Single-junction Photovoltaic Cells Research Articles

First-Principles Calculations of the Structural, Mechanical, Optical, and Electronic Properties of X2Bi4Ti5O18 (X = Pb, Ba, Ca, and Sr) Bismuth-Layered Materials for Photovoltaic Applications

For the first time, density functional theory (DFT) calculations have been employed for the measurement of the structural, mechanical, optical, and electrical properties of a bismuth-layered structure ferroelectrics (BLSFs) family member possessing an orthorhombic structure with Cmc21 space group. Based on the exchange–correlation approximation, our calculations show that Pb2Bi4Ti5O18 possesses an indirect band gap, while the materials X2Bi4Ti5O18 (X = Ba, Ca, and Sr) demonstrate direct band gap, where the estimated density functional fundamental band gap values lie between 1.84 to 2.33 eV, which are ideal for photovoltaic applications. The optical performance of these materials has been investigated by tuning the band gaps. The materials demonstrated outstanding optical characteristics, such as high absorption coefficients and low reflection. They exhibited impressive absorption coefficient (α = 105 cm−1) throughout a broad energy range, especially in the visible spectrum (105 cm−1 region). The findings show that the compounds demonstrate lower reflectivity in the visible and UV regions, making them suitable for single-junction photovoltaic cells and optoelectronic applications. The Voigt–Reuss–Hill averaging technique has been employed to derive elastic parameters like bulk modulus (B), Young’s modulus, shear modulus (G), the Pugh ratio (B/G) and the Frantesvich ratio (G/B) at 0.1 GPa. The mechanical stability of the compounds was analyzed using the Born stability criteria. Pugh’s ratio and Frantesvich’s ratio show that all the compounds are ductile, making them ideal for flexible optical applications.

Tuning the hole transport layer in the Ca3SbI3 absorber-based solar cells to improve the power conversion efficiency

The renewable energy field has been demonstrating a significant deal of interest in lead (Pb)-free inorganic halide perovskites because of their remarkable optical, mechanical, electrical, and structural properties. Investigators have been studying Ca3SbI3-based single junction photovoltaic cells in various layouts, such as an electron transport layer (ETL) constructed of SnS2 and three distinct hole transport layers (HTL) constructed of MoO3, CBTS, and Cu2O. We extensively analyzed various factors using SCAPS-1D simulation software, delving into aspects like the alignment of bands, layer thickness, defect levels, doping levels, interface defects, carrier concentrations, generation, recombination, voltage at the open circuit (VOC), current at the short circuit (JSC), fill factor (FF), and the efficiency of power conversion (PCE) using mathematical methods. The study states that the Cu2O HTL design reached its highest efficiency at 31.65 %, with an open circuit voltage (VOC) of 1.5013 V, a short circuit current (JSC) of 24.036941 mAcm−2, and a fill factor (FF) of 87.71 % and the CBTS HTL setup achieved a slightly lower efficiency of 29.43 %, with a VOC of 1.3946 V, a JSC of 24.05685 mA/cm2, and the value of an FF is 87.71 %. Conversely, the MoO3 HTL design efficiency at 24.7 %, with an open circuit voltage (VOC) of 1.2530 V, a short circuit current (JSC) of 22.846937 mAcm−2, and a fill factor (FF) of 86.29 % These findings offer valuable insights and a practical approach for developing affordable thin-film photovoltaic cells based on Ca3SbI3.

Improving the power conversion efficiency of RbPbBr3 absorber based solar cells through the variation of efficient hole transport layers

Novel rubidium-lead-bromide (RbPbBr3) hybrid perovskite solar cells (HPSCs) are gaining attention from researchers because of their exceptional semiconductor qualities. Researchers have been examining RbPbBr3-based single junction photovoltaic cells in a number of configurations, including two different hole transport layers (HTL) made of V2O5 and MoTe2 and an electron transport layer (ETL) made of CdS. We investigated elements including band alignment, defect density, layer thickness, doping concentration, interface defect density, carrier concentration, generation, recombination, open circuit voltage (VOC), short circuit current (JSC), fill factor (FF), and power conversion efficiency (PCE) through extensive numerical analysis using SCAPS-1D simulation software. According to the research, the V2O5 HTL design, with a VOC of 1.1433 V, a JSC of 34.3969 mAcm−2, and an FF of 86.63 %, attained the maximum PCE at 34.06 %. By contrast, the MoTe2 HTL configuration's PCE was 31.66 %, with a VOC of 1.0388 V, a JSC of 34.4977 mAcm−2, and an FF of 88.35 %. These results provide insightful information and a workable strategy for creating RbPbBr3-based, reasonably priced thin-film solar cells.

Solar power conversion: CuI hole transport layer and Ba3NCl3 absorber enable advanced solar cell technology boosting efficiency over 30.

Researchers are becoming more interested in novel barium-nitride-chloride (Ba3NCl3) hybrid perovskite solar cells (HPSCs) due to their remarkable semiconductor properties. An electron transport layer (ETL) built from TiO2 and a hole transport layer (HTL) made of CuI have been studied in Ba3NCl3-based single junction photovoltaic cells in a variety of variations. Through extensive numerical analysis using SCAPS-1D simulation software, we investigated elements such as layer thickness, defect density, doping concentration, interface defect density, carrier concentration, generation, recombination, temperature, series and shunt resistance, open circuit voltage (V OC), short circuit current (J SC), fill factor (FF), and power conversion efficiency (PCE). The study found that the HTL CuI design reached the highest PCE at 30.47% with a V OC of 1.0649 V, a J SC of 38.2609 mA cm-2, and an FF of 74.78%. These findings offer useful data and a practical plan for producing inexpensive, Ba3NCl3-based thin-film solar cells.

Carrier multiplication in perovskite solar cells with internal quantum efficiency exceeding 100%

Carrier multiplication (CM) holds great promise to break the Shockley-Queisser limit of single junction photovoltaic cells. Despite compelling spectroscopic evidence of strong CM effects in halide perovskites, studies in actual perovskite solar cells (PSCs) are lacking. Herein, we reconcile this knowledge gap using the testbed Cs0.05FA0.5MA0.45Pb0.5Sn0.5I3 system exhibiting efficient CM with a low threshold of 2Eg (~500 nm) and high efficiency of 99.4 ± 0.4%. Robust CM enables an unbiased internal quantum efficiency exceeding 110% and reaching as high as 160% in the best devices. Importantly, our findings inject fresh insights into the complex interplay of various factors (optical and parasitic absorption losses, charge recombination and extraction losses, etc.) undermining CM contributions to the overall performance. Surprisingly, CM effects may already exist in mixed Pb-Sn PSCs but are repressed by its present architecture. A comprehensive redesign of the existing device configuration is needed to leverage CM effects for next-generation PSCs.

Design and optimization of four-terminal mechanically stacked and optically coupled silicon/perovskite tandem solar cells with over 28% efficiency

Silicon/perovskite tandem devices are believed to be a favorite contender for improving cell performance over the theoretical maximum value of single-junction photovoltaic (PV) cells. The present study evaluates the design and optimization of four-terminal (4-T) mechanically stacked and optically coupled configurations using SCAPS (solar cell capacitance simulator). Low-cost, stable, and easily processed semitransparent carbon electrode-based perovskite solar cells (c-PSCs) without hole transport material (HTM) and highly efficient crystalline silicon (c-Si) PV cells were utilized as top and bottom cells, respectively. The wide bandgap multi-cation perovskite Csx(FA0.4MA0.6)1−xPbI2.8Br0.2 and a low bandgap c-Si were employed as light-harvesting layers in the top and bottom cells, respectively. The impact of perovskite thickness and doping concentrations were examined and optimized for both tandem configurations. Under optimized conditions, thicknesses of 1000 nm and 1100 nm are the best values of the perovskite absorber layer for 4-T mechanically stacked and optically coupled arrangements, respectively. Likewise, 1 × 1017 cm−3 doping concentration of top cells revealed the highest performance in both structures. With these optimized parameters under tandem configurations, efficiency values of 28.38% and 29.34% were obtained in 4-T mechanically and optically coupled tandems, respectively. Results suggest that by optimizing perovskite thickness and doping concentration, the proposed designs using HTM-free c-PSCs could enhance device performance.

A first-principles study of the stability, electronic structure, and optical properties of halide double perovskite Rb2Sn1-xTexI6 for solar cell applications.

Owing to their emerging role in solar cell technology, lead halide perovskites have aroused significant research interest in the recent past. However, due to its obvious toxicity, looking for a potential alternative to lead is becoming one of the most important pursuits in present times. We present our work based on density functional theory (DFT) investigating lead free defect perovskites (Rb2Sn1-xTexI6 (0 ≤x≤ 1)). In particular, we explore the crystal structure, thermodynamic stability, electronic structure, and optical properties of Rb2Sn1-xTexI6 (0 ≤x≤ 1) as a function of increasing Te concentration. Our results show that the Sn-Te alloyed perovskites exhibit considerable stability, a suitable band gap, small effective mass, and excellent light absorption. Especially, Rb2Sn0.75Te0.25I6 and Rb2Sn0.50Te0.50I6 have a direct band gap of 1.35 and 1.44 eV, respectively, which is highly favorable for use in a single-junction photovoltaic cell. We hope that our work will arouse the interest of experimental as well as theoretical scientists for synthesizing new materials and/or exploring the Sn-Te mix as a potential substitute for lead in photovoltaic materials.

Synergistic Tandem Solar Electricity-Water Generators

Summary Energy and clean water are two intertwined fundamental elements for human civilization and sustainable development. Here, we devise a monolithic tandem solar electricity-water generator that synergistically produces electricity and clean water by utilizing the full spectrum of solar irradiance. The tandem generator has two components: a top infrared-transparent photovoltaic device using above-band-gap photons, and a bottom solar water purifier using the below-band-gap photons. More strikingly, a well-designed water-proof thermal interconnecting layer (WTIL) makes these two components work synergistically: the bottom purifier serves as an evaporative cooler of the top solar cell to increase its efficiency, whereas the thermalization energy of the top cell is reutilized by the bottom purifier for producing more clean water. We experimentally demonstrate that a prototype hybrid tandem solar device with WTIL can generate electricity with a power output of 204 W m−2 and purify water at a rate of 0.80 kg m−2 h−1 under 1-sun illumination.

Effect of band gap on power conversion efficiency of single-junction semiconductor photovoltaic cells under white light phosphor-based LED illumination

On the basis of the detailed balance principle, curves of efficiency limit of single-junction photovoltaic cells at warm and cool white light phosphor-based LED bulbs with luminous efficacy exceeding 100 lm/W have been simulated. The effect of energy band gap and illuminance on the efficiencies at warm and cool light is discussed. The simulations carried out show that maximum power conversion efficiency at 1000 lx reaches 52.0% for cool light and 53.6% for warm one, while the optimal energy band gap is 1.80 eV and 1.88 eV, respectively. The simulated limits are also referenced to experimental data presented in literature to show that there is still a lot of room for improving indoor photovoltaic cells.

Single junction photovoltaic cell and sub-modules in optimization of solar farms

Turkey has a great potential in terms of renewable energy sources. Particularly, this potential comes to the fore in solar energy. Compared to the rest of Europe and other countries worldwide, Turkey has a very large level of annual sunshine period. One of the main elements used to produce electricity from solar energy in solar farms is solar cells. They produce direct current by converting the solar radiation directly onto the solar energy. In order to increase the power output, several solar cells are connected to each other in parallel or in series and mounted on a surface. This structure is called the solar cell module or photovoltaic module. If necessary, these modules can be connected to each other in series or parallel, to create a series of photovoltaic. For high efficiency photovoltaic cycle, it is necessary to improve the structural and electrical properties of the material to optimize the forbidden energy range and to use the most appropriate combination in the choice of the heterocline. In addition, the fact that the selected material can be produced economically at large scale is one of the conditions and it is desired that the sensitivity to the environment is considered during the use of this material. There are many types of solar cells in the market. Recently, 3rd generation solar cells from different materials have taken their place in the market. In a photovoltaic cell, the key operating parameters are efficiency, area, fill factor, and current-voltage (I-V) characteristics. This study’s aim is determining the photovoltaic performance and comparing the solar cells fabricated in different types according to key operating parameters.

Separating the Heat from the Gap

Increasing the conversion efficiency of incident solar energy to electricity is a key goal in the solar R&D community. In this issue of Joule , a conceptual hybrid photovoltaic/thermal (PV/T) receiver design is reported by the research groups of Evelyn Wang and Gang Chen. High exergetic efficiency is achieved by absorbing below-bandgap and excessively high-energy photons as thermal energy, while allowing photons at the PV's bandgap to pass through to the underlying cell.

Economic viability of thin-film tandem solar modules in the United States

Tandem solar cells are more efficient but more expensive per unit area than established single-junction (SJ) solar cells. To understand when specific tandem architectures should be utilized, we evaluate the cost-effectiveness of different II–VI-based thin-film tandem solar cells and compare them to the SJ subcells. Levelized cost of electricity (LCOE) and energy yield are calculated for four technologies: industrial cadmium telluride and copper indium gallium selenide, and their hypothetical two-terminal (series-connected subcells) and four-terminal (electrically independent subcells) tandems, assuming record SJ quality subcells. Different climatic conditions and scales (residential and utility scale) are considered. We show that, for US residential systems with current balance-of-system costs, the four-terminal tandem has the lowest LCOE because of its superior energy yield, even though it has the highest US$ per watt (US$ W–1) module cost. For utility-scale systems, the lowest LCOE architecture is the cadmium telluride single junction, the lowest US$ W–1 module. The two-terminal tandem requires decreased subcell absorber costs to reach competitiveness over the four-terminal one. Multijunction solar cells are more efficient and more expensive than single-junction photovoltaic cells, but their cost-effectiveness remains unclear. Here, Sofia et al. study the manufacturing costs of thin-film devices to analyse the levelized cost of electricity of single and multijunctions in the United States.

0.5-Gb/s OFDM-Based Laser Data and Power Transfer Using a GaAs Photovoltaic Cell

In this letter, we demonstrate for the first time the additional capability of high-speed data communication for single-junction photovoltaic (PV) cells. A record 3-dB bandwidth of 24.5 MHz is reported for a gallium arsenide (GaAs) PV cell. The PV cell is shown to achieve a power efficiency of at least 42% when irradiance of 0.46 W/cm2 is received from 847-nm vertical-cavity surface-emitted laser. Optimized bit-and-power-loaded optical orthogonal frequency-division multiplexing (OFDM) is applied to use the communication bandwidth most efficiently. With this, a data rate of 0.5 Gb/s is achieved for a 2-m OFDM-based laser link. To the best of our knowledge, the reported data rates achieved with a GaAs PV cell as the detector are the highest for simultaneous optical wireless information and power transfer.

CuO NPs incorporated single and double junction polymer solar cells

Multi-junction architecture is an attractive method to overcome the efficiency limit of single-junction photovoltaic solar cells. Series-connected multi-junction polymer solar cells (PSCs) have attracted much attention during the past decade. In this study, single- and double-layer polymer solar cells were fabricated incorporating copper oxide and zinc oxide nanoparticles (CuO and ZnO NPs) in the active layers. Thermal annealing treatment was applied to the single and double junction devices at 200oC to optimize the nanoscale morphology. The single layer device produced 2.963% power conversion efficiency and it was reduced to 1.102% in the double junction solar cell. However, the enhanced morphological and optoelectronic properties attained by applying thermal annealing, slightly increased the power conversion efficiency. Meanwhile, the external quantum efficiency (EQE) increased from 32.4% to 37%, showing an enhancement of 12.4% with the thermal annealing treatment.

Elucidation of Excitation Energy Dependent Correlated Triplet Pair Formation Pathways in an Endothermic Singlet Fission System.

Singlet fission is the spin-allowed conversion of a photogenerated singlet exciton into two triplet excitons in organic semiconductors, which could enable single-junction photovoltaic cells to break the Shockley-Queisser limit. The conversion of singlets to free triplets is mediated by an intermediate correlated triplet pair (TT) state, but an understanding of how the formation and dissociation of these states depend on energetics and morphology is lacking. In this study, we probe the dynamics of TT states in a model endothermic fission system, TIPS-Tc nanoparticles, which show a mixture of crystalline and disordered regions. We observe the formation of different TT states, with varying yield and different rates of singlet decay, depending on the excitation energy. An emissive TT state is observed to grow in over 1 ns when excited at 480 nm, in contrast to excitation at lower energies where this emissive TT state is not observed. This suggests that the pathway for singlet fission in these nanoparticles is strongly influenced by the initial sub-100 fs relaxation of the photoexcited state away from the Franck-Condon point, with multiple possible TT states. On nanosecond time scales, the TT states are converted to free triplets, which suggests that TT states might diffuse into the disordered regions of the nanoparticles where their breakup to free triplets is favored. The free triplets then decay on μs time scales, despite the confined nature of the system. Our results provide important insights into the mechanism of endothermic singlet fission and the design of nanostructures to harness singlet fission.

New Triplet Sensitization Routes for Photon Upconversion: Thermally Activated Delayed Fluorescence Molecules, Inorganic Nanocrystals, and Singlet-to-Triplet Absorption.

Photon upconversion based on triplet-triplet annihilation (TTA-UC) has attracted much interest because of its possible applications to renewable energy production and biological fields. In particular, the UC of near-infrared (NIR) light to visible (vis) light is imperative to overcome the Shockley-Queisser limit of single-junction photovoltaic cells, and the efficiency of photocatalytic hydrogen production from water can also be improved with the aid of vis-to-ultraviolet (UV) UC. However, both processes have met limitations in the wavelength range, efficiency, and sensitivity for weak incident light. This Account describes recent breakthroughs that solve these major problems, new triplet sensitization routes to significantly enlarge the range of conversion wavelength by minimizing the energy loss during intersystem crossing (ISC) of triplet sensitizers or bypassing the ISC process. The photochemical processes of TTA-UC in general start with the absorption of longer wavelength incident light by triplet sensitizers, which generate the triplet states via ISC. This ISC inevitably accompanies the energy loss of hundreds of millielectronvolts, which significantly limits the TTA-UC with large anti-Stokes shifts. The small S1-T1 gap of molecules showing thermally activated delayed fluorescence (TADF) allows the sensitization of emitters with the highest T1 and S1 energy levels ever employed in TTA-UC, which results in efficient vis-to-UV UC. As alternatives to molecular sensitizers in the NIR region, inorganic nanocrystals with broad NIR absorption bands have recently been shown to work as effective sensitizers for NIR-to-vis TTA-UC. Their small exchange splitting minimizes the energy loss during triplet sensitization. The modification of nanocrystal surfaces with organic acceptors via coordination bonds allows efficient energy transfer between the components and succeeding TTA processes. To remove restrictions on the energy loss during ISC, molecules with direct singlet-to-triplet (S-T) excitation are employed as triplet sensitizers. Although the S-T absorption is spin forbidden, large spin-orbital coupling occurs for appropriately designed metal complexes, which allow S-T absorption in the NIR region with large absorption coefficients. While the triplet lifetime of such S-T absorption sensitizers is often short (less than microsecond), the integration of the molecular sensitizers with emitter assemblies allows facile Dexter energy transfer to the surrounding emitter molecules, leading to efficient NIR-to-vis UC emission through triplet energy migration (TEM) in the condensed state. By judicious modification of the chromophore structures, the first example of NIR-to-blue UC has also been achieved. It is essential to combine these new triplet sensitization routes with an upconverted energy collection (UPCON) approach in molecular assemblies to effectively populate emitter triplets and to overcome remaining issues including back energy transfer. We propose two overall materials designs for the TEM-UPCON strategy, core-shell-shell structures and trilayer structures composed of triplet donor, acceptor, and energy collector. The fusion between triplet science and chemistry of self-assembly would overcome previous difficulties of NIR-to-vis and vis-to-UV TTA-UC toward real-world applications ranging from energy to biology.

Enhancing dye-sensitized solar cell efficiency through broadband near-infrared upconverting nanoparticles.

The inability to utilize near infrared (NIR) light has posed a stringent limitation for the efficiencies of most single-junction photovoltaic cells such as dye-sensitized solar cells (DSSCs). Here, we describe a strategy to alleviate the NIR light harvesting problem by upconverting non-responsive NIR light in a broad spectral range (over 190 nm, 670-860 nm) to narrow solar-cell-responsive visible emissions through incorporated dye-sensitized upconversion nanoparticles (DSUCNPs). Unlike typically reported UCNPs with narrow and low NIR absorption, the organic dyes (IR783) anchored on the DSUCNP surface were able to harvest NIR photons broadly and efficiently, and then transfer the harvested energy to the inorganic UCNPs (typically reported), entailing an efficient visible upconversion. We show that the incorporation of DSUCNPs into the TiO2 photoanode of a DSSC is able to elevate its efficiency from 7.573% to 8.568%, enhancing the power conversion efficiency by about 13.1%. We quantified that among the relative efficiency increase, 7.1% arose from the contribution of broad-band upconversion in DSUCNPs (about ∼3.4 times higher than the highest previously reported value of ∼2.1%), and 6.0% mainly from the scattering effect of DSUCNPs. Our strategy has immediate implications for the use of DSUCNPs to improve the performance of other types of photovoltaic devices.

Spectral splitting optimization for high-efficiency solar photovoltaic and thermal power generation

Utilizing the full solar spectrum is desirable to enhance the conversion efficiency of a solar power generator. In practice, this can be achieved through spectral splitting between multiple converters in parallel. However, it is unclear which wavelength bands should be directed to each converter in order to maximize the efficiency. We developed a model of an ideal hybrid solar converter which utilizes both a single-junction photovoltaic cell and a thermal engine. We determined the limiting efficiencies of this hybrid strategy and the corresponding optimum spectral bandwidth directed to the photovoltaic cell. This optimum width is inversely proportional to the thermal engine efficiency and scales with the bandgap of the photovoltaic cell. This bandwidth was also obtained analytically through an entropy minimization scheme and matches well with our model. We show that the maximum efficiency of the system occurs when it minimizes the spectral entropy generation. This concept can be extended to capture generalized non-idealities to increase the usefulness of this technique for a range of full solar spectrum utilization technologies.

Novel nanostructures for efficient photon upconversion and high-efficiency photovoltaics

Upconversion of low-energy photons theoretically allows the creation of single-junction solar cells with efficiency far above the Shockley-Queisser (SQ) limit. However, the net efficiency gains that can be realized depend critically on details of the upconversion process employed. We define three important metrics of the performance of an upconversion material: upconversion quantum efficiency (UQE), photon energy sacrifice (PES), and absorption bandwidth (AB). We analyze the performance of existing upconversion materials relative to both these metrics and existing computational models of a single-junction photovoltaic (PV) cell backed by an upconverter. Guided by the results of this analysis, we develop a design for new solid state upconversion nanostructures that suppresses the dominant energy loss pathways and can enable substantial improvements in overall solar energy harvesting. We describe and model the performance of a specific realization of this design that uses an InAs quantum dot (QD) and a graded InAlBiAs layer to suppress both radiative and nonradiative loss pathways. We show that this design can be tailored to maximize upconversion efficiency and can enable a practical upconversion-backed PV system to exceed the SQ limit.

Diffractive Spectral-Splitting Optical Element Designed by Adjoint-Based Electromagnetic Optimization and Fabricated by Femtosecond 3D Direct Laser Writing

The greatest source of loss in conventional single-junction photovoltaic cells is their inefficient utilization of the energy contained in the full spectrum of sunlight. To overcome this deficiency, we propose a multijunction system that laterally splits the solar spectrum onto a planar array of single-junction cells with different band gaps. As a first demonstration, we designed, fabricated, and characterized dispersive diffractive optics that spatially separated the visible (360–760 nm) and near-infrared (760–1100 nm) bands of sunlight in the far field. Inverse electromagnetic design was used to optimize the surface texture of the thin diffractive phase element. An optimized thin film fabricated by femtosecond two-photon absorption 3D direct laser writing shows an average splitting ratio of 69.5% between the visible and near-infrared light over the 380–970 nm range at normal incidence. The splitting efficiency is predicted to be 80.4% assuming a structure without fabrication errors. Spectral-splitting a...