any significant performance degradation over 10 days revealing that NiO doping can be a promising approach for practical applications of graphene in solar cells.

Capacitance Voltage of P3HT:Graphene Nanocomposites Based Bulk-Heterojunction Organic Solar Cells

After the discovery of conjugated polymer and bulk-heterojunction concept, organic solar cell has gain many interest in the photovoltaic world. The main problem for organic solar cells is that the power conversion efficiency (PCE) is still considered low even though it is much more low cost compared to inorganic solar cell such as Silicon (Si). Therefore, the objective of this research is to investigate the effect of Poly(3-hexylthiophene) (P3HT) thickness and concentration towards the capacitance voltage of the P3HT:Graphene solar cells. A simulation software called SCAPS is used in this research to simulate the effect on the solar cells. SCAPS is specialized for photovoltaic simulation studies. The solar cell's structure will be drawn inside the simulation and the parameters for each layers is inserted. The voltage range will be fixed and the capacitance voltage will be calculated by the software and all the results will be put into one graph. For thickness results, P3HT's layer at a thickness of 100nm has the lowest value of capacitance and clearly shows a peak at 0.86V. Where for the concentration, 1×1016 cm-3 is the only value that clearly shows there is the built-in voltage (Vbi) in the solar cells. Therefore, P3HT's thickness of 100 nm and concentration of 1×1016 cm−3 has the best overall results.

Structured Single-Walled Carbon Nanotubes and Graphene for Solar Cells.

We propose the concept of structured single-walled carbon nanotubes (SWNTs) for the applications of heterojunction solar cells and dye-sensitized solar cells (DSSCs). The structure of SWNTs was controlled and modified by a simple water vapor treatment, which was originally developed by our group. Compared with the graphene-Si solar cell and the SWNT-Si solar cell using the random-oriented SWNT film, the pristine micro-honeycomb structured SWNT-Si solar cell shows a significant improvement in terms of fill factor and the greater potential to obtain high power conversion efficiency (PCE). Moreover, the performance of the pristine micro-honeycomb structured SWNT-Si solar cells is stable in ambient condition. In addition, the PCE and fill factor of the DSSC with the micro-honeycomb structured SWNT counter electrode are 3.90% and 0.61, respectively, which are comparable to those of the DSSC with Pt as the counter electrode. This result shows that the micro-honeycomb networked SWNTs provide a low-cost alternative to replace Pt in DSSCs.

Graphene in Solar Cells

Graphene in Solar Cells

Solar Cell Made Using Graphene

The principal objective of this paper is to demonstrate the capability of graphene in making energy efficient solar panels inexpensively. Comparing to silicon solar cells , graphene solar cells are more efficient and provides double the power output in less time. Checking out the difference for the selection of elements between silicon and graphene, graphene leads with respect to properties like electrical conductivity, thermal conductivity, material strength and flexibility. The main difference is its inexpensiveness. Where there is increase in population and insufficient power production in villages ,small scale industries ,graphene solar panels will be installed to gain additional power without any problem .Researchers and industrialists quote graphene as the nearby future for power supply.

Energy Focus: Chemical doping helps break efficiency record for graphene solar cells

Energy Focus: Chemical doping helps break efficiency record for graphene solar cells

High Efficiency Graphene Solar Cells by Chemical Doping

We demonstrate single layer graphene/n-Si Schottky junction solar cells that under AM1.5 illumination exhibit a power conversion efficiency (PCE) of 8.6%. This performance, achieved by doping the graphene with bis(trifluoromethanesulfonyl)amide, exceeds the native (undoped) device performance by a factor of 4.5 and is the highest PCE reported for graphene-based solar cells to date. Current-voltage, capacitance-voltage, and external quantum efficiency measurements show the enhancement to be due to the doping-induced shift in the graphene chemical potential that increases the graphene carrier density (decreasing the cell series resistance) and increases the cell's built-in potential (increasing the open circuit voltage) both of which improve the solar cell fill factor.

新一代太阳电池的设计思想及研究进展 Design Concepts and Research Progress of New Generation Solar Cells

本文综述了太阳电池的发展趋势、研究热点及存在问题。在此基础上，从太阳光谱充分利用和材料设计角度，讨论了聚光型电池、多结叠层电池、中间带电池、上下转换器电池、纳米线(柱)阵列电池、量子点多激发电池、热载流子电池、热光伏电池、纳米天线电池、石墨烯电池等新一代太阳电池的设计思想及研究现状。 This paper briefly reviews the prospects, research focus, and problems of solar cells. Based on it, the primary design concepts and research progress of new generation solar cells including sunlight-concentrated, multi-junction, intermediate band, up conversion and down conversion, nanowire or nanopillar array, multi-exciton generation, hot carrier, thermophotovoltaic (TPV), nanoscale antenna, and graphene solar cells, etc., are discussed from the viewpoint of the full utilization of sunlight energy and material design.

Continuous, Highly Flexible, and Transparent Graphene Films by Chemical Vapor Deposition for Organic Photovoltaics

We report the implementation of continuous, highly flexible, and transparent graphene films obtained by chemical vapor deposition (CVD) as transparent conductive electrodes (TCE) in organic photovoltaic cells. Graphene films were synthesized by CVD, transferred to transparent substrates, and evaluated in organic solar cell heterojunctions (TCE/poly-3,4-ethylenedioxythiophene:poly styrenesulfonate (PEDOT:PSS)/copper phthalocyanine/fullerene/bathocuproine/aluminum). Key to our success is the continuous nature of the CVD graphene films, which led to minimal surface roughness ( approximately 0.9 nm) and offered sheet resistance down to 230 Omega/sq (at 72% transparency), much lower than stacked graphene flakes at similar transparency. In addition, solar cells with CVD graphene and indium tin oxide (ITO) electrodes were fabricated side-by-side on flexible polyethylene terephthalate (PET) substrates and were confirmed to offer comparable performance, with power conversion efficiencies (eta) of 1.18 and 1.27%, respectively. Furthermore, CVD graphene solar cells demonstrated outstanding capability to operate under bending conditions up to 138 degrees , whereas the ITO-based devices displayed cracks and irreversible failure under bending of 60 degrees . Our work indicates the great potential of CVD graphene films for flexible photovoltaic applications.