Solar Cell Materials Research Articles

A Pyrrole Modified 3,4-Propylenedioxythiophene Conjugated Polymer as Hole Transport Layer for Efficient and Stable Perovskite Solar Cells.

Despite the outstanding electric properties and cost-effectiveness of poly(3,4-ethylenedioxythiophene) (PEDOT) and its derivatives, their performance as hole transport layer (HTL) materials in conventional perovskite solar cells (PSCs) has lagged behind that of widely used spirobifluorene-based molecules or poly(triaryl amine). This gap is mainly from their poor solubility and energy alignment mismatch. In this work, the design and synthesis of a pyrrole-modified HTL (PPr) based on 3,4-propylenedioxythiophene (ProDOT) are presented for efficient and stable PSCs. As a result of the superior defects passivation ability, excellent contact with perovskite, enhanced hole extraction, and high hydrophobicity, the unencapsulated PPr-based PSCs showed the peak PCE of 21.49% and outstanding moisture stability (over 4000 h). This work highlights the potential application of ProDOT-based materials as HTL for PSCs and underscores the importance of the rational design of PEDOT and its derivatives.

Rapid Thermal-Driven Crystal Growth and Defect Suppression in Antimony Selenide Thin Film for Efficient Solar Cells.

Antimony selenide (Sb2Se3) has demonstrated considerable potential and advancement as a light-absorbing material for thin-film solar cells owing to its exceptional optoelectronic characteristics. However, challenges persist in the crystal growth, particularly regarding the nucleation mechanism during pre-selenization process for Sb2Se3. The defects originating from this process significantly impact the quality of the absorber layer, leading to the degradation in the power conversion efficiency (PCE) of the device. Herein, the evolution of pre-selenization using rapid thermal processing (RTP) on the crystallization quality of Sb2Se3 film is systematically investigated. By optimizing the initial nucleation process during pre-selenization, resulting in a reduction of grain boundaries and nucleation centers, the Sb2Se3 thin films demonstrate enhanced crystallinity and pinholes-free morphology. It is found that the improved quality of the grain interior and interfaces of the Sb2Se3 absorber can mitigate intrinsic defects within the bulk layer, and passivate interfacial defect recombination. As a result, the short circuit current density (JSC) is elevated to 28.97mA cm-2, and a competitive efficiency of 9.03% is achieved in Sb2Se3 device. This study provides comprehensive insight into the process of crystal growth and the mechanism for defect suppression, which holds guiding significance for advancing photovoltaic performance.

Surface Reaction Induced Compressive Strain for Stable Inorganic Perovskite Solar Cells

AbstractCesium‐based inorganic perovskites have emerged as promising light‐harvesting materials for perovskite solar cells (PSCs) due to their promising thermal‐ and photo‐stability. However, obstacles to commercialization remain regarding their phase instability. In this work, we report a facile and effective strategy to regulate the surface compressive strain via in situ surface reaction to stabilize CsPbI3 perovskite. The use of a chelating ligand with a molecular configuration closely matching the integer multiples of the unit cell lattice parameters of CsPbI3 induces compressive strain at the surface of CsPbI3. The chemical bonding and strain modulation synergistically not only passivate film defects, but also inhibit perovskite phase degradation, thus significantly improving the intrinsic stability of inorganic perovskite. Consequently, enhanced power conversion efficiency (PCE) of 21.0 % and 18.6 % were respectively achieved in 0.16‐cm2 lab‐scale devices and 25.3‐cm2 solar modules. Further, surface reaction enables PSCs with enhanced thermal and operational stability; these devices retain over 95 % of their initial PCE after damp‐heat tests (i.e., in 85 °C and 85 % R. H. air) for 2000 h, and remain 99 % of their initial PCE after operating for 2000 h, representing one of the most stable inorganic PSCs reported so far.

Influence of Substrate on Sb2Se3/CdS Heterojunction Thin Film Solar Cells and Evaluation of Their Performance by Dark J‐V Analysis

ABSTRACTA simple binary antimony selenide (Sb2Se3) absorber is evolving as an alternative photovoltaic material in thin film solar cells because of its unique properties and easy processing. Sb2Se3 thin films having good crystalline quality are grown via versatile thermal evaporation from pre‐synthesized near stoichiometric compound material on molybdenum‐coated soda lime glass (SLG) and borosilicate glass (BG) substrates. Following the systematic characterizations on the absorber films, substrate configured Sb2Se3/CdS heterojunction devices were fabricated and their photovoltaic characteristics have been studied using current density vs. voltage (J‐V), dark J‐V modeling, external quantum efficiency and capacitance vs. voltage measurements. The power conservation efficiency values of 4.88% and 5.04% were achieved for the devices fabricated on SLG and BG substrates, respectively with deficit in open circuit voltage. The obtained values are higher in comparison to the reported device efficiencies in substrate configured Sb2Se3 solar cells, in which the absorber is prepared through thermal evaporation. To understand the loss in open circuit voltage, a compact equivalent circuit model was considered and identified the contribution of different shunt leakage paths in the devices. In addition to that, the device fabricated on the SLG was stable with minimal changes in its photovoltaic performance for a period spanning over 200 days. The results obtained are encouraging with scope for improving the device performance through interface engineering and back surface passivation strategies.

2D layered halide perovskite for field-effect transistors

Field-effect transistors are crucial components for modern electronics, generating significant research and profitable interest. Metal halide perovskites have recently emerged as a pioneering active material in solar cells, generating interest in their potential use in other electronic and (opto)electronic devices, including field-effect transistors and phototransistors. However, before they can be commercialized, they still face significant challenges owing to their immanent instabilities with respect to heat, moisture, and light. In contrast, due to their exceptional environmental stability, the newly emerging two-dimensional Ruddlesden–Popper type perovskites have garnered significant recognition. The current state of the field is covered in this review article, as are the problems, and a perspective for the scenarios of perovskite field-effect transistors. The effects of temperature, light, and measurement conditions are taken into account, as well as the physics of the device and the fundamental mechanisms that drive these devices, such as ion migration and ionic defects. Subsequently, the performance of perovskite transistors and phototransistors described so far is analyzed and critically evaluated. Finally, the major roadblocks to perovskite transistor advancement are identified and explored. The lessons learned from other perovskite optoelectronic devices are investigated in order to address these obstacles and bring these devices closer to industrial implementation.

Structurally Compact Penta(N,N-diphenylamino)corannulene as Dopant-free Hole Transport Materials for Stable and Efficient Perovskite Solar Cells.

Hole transport materials (HTMs) are essential for improving the stability and efficiency of perovskite solar cells (PSCs). In this study, we have designed and synthesized a novel organic small molecule HTM, cor-(DPA)5, characterized by a bowl-shaped core with symmetric five diphenylamine groups. Compared to already-known HTMs, the bowl-shaped and relatively compact structure of cor-(DPA)5 facilitates intermolecular π-π interactions, promotes film formations, and enhances charge transport. Consequently, the cor-[DPA(2)]5 HTM exhibits high charge mobility, exceptional hydrophobicity, and a significantly elevated glass transition temperature. Superior to previously reported HTMs such as spiro-OMeTAD and cor-OMePTPA, our newly synthesized cor-(DPA)5 HTM is free from any ionic dopants. As a result, the dopant-free cor-[DPA(2)]5-based PSC demonstrates an impressive efficiency of 24.01%, and exhibits outstanding operational stability. It retains 96% after continuous exposure to 1 sun irradiation for 800 hours under MPP (maximum power point) tracking in ambient air. These findings present a structurally compact novel HTM and exemplify a new approach to the molecular design of HTM for the development of stable and effective PSCs.

Structurally Compact Penta(N,N‐diphenylamino)corannulene as Dopant‐free Hole Transport Materials for Stable and Efficient Perovskite Solar Cells

Hole transport materials (HTMs) are essential for improving the stability and efficiency of perovskite solar cells (PSCs). In this study, we have designed and synthesized a novel organic small molecule HTM, cor‐(DPA)5, characterized by a bowl‐shaped core with symmetric five diphenylamine groups. Compared to already‐known HTMs, the bowl‐shaped and relatively compact structure of cor‐(DPA)5 facilitates intermolecular π–π interactions, promotes film formations, and enhances charge transport. Consequently, the cor‐[DPA(2)]5 HTM exhibits high charge mobility, exceptional hydrophobicity, and a significantly elevated glass transition temperature. Superior to previously reported HTMs such as spiro‐OMeTAD and cor‐OMePTPA, our newly synthesized cor‐(DPA)5 HTM is free from any ionic dopants. As a result, the dopant‐free cor‐[DPA(2)]5‐based PSC demonstrates an impressive efficiency of 24.01%, and exhibits outstanding operational stability. It retains 96% after continuous exposure to 1 sun irradiation for 800 hours under MPP (maximum power point) tracking in ambient air. These findings present a structurally compact novel HTM and exemplify a new approach to the molecular design of HTM for the development of stable and effective PSCs.

Optimization of Sr3NCl3-based perovskite solar cell performance through the comparison of different electron and hole transport layers

Strontium Nitride Trichloride (Sr3NCl3) is a promising absorber material for solar cells due to its unique structural, electrical, and optical properties. We conducted a thorough investigation to scrutinize the structural, optical, and electronic characteristics and the photovoltaic efficiency of double-heterojunction solar cells utilizing Sr3NCl3 absorbers. Various metals were evaluated for the front and rear contacts to determine the optimal metal-semiconductor interface, with the study determining that silver (Ag) is the most suitable option for the front contact and nickel (Ni) for the back contact. The PV performance of innovative Sr3NCl3 absorber-based cell structures was evaluated with two different Hole Transport Layers (HTLs), MASnBe3 and CBTS, alongside ZnO and WS2 serving as the transition metal dichalcogenide (TMD) Electron Transport Layers (ETLs). This investigation examined a range of factors, such as layer thickness, operational temperature, doping density, defect densities at both the interfaces and within the bulk, carrier generation and recombination rates, quantum efficiency (QE), series versus shunt resistance, absorption coefficient, and current density-voltage (J-V) characteristics, utilizing the SCAPS-1D simulator software. Fine-tuning of both two HTL and ETL revealed that the highest power conversion efficiency (PCE) of 27.34 % with JSC of 19.78 mA/cm2, fill factor (FF) of 88.84 %, and VOC of 1.56 V was achieved with MASnBe3 HTL and ZnO ETL, while the lowest PCE of 25.55 %, with JSC of 19.77 mA/cm2, FF of 89.07 %, and VOC of 1.45 V was obtained for CBTS HTL and WS2 ETL, respectively. These findings highlight the promising potential of Sr3NCl3 absorbers with ZnO as ETL and MASnBe3 as HTL for developing advanced perovskites heterostructure solar cells for enhanced performance in the future.

On the absorption coefficient of GaP1-xNx layers and its potential application for silicon photovoltaics

The absorption coefficient and the energy gap of GaP1-xNx layers has been obtained by spectroscopic ellipsometry for samples grown on Si(001) substrates by chemical beam epitaxy with N mole fractions in the range 0 ≤ x ≤ 0.081. The resulting absorption spectra exhibit a direct band-like behavior near the absorption edge. The absorption coefficient values increase with the N content, reaching values in the range α ∼ 1-2x104 cm−1 in the vicinity of the absorption edge below the original GaP direct bandgap, which are comparable to those obtained for high efficiency solar cell materials. Furthermore, dependence of the absorption coefficient with increasing N content points to a strong GaP Γ-like character of the conduction-band wave function of GaP1-xNx alloys near the Brillouin zone center at k = 0, as predicted by the band anticrossing model. Bandgap energy values obtained by spectroscopic ellipsometry are compared with previous values obtained by photoluminescence measurements on the same samples, observing a shift of about 50–100 meV. Finally, the value of the band anticrossing parameter coupling the N level and the host GaP conduction band has been obtained from the dependence of both, the bandgap and the absorption coefficient, with the N content (2.1 and 3.3 eV respectively).

A-Site Engineering with Thiophene-Based Ammonium for High-Efficiency 2D/3D Tin Halide Perovskite Solar Cells.

TTin halide perovskites are the most promising candidate materials for lead-free perovskite solar cells (PSCs) thanks to their low toxicity and ideal bandgap energies. The introduction of 2D/3D mixed perovskite phases in tin-based PSCs (TPSCs) has proven to be the most effective approach to improving device efficiency and stability. However, a 2D perovskite phase normally shows relatively low carrier mobility, which will be unfavorable for carrier transfer in the devices. In this work, we used a thiophene-based cation 2-(thiophen-3-yl)ethan-1-aminium (3-TEA) as a spacer to form a novel 2D perovskite phase in TPSCs, which shows the most promising effect on the performance enhancement in comparison with other cations like 2-(thiophen-2-yl)ethan-1-aminium (2-TEA) and benzene-based 2-phenylethan-1-aminium (PEA). Theoretical calculations reveal that 3-TEA enables the most compact crystal packing of [SnI6]4- octahedral layers, resulting in the lowest hole effective mass and formation energy in the 2D phase. This effect significantly enhances device efficiency and stability by facilitating more efficient carrier transfer within the 2D phase. These findings indicate that thiophene-based 2D perovskites are well-suited for high-performance TPSCs.

Quasi-Planar Core Based Spiro-Type Hole-Transporting Material for Dopant-Free Perovskite Solar Cells.

Hole-transporting material (HTMs) are crucial for obtaining the stability and high efficiency of perovskite solar cells (PSCs). However, the current state-of-the-art n-i-p PSCs relied on the use of 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) exhibit inferior intrinsic and ambient stability due to the p-dopant and hydrophilic Li-TFSI additive. In this study, a new spiro-type HTM with a critical quasi-planar core (Z-W-03) is developed to improve both the thermal and ambient stability of PSCs. The results suggest that the planar carbazole structure effectively passivates the trap states compared to the triphenylamine with a propeller-like conformation in spiro-OMeTAD. This passivation effect leads to the shallower trap states when the quasi-planar HTMs interact with the Pb-dimer. Consequently, the device using Z-W-03 achieves a higher Voc of 1.178 V compared to the spiro-OMeTAD's 1.155 V, resulting in an enhanced efficiency of 24.02 %. In addition, the double-column π-π stacking of Z-W-03 results in high hole mobility (~10-4 cm2 V-1 s-1) even without p-dopant. Moreover, when the surface interface is modified, the undoped Z-W-03 device can achieve an efficiency of nearly 23 %. Compared to the PSCs using spiro-OMeTAD, those with Z-W-03 exhibit enhanced stability under N2 and ambient conditions. This superior performance is attributed to the quasi-planar core structure and the presence of multiple CH/π and π-π intermolecular stacking in Z-W-03. The multiple CH/π and π-π intermolecular contacts of HTMs can improve the hole hopping transport. Therefore, it is imperative to focus on further molecular structure design and optimization of spiro-type HTMs incorporating quasi-planar cores and carbazole moieties for the commercialization of PSCs.

2D g-C3N5 p-Doping of Donor Material for High-Efficiency Organic Solar Cells.

Molecular doping of organic semiconductor is a great strategy for significantly regulating the electronic band structure of organic semiconductor while increasing charge mobility and carrier concentration. Here, a facile strategy is presented by introducing 2D g-C3N5 as a p-dopant into PM6, improving the charge mobility and hole carrier concentration of PM6. Moreover, the electron transfer between PM6 and g-C3N5 can effectively downshift the Fermi energy level and highest occupied molecular orbital (HOMO) energy level of PM6, which leads to the increase the built-in electric field of organic solar cells (OSCs). The addition of g-C3N5 also effectively enhances the crystallization of active layer, thereby improving the stability of OSCs. As a result, a champion bulk-heterojunction (BHJ) and layer-by-layer (LbL) structure OSCs are successfully achieved featuring a high-power conversion efficiency of 18.10%/18.25%, simultaneously having excellent device stability. This work shows that introducing a low concentration dopant into organic donor is an effective method for improving the electrical performance of organic donor and the efficiency of OSCs.

Achieving High Doping Density in pH-neutral Conjugated Polyelectrolyte Toward Effective Hole-Transporting Materials for Organic Solar Cells.

The lack of effective and non-corrosive hole-transporting layer (HTL) materials has remained a long-standing issue that severely restricts the performance of organic solar cells (OSCs). Most pH-neutral conjugated polyelectrolytes (CPEs) exhibit inferior performance to the acid-doped HTL materials due to their low doping density. In this study, a series of pH-neutral CPEs is designed and synthesized with high doping density as HTL materials. Through an elaborate synthetic route, two sulfonate-terminating alkoxyl side chains can be introduced into thiophene, by which the electron-rich, highly soluble, and chemically stable thiophene monomer is synthesized to enable the subsequent polymerization. The CPE PTT-F exhibit a remarkable self-doping property with an enhanced doping density from 2.01 × 1017 to 7.02 × 1018 cm-3. The high work function and the increased doping density of PTT-F-based HTL decrease the depletion region width from 38.4 to 8.1nm at the anode interface, which minimized the energy loss in hole transport. Consequently, a binary OSC modified by PTT-F-based HTL achieve a high PCE of 18.8%. To the best of the knowledge, this is the highest PCE for OSC employing CPE-based HTL. The results from this work demonstrate an encouraging achievement of realizing exceptional hole collection ability in pH-neutral CPEs.

Influence of sulfurization process in tin sulfide and sulfur mixed vapors on the morphology of Cu2SnS3 thin films

Abstract Cu2SnS3 (CTS) is expected to be an absorber material for next-generation solar cells because it is composed of nontoxic, low-cost elements and has an absorption coefficient of >104 cm−1. In this study, the effects of sulfurization in tin sulfide (Sn x S y ) and S mixed vapors on various properties of CTS were investigated by using a 3-zone tube furnace to suppress carrier recombination at the grain boundaries and control the composition of the CTS. The CTS deposited via sulfurization in S vapor only (1-zone CTS) contained different monoclinic and tetragonal CTS structures. The grain size of the CTS thin films deposited via sulfurization in Sn x S y and S mixed vapors was not increased. On the other hand, crystal structure analysis revealed that the CTS had grown to single-phase monoclinic CTS. The results suggest that precipitation in Sn x S y and S mixed vapors contributes to the growth of monoclinic CTS with suitable power-generation characteristics. This finding is important for realizing high-efficiency CTS-based solar cells.

Synthesis and scalable process for fabrication of Perovskite Solar Cells using organic and inorganic hole transport materials

The Organic Inorganic Lead Iodide perovskite material has emerged as a pioneer in being an active material for third-generation solar cells. Apart from the synthesis, the scalable mechanism which is being used for the deposition process, greatly influences the performance of the cell owing to its impact on the morphology, uniform thickness, and interface between two functional layers. This study briefly discusses the various deposition processes involved in assembling the layers of perovskite solar cells (PSC). Hole transport materials (HTM) are a crucial part of the PSC providing efficient transport of the charge carriers. However, the effect of organic and inorganic HTMs is highly pronounced in the PSCs. This study also discusses the effect of organic and inorganic HTM on the stability and efficiency of the sandwich-structured PSC.

Luminescent Materials for Dye-Sensitized Solar Cells: Advances and Directions

Luminescent Materials for Dye-Sensitized Solar Cells: Advances and Directions

Zinc telluride material properties for solar cell application: Absorber layer

Over recent years, Zinc Telluride (ZnTe) has garnered significant interest from researches. This p-type semiconductors boasts a broad band gap, rendering it valuable in various optoelectronic uses like solar cells, LEDs, and laser displays. Given the growing interest in environmentally friendly energy alternatives, exploring the potential of nano-scale semiconducting materials for solar cells is particularly intriguing. ZnTe stands out due to its direct, wide, and adjustable optical band gap, along with its simple doping process, positioning it as a promising candidate for applications in photochemistry. This study aims to consolidate the research conducted by multiple investigators concerning the optical characteristics and electrical attributes of ZnTe thin films. The primary focus is on understanding how deposition methods and doping impacts these properties. The investigation reveals that the diverse doping techniques employed by different researchers have been extensively examined, demonstrating a positive influence of doping on these properties as well. Following the creation of solar cells based on ZnTe, they have emerged as viable and competitive substitutes for silicon solar cells, thanks to their economical nature and stable performance. As a result, there has been notable focus on advancing ZnTe thin film solar cell technology due to their promising capacity to serve as sustainable energy generators.

Investigation of perovskite materials for solar cells using scanning tunneling microscopy.

The issue of energy scarcity has become more prominent due to the recent scientific and technological advancements. Consequently, there is an urgent need for research on sustainable and renewable resources. Solar energy, in particular, has emerged as a highly promising option because of its pollution-free and environment-friendly characteristics. Among the various solar energy technologies, perovskite solar cells have attracted much attention due to their lower cost and higher photoelectric conversion efficiency (PCE). However, the inherent instability of perovskite materials hinders the commercialization of such devices. The utilization of scanning tunneling microscopy/spectroscopy (STM/STS) can provide valuable insights into the fundamental properties of different perovskite materials at the atomic scale, which is crucial for addressing this challenge. In this review, we present the recent research progress of STM/STS analysis applied to various perovskites for solar cells, including halide perovskites, two-dimensional Ruddlesden-Popper perovskites, and oxide perovskites. This comprehensive overview aims to inspire new ideas and strategies for optimizing solar cells.

Investigation of Energy Deposition by Soft X-rays into Solar Cell Materials

A high-altitude nuclear detonation releases a significant portion of energy as X-rays with a blackbody spectrum. Satellites are particularly vulnerable to prompt soft X-rays (~1 keV) absorbed within a few microns of the surface of the solar array, causing melting and evaporation of its materials. The absorption of soft X-rays in solar cell materials is studied using GEANT4 computer software. Energy deposition as a function of depth (depth-dose profile) is calculated for slab geometries of dielectric and metallic materials. The photo-absorption and Compton scattering of X-rays and the contribution of secondary radiation, such as photo-electrons, Auger-electrons, and fluorescence photons are taken into account. The effect of the production of secondary radiation on the distribution of deposited dose in the near-surface region of materials is investigated. The results presented in this work are validated against published data and provide valuable insights into X-ray absorption by solar cell materials, the redistribution of energy by secondary radiation, and the spatial scale of power density deposition that can be used as a source term for the further thermomechanical analysis of a material’s phase transformations and melting.

The first principle calculations of band offsets among Cs2(Ti, Zr, Hf)X6 double halide perovskites

This study investigates the band offsets among Cs2(Ti, Zr, Hf)X6 double halide perovskites. Valence band offsets (VBO) and conduction band offsets (CBO) were calculated using density functional theory (DFT) with the Perdew–Burke-Ernzerhof (PBE) functional and the hybrid Heyd–Scuseria–Ernzerhof (HSE) functional, employing the supercell technique. This technique offers greater accuracy and reliability by explicitly calculating the potential differences at the interface. A critical factor influencing the results is the contribution of the dipole potential (VD), which induces shifts in the VBO and CBO by approximately 0.2 to 0.6 eV relative to values predicted by the electron affinity rule. This discrepancy arises from the inclusion of interface-specific effects, such as charge redistribution and polarization. Additionally, the findings indicate that the energy band alignments among these compounds are type-I within the same group of halides, with nearly identical lattice constants for Zr- and Hf-based compounds due to their similar ionic radii. These results provide valuable insights for the design of heterostructures in electronic applications and highlight the potential of Cs2(Ti, Zr, Hf)X6 compounds as efficient materials for solar cells, light-emitting diodes, and photodetectors.