Photovoltaic Process Research Articles

High-response heterojunction phototransistor based on vertically grown graphene nanosheets film

Carbon-phototransistor with a structure of vertically grew graphene nanosheets embedded carbon (GNEC) film is fabricated through an electron-assisted sputtering-deposition method. This heterojunction phototransistor of GNEC/n-Si exhibits broad detection range (from 450 nm to 1200 nm), high photoresponsivity (1.298 × 104 A/W), and rapid response to on-off optical signals (4.91 μs). Driven by the source-drain voltage applied to the GNEC film, electrons recycle in the circuit before recombination, which enhance drastically the usage efficiency of photo-induced carriers. Besides, GNEC film contains a large amount of graphene edges, which may serve as electron pump in the photovoltaic process based on the e-h separation in the p-n junction. The GNEC/n-Si phototransistor improves the responsivity of ∼103 order compared with that of photodiode mode.

Study of the open circuit voltage dependence on incident light intensity of planar heterojunction organic solar cell

Organic photovoltaic is an emerging technology employing organic molecules as absorbers has gained tremendous attention in the past two decades due to its potential utilization as a renewable energy source. Contrary to conventional solar cells, excitons are formed under illumination which diffuse towards the heterojunction interface for dissociation into the photo charge-carriers. Heterojunction in the organic photovoltaic devices are formed either by stacking the layers of donor and acceptor molecules or by blending the both. Due to weak van-der Waals interaction between the molecules, intermixed states, in addition to the pure states of donor and acceptor molecules, are formed at the heterojunction interface which affects the electronic process and the power conversion efficiency. Significant efforts have been made to understand the photovoltaic process particularly in the bulk heterojunction solar cells however, least efforts have been devoted to investigate the governing mechanisms in the planner heterojunction solar cells. The motive of this study is to characterize the planar heterojunction solar cells based on the Copper Phthalocyanine (CuPc) and Fullerene (C60) molecules under light illumination. The devices were fabricated under controlled condition in the normal device configuration, ITO (150 nm) |PEDOT:PSS(50 nm)|CuPc(20 nm)|C60(40 nm)|BCP(10 nm)| Ag(80 nm), and characterized performing the light intensity dependent measurement in the wide illumination range. The solar cell parameters such as open circuit voltage, short circuit current and the power conversion efficiency have been discussed as a function of illumination intensity in the wider illumination range.

Effect of Temperature on the Performance of Photovoltaic Module

Metrological parameters plays significant role on the performance of solar panels in electrical power generation. To ascertain the extent to which ambient temperature, temperature of the panels, solar radiation were measured, recorded and analyzed at half-hour interval for five days, at the same period two solar panels were subjected to test, one being connected to a system of cooling leaving the other untouched. Measurement of both the output current and voltage were made from which the power output was calculated. The result shows that the power output was increasing as the solar radiation increased, which is clear indication that the entire photovoltaic process depend on the radiation intensity and environmental conditions. It was also observed that the efficiency of the solar panel with cooling system is slightly greater than that without cooling system. The efficiency and energy output of both solar panels were determined to be 15%, 13% and 477kWh, 449kWh respectively. The difference of 28kWh is not supposed to be neglected, because considering the difference of many days and many panels cannot be neglected. Also few approaches that have been proposed to reduce the effect of temperature on the solar photovoltaic system by choosing the appropriate configurations, by mounted on free standing frames, photovoltaic thermal collectors and building integrated photovoltaic arrays, respectively

Photovoltaic Control of Ferromagnetism for Flexible Spintronics.

The demand for low-power flexible spintronics for sensing, communicating, and data processing applications boosts an intense search for novel ways of controlling magnetism. In this work, a photovoltaic controllable flexible spintronic device within a Kapton/Ta/Co/(PC71BM/PTB7-Th)/Pt heterostructure was demonstrated, and the magnetic anisotropy change of this flexible heterostructure as a function of the external light radiation and strain was quantitatively determined. 150 mW/cm2 white light illumination induced 489 Oe out-of-plane ferromagnetic resonance field modulation, which was attributed to the photogenerated electron doping in the cobalt film. The chemical contamination effect and the interfacial oxidation effect during the photovoltaic doping process were eliminated. Moreover, it was found that the working function of the thin-film electrodes were different from the bulk values via an ultraviolet photoelectron spectroscopy test. Our results on flexible photovoltaic spintronics systems will invigorate the research toward the development of solar-driven energy-efficient spintronics.

Photovoltaic Response and Charge Redistribution Processes in GaAs/AlGaAs Multiple‐Quantum Wells Structure

The impact of radiative and non‐radiative processes on the photovoltaic response of GaAs/AlGaAs multiple‐quantum wells is investigated by temperature, excitation power, and chopping‐frequency‐dependent surface photovoltage (SPV) measurements. It is shown that a systematic study of SPV amplitude along with phase spectra can provide important information on thermal escape, carrier localization, and spatial redistribution of charge carriers. Characteristic features in SPV‐phase spectra related to quantum well (QW) transitions and their variation under an external perturbation are explained by the electron–electron interaction. It is found that a many‐body interaction inside the QW is responsible for the capture of charges at the heterointerfaces, which builds up an interface electric field and hinders the drift/diffusion of charges. Such an effect becomes dominant under higher excitation powers, causing a sub‐linear enhancement of photovoltage amplitude and an increase in phase delay as a function of photon flux. From the chopping‐frequency‐dependent SPV measurements, it is concluded that carriers during the drift in barrier layers are repeatedly captured by point defects and other QWs, which enhances the effective time response of the photovoltage signal. Results obtained in this study are beneficial in the engineering of quantum structures for high‐efficiency photovoltaics and non‐invasive characterization of electro‐optical processes.

Enhanced Charge Transfer in Atom‐Thick 2H–WS2 Nanosheets’ Electron Transport Layers of Perovskite Solar Cells

The structure and the electronic properties of the electron‐transport layer (ETL) of perovskite solar cells (PSCs) govern the interfacial charge transfer and charge transportation to the electrode. The ETLs of two dimensions, that are atom thick, and have a planar structure that possesses special electronic properties, such as the surface collective motion of excitons or charge transfer–driven defect state relief, that is 2D transition metal dichalcogenide, allow a highly energetic carrier dynamic process for enhanced photovoltaic effect. Herein, it is discovered that planar, few‐atom‐thick 2H–WS2 nanosheets' ETLs drive ultrafast charge transfer and transportation along the ETL during the photovoltaic process. Time‐resolved photoluminescence and electrochemical impedance spectroscopy analysis results indicate that the charge transfer from the perovskite to the ETL occurs as fast as 5.9 ns with charge transfer resistance as low as 25.6 Ω. This allows the PSC device to produce a power conversion efficiency of 18.21% with short‐circuit current density, open‐circuit voltage, and fill factor as high as 22.24 mA cm2, 1.12 V, and 0.731, respectively. The PSC retains 96.87% of its performance when being aged in nitrogen atmosphere for 33 days. Atom‐thick planar WS2 ETL nanosheets can be the basis for the development of high‐performance PSC devices.

Long-Lived Hot Electron in a Metallic Particle for Plasmonics and Catalysis: Ab Initio Nonadiabatic Molecular Dynamics with Machine Learning.

Multiple experiments provide evidence for photovoltaic, catalytic, optoelectronic, and plasmonic processes involving hot, i.e., high energy, electrons in nanoscale materials. However, the mechanisms of such processes remain elusive, because electrons rapidly lose energy by relaxation through dense manifolds of states. We demonstrate a long-lived hot electron state in a Pt nanocluster adsorbed on the MoS2 substrate. For this purpose, we develop a simulation technique, combining classical molecular dynamics based on machine learning potentials with ab initio nonadiabatic molecular dynamics and real-time time-dependent density functional theory. Choosing Pt20/MoS2 as a prototypical system, we find frequent shifting of a top atom in the Pt particle occurring on a 50 ps time scale. The distortion breaks particle symmetry and creates unsaturated chemical bonds. The lifetime of the localized state associated with the broken bonds is enhanced by a factor of 3. Hot electrons aggregate near the shifted atom and form a catalytic reaction center. Our findings prove that distortion of even a single atom can have important implications for nanoscale catalysis and plasmonics and provide insights for utilizing machine learning potentials to accelerate ab initio investigations of excited state dynamics in condensed matter systems.

The Use of Lasers at Various Stages of the Manufacturing Process of Solar Cells Based on Crystalline Silicon

The purpose of this chapter of the book is to present knowledge on the use of laser technology in silicon photovoltaic cell manufacturing processes. Particular consideration was given to the technique of using a disk laser to cut the edges of silicon wafers together with the recognition of the flow of laser micromachining on the quality of cut edges to obtain their minimal deformation. The second topic described is the method of producing point contacts employing laser radiation between a layer of vaporised aluminium and crystalline silicon using the Nd:YAG laser. The results illustrating the impact of the structure and parameters of point contact for a given laser radiation energy on basic electrical parameters for complete, prototype solar cells are included. The chapter in the book provides an overview of the literature on the above topics and presents selected results of experimental works carried out by the authors. The motive for its publication is the need to present selected results of own research carried out in the Welding Department cooperating for many years with the Institute of Engineering and Biomedical Materials (IMIiB) of the Silesian University of Technology and the Institute of Metallurgy and Materials Engineering (IMIM) of the Polish Academy of Sciences in Cracow.

Transition from Doublet to Triplet Excitons in Single Perovskite Nanocrystals.

Lead halide perovskite nanocrystals (NCs) have emerged as novel semiconductor nanostructures possessing great potential for optoelectronic, photovoltaic, and quantum information processing applications. Success in these applications requires a comprehensive understanding of the perovskite NCs' electronic structures, which mysteriously exhibit either doublet or triplet peaks of exciton luminescence at the single-particle level. Here we show that the transition from doublet- to triplet-exciton peaks can be triggered in single CsPbI3 NCs from the same batch of samples when they are stored in the ambient environment. We propose theoretically that the doublet-exciton peaks originate from two in-plane dipole moments, while the optical transition arising from the out-of-plane dipole moment becomes prominent only after the crystal-field splitting is strongly reduced by the structural transformation in the deterioration process. Furthermore, the quantum-confinement effect is strongly reinforced in the single CsPbI3 NCs with a triplet-exciton configuration, leading to enhanced Auger recombination and allowing us to extract the emission-energy dependence of the exciton-energy-level fine structure.

1064 nm InGaAsP multi-junction laser power converters

Laser photovoltaic devices converting 1064 nm light energy into electric energy present a promising prospect in wireless energy transmission due to the commercial availability of high power 1064 nm lasers with very small divergence. Besides their high conversion efficiency, a high output voltage is also expected in a laser energy transmission system. Meanwhile, 1064 nm InGaAsP multi-junction laser power converters have been developed using p+-InGaAs/n+-InGaAs tunnel junctions to connect sub-cells in series to obtain a high output voltage. The triple-junction laser power converter structures are grown on p-type InP substrates by metal-organic chemical vapor deposition (MOCVD), and InGaAsP laser power converters are fabricated by conventional photovoltaic device processing. The room-temperature I–V measurements show that the 1 × 1 cm2 triple-junction InGaAsP laser power converters demonstrate a conversion efficiency of 32.6% at a power density of 1.1 W/cm2, with an open-circuit voltage of 2.16 V and a fill factor of 0.74. In this paper, the characteristics of the laser power converters are analyzed and ways to improve the conversion efficiency are discussed.

Energy Loss in Organic Solar Cells: Mechanisms, Strategies, and Prospects

Compared with conventional inorganic solar cells (ISCs), energy loss (Eloss) in organic solar cells (OSCs) is usually much higher, limiting their maximum achievable power conversion efficiency (PCE). In view of this, a hot topic in OSC research is how to make Eloss as low as possible. To date, in some typical organic donor/acceptor (D/A) blends, although Eloss has been reduced to the values comparable with those in ISCs, the PCEs of the corresponding devices still fails to meet expectations. One crucial issue is that the physics behind the photovoltaic process in these D/A blends and the corresponding energy loss remain unclear. Herein, combining with an analysis of the photovoltaic process in OSCs, the mechanisms of different energy loss pathways are first discussed. On this basis, the recent advances focusing on Eloss are systematically summarized according to different strategies: 1) optimizing the energy offset of the D/A blend; 2) optimizing the morphology of the D/A blend; 3) ternary modulation; and 4) spin modulation. Finally, the summary and prospects are presented, where some fundamental questions to be cleared up in the photovoltaic process are proposed, such that more targeted photovoltaic design can be carried out in the future investigations of OSCs.

Direct Dynamic Evidence of Charge Separation in a Dye‐Sensitized Solar Cell Obtained under Operando Conditions by Raman Spectroscopy

AbstractInterfaces play an important role in enhancing the energy conversion performance of dye‐sensitized solar cells (DSCs). The interface effects have been studied by many techniques, but most of the studies only focused on one part of a DSC, rather than on a complete solar cell. Hence, monitoring the interface evolution of a DSC is still very challenging. Here, in situ/operando resonance Raman (RR) spectroscopic analyses were carried out to monitor the dynamics of the photovoltaic conversion processes in a DSC. We observed the creation of new species (i.e., polyiodide and iodine aggregates) in the photosensitization process. We also obtained molecular‐scale dynamic evidence that the bands from the C=C and C=N bonds of 2,2′‐bipyridyl (bpy), the S=C=N bonds of the NCS ligand, and photochemical products undergo reasonably strong intensity and frequency changes, which clearly demonstrates that they are involved in charge separation. Furthermore, RR spectroscopy can also be used to quickly evaluate the performance of DSCs.

Direct Dynamic Evidence of Charge Separation in a Dye-Sensitized Solar Cell Obtained under Operando Conditions by Raman Spectroscopy.

Interfaces play an important role in enhancing the energy conversion performance of dye-sensitized solar cells (DSCs). The interface effects have been studied by many techniques, but most of the studies only focused on one part of a DSC, rather than on a complete solar cell. Hence, monitoring the interface evolution of a DSC is still very challenging. Here, in situ/operando resonance Raman (RR) spectroscopic analyses were carried out to monitor the dynamics of the photovoltaic conversion processes in a DSC. We observed the creation of new species (i.e., polyiodide and iodine aggregates) in the photosensitization process. We also obtained molecular-scale dynamic evidence that the bands from the C=C and C=N bonds of 2,2'-bipyridyl (bpy), the S=C=N bonds of the NCS ligand, and photochemical products undergo reasonably strong intensity and frequency changes, which clearly demonstrates that they are involved in charge separation. Furthermore, RR spectroscopy can also be used to quickly evaluate the performance of DSCs.

TiN@TiO2Core–Shell Nanoparticles as Plasmon‐Enhanced Photosensitizers: The Role of Hot Electron Injection

AbstractMetal–semiconductor heterostructures have attracted a lot of attention due to their ability to enhance photovoltaic and photocatalytic processes via plasmonic effects. Thus far, most of the proposed heterostructures are designed with noble metals and the potential of alternative plasmonic materials, such as titanium nitride (TiN), is not yet well explored. In this work, TiN@TiO2core–shell nanoparticles (NPs) are synthesized and proposed as plasmon‐enhanced photosensitizers for efficient singlet oxygen generation, with the focus on the role of hot electron injection. Excitation of dilute TiN@TiO2NP dispersions by a 700 nm femtosecond‐pulsed laser effectively converts ground‐state oxygen into singlet oxygen (1O2), driven primarily by hot electrons generated during plasmon decay at the TiN–TiO2interface and injected into the TiO2layer. Analytical calculations reveal the unique advantages of TiN–TiO2heterostructures in hot‐electron‐mediated photocatalysis. Considering the chemical inertness and low cost of TiN, TiN@TiO2NPs hold great potential as plasmonic photosensitizers for photodynamic therapy and other photocatalytic applications at red‐to‐near‐infrared wavelengths.

Rational Design of Reversible Redox Shuttle for Highly Efficient Light-Driven Microswimmer.

The light-driven micro/nanomotor (LMNM) is machinery that harvests photon energy and generates self-propulsion in varieties of liquid media. Though visions are made that these tiny swimming machines can serve future medicine for accurate drug delivery and noninvasive microsurgery, their biomedical application is still impeded by the insufficient propulsion efficiency. Here we provide a holistic model of LMNM by considering (i) photovoltaic, (ii) electrochemical, and (iii) electrokinetic processes therein. Such a quantitative model revealed the pivotal role of reaction kinetics and diffusion properties of shuttle ions in the propulsion efficiency of LMNM. With the guidance of this model, a group of ferrocene-based reversible redox shuttles, which generate slow-diffusion ions, was identified, showcasing a high locomotion velocity of ∼500 μm/s (∼100 body length per second) at an ultralow concentration (70 μM). Owing to the in-depth understanding of the fundamental energy conversion processes in LMNM, we anticipate that the development of other high-performance supporting chemicals and LMNM systems will be greatly motivated, foreseeing the advent of LMNM systems with superior efficiency.

Effects of 1,8-diiodooctane on ultrafast charge carrier dynamics and photovoltaic performance in organic solar cells: A comparison of PC71BM and nonfullerene acceptor IT-M

Abstract Nonfullerene acceptors are currently dominating the research and development of organic photovoltaics (OPVs). Exploring the charge separation mechanism is helpful to understand the photovoltaic process in efficient nonfullerene-based OPVs. Herein, we have selected two typical acceptors: PC71BM and nonfullerene acceptor IT-M, and have studied the device function and the ultrafast charge carrier dynamics in the PBDB-TF:IT-M and PBDB-TF:PC71BM blends to investigate how they are affected by different blend morphologies induced by using a popular solvent additive 1,8-diiodooctane (DIO). It is found that ultrafast charge generation occurs in both of the two blend systems. For the IT-M blend film, the DIO additive strongly affects the ultrafast photophysical process. Efficient hole transfer is observed for the IT-M blend processed with DIO compared to the pristine IT-M blend. Moreover, the charge density is significantly increased in the DIO-processed IT-M blend film. In contrast to the IT-M blend, the DIO does not strongly affect the ultrafast charge carrier dynamics in PC71BM blend possibly due to its slight effect on the blend morphology. The reionization of spin-triplet charge transfer states can occur faster than relaxation to triplet in both of the well-ordered blend film processed with DIO resulting in an enhanced current density and fill factor.

Dependence of PV Module Temperature on Incident Time-Dependent Solar Spectrum

The operating temperature of photovoltaic (PV) modules affects the photovoltaic conversion process. The operating temperature depends on various environmental conditions and on material-dependent properties of the PV modules. Many expressions for the operating temperature have been proposed in the literatures, some are simplified working Equation as NOCT (Nominal Operating Cell Temperature), and others are more complex, being based on a combination of the energy balance Equation and NOCT. The present study offers a new approach (model) for determining the PV module temperature based on the energy balance Equation and on the solar spectrum irradiance. While using the new model, the operating temperature has been determined for four module technologies: c-Si, a-Si/ μ c-Si, CdTe, and CIGS and it shows that the operating temperatures for the different cell types are close to the manufacturers’ NOCT data-sheet temperatures. For c-Si technology, for example, the simulation resulted in 43.2° and 46° for the spectrum and NOCT models, respectively. The proposed new model offers a new approach for determining the operating temperature of PV modules.

Photovoltaic properties of the flavonoid‐based photosensitizers: Molecular‐scale perspective on the natural dye solar cells

AbstractThe molecular modification and the effects of the gas and water media on the ability of some flavonoids as the photosensitizers in the natural dye‐sensitized solar cells were theoretically investigated. According to the results, water increases the electrophilicity of the dyes and weakens the dye/TiO2 coupling, prohibiting the electron injection toward TiO2. A longer path for charge transfer and a less electron‐hole overlap for dihydroxychromens elevate the electron transfer more efficient than trihydroxychromen‐based flavonoids. However, the presence of water molecules within an increment in the OH groups in the flavonoid structures improves their spectroscopic properties, which is related to decrement in the gap of the frontier molecular orbitals and increment in the oscillator strength. Also, such favorable structural effects and influence of the water medium on the polarizability and excited‐state lifetime have emerged. According to the energy conversion efficiency, water is a favorable solvent for dihydroxychromen‐based flavonoids. Finally, different analyses on the structural geometries, excited‐state, lifetime within the kinetics, and dynamics of the photovoltaic processes were performed and discussed.

A concentrating solar power system integrated photovoltaic and mid-temperature solar thermochemical processes

The approach of cascading solar energy utilization provides access to reliable and ample supplies of energy and has thus attracted widespread attention. Currently, the hybridization of a concentrating solar photovoltaic process and a solar thermochemical process is a promising approach. This paper describes and investigates a concentrating solar power system to harvest solar energy. Co-producing photovoltaic electricity and solar thermal fuel is its attractive distinction. The visible spectrum is cast onto concentrating photovoltaics to generate electricity, and the ultraviolet and infrared spectra are used to drive methanol decomposition at approximately 250 °C. A spectral splitting parabolic trough concentrator is developed in which incident solar radiation is first split and then concentrated. Based on the measured optical data of concentrators, photovoltaics and reactor, the solar-to-electricity performance is evaluated in the proposed system. The results show that a satisfied solar-to-electricity efficiency of approximately 31.8% would be realized if monocrystalline silicon photovoltaics is adopted. In comparison to individual systems, the efficiency enhancements of about 15.3% and 6.3% are obtained. The solar-to-electricity efficiency can reach approximately 35.1% by adopting gallium arsenide. Meanwhile, the improved optical performance proves that the approach of first splitting and then concentrating sunlight is feasible and promising. Finally, the results are anticipated to lead to a new approach for improving full-spectrum solar energy utilization and guiding the establishment of a prototype in the near future.

Thermal behavior analysis of different solar PV modules via thermographic imaging

The temperature of a photovoltaic (PV) system is a critical factor in the photovoltaic conversion process; hence, the practical performance of a PV system significantly depends on its temperature. Several different methods exist for the determination of PV module temperature. In this study, thermography was employed to investigate the thermal behavior of different solar PV modules under outdoor operating conditions. It was observed that the temperature difference across the area of a PV module could reach as high as 12.5–14.8 °C depending on the type of PV module. Hence, the trends for the lowest and highest temperature were not predictable. Glass-to-glass non-frame PV modules exhibited the highest temperature gradients compared to glass-to-Tedlar non-frame modules. The observed temperature gradients demonstrated that measuring the temperature at a single point on the module was not sufficient to accurately represent the temperature over the entirety of the PV module.