Charge Recombination Resistance Research Articles

Designing ferrocenyl thiophene chalcones as light harvester candidates for dye-sensitized solar cells

In dye-sensitized solar cells (DSSCs), the dye (or photosensitizer) plays a crucial role. It absorbs light and generates electrons, which affects the efficiency of converting sunlight into electricity. While Ru(II)-based dyes are common in DSSCs, their scarcity, susceptibility to degradation, and limited absorption range pose challenges for wider adoption. Three new ferrocenyl-thiophene compounds have been synthesized, all sharing the same core structure, but the distinctive difference is the existence of methyl group (CH3) and bromine (Br) substituents attached to the thiophene ring. Using the structures obtained from spectroscopic and X-ray crystallography analyzes, the chemical reactivity of these compounds is theoretically evaluated. Cyclic voltammetry (CV) analysis and electrochemical impedance spectroscopy (EIS) were employed to investigate the redox properties and electron transport mechanisms of the material. The bromination process demonstrates its efficacy for dye applications, while the methyl attachment to the thiophene ring enhances anchoring toward TiO₂, contributing to improved performance in DSSCs. Overall, the compound featuring bromine exhibited a lower band gap compared to the others, resulting in higher efficiency in solar simulation analysis, nearly double that of the methyl-containing compound, and significantly surpassing the plain thiophene compound. EIS analysis revealed that, among the three ferrocenyl chalcone dyes, the bromine-containing compound exhibited the highest charge recombination resistance and longest electron lifetime.

Analysis and design of 25.3% efficient Sb2Se3 solar cells by numerical simulation

Sb2Se3 has a high absorption coefficient of 105 cm−1 in the visible light range, which is an excellent absorber layer material. Currently, a better band alignment between conventional CdS and Sb2Se3 has led to the widespread adoption of CdS as the electron transport layer (ETL) in Sb2Se3 solar cells. However, CdS is toxic, necessitating the exploration of alternative ETL materials that are eco-friendly and possess an appropriate energy band with Sb2Se3. In this study, we endeavor to pioneer an all-inorganic, green solar cell structure of Au/MoS2/Sb2Se3/WS2/ITO by employing MoS2 as the hole transport layer (HTL) and WS2 as the ETL. We primarily optimized Sb2Se3 thickness and its hole doping concentration (NA) by SCAPS-1D numerical simulation. Based on the analysis of built-in electric field and carrier recombination rate along Sb2Se3, the optimal thickness and NA ranges of Sb2Se3 are determined, which are 0.9–1.1 μm and 1016-1018 cm−3 respectively. Through a series of optimization, the structure achieves the highest power conversion efficiency (PCE) of about 25.3 % in the current simulation of Sb2Se3 solar cells. After comparing the novel WS2 ETL with the conventional CdS ETL, we find that WS2 has a larger built-in potential (Vbi) and charge recombination resistance (Rrec). In addition, from the analysis of energy band structure, the spike-like band at Sb2Se3/WS2 interface can effectively inhibit the carrier recombination, which makes the device obtain a larger open circuit voltage (VOC) of 0.69 V. This study can provide theoretical reference for the development of non-toxic and efficient Sb2Se3 solar cells.

Effect of UV‐ozone treatment for KCl interlayer in perovskite solar cells

AbstractThe performance of perovskite solar cells (PSCs) is significantly governed by the interface of perovskite layer. Therefore, a great deal of attention has been paid to the interface engineering of perovskite layer to improve the performance of PSC. In the meantime, KCl is one of the popular molecules being utilized for the interface treatment between SnO2 and perovskite. In this study, we investigate the effect of UV‐ozone (UVO) treatment of KCl interlayer on the photovoltaic performance. A device employing UVO‐treated KCl shows a higher power conversion efficiency mainly based on an increased open‐circuit voltage (VOC). Ultraviolet photoelectron spectroscopy analysis indicates that the UVO treatment induces a rearrangement of energy level at the interface, being responsible for the increase in VOC. Accordingly, an increased charge recombination resistance is evidenced by impedance spectroscopy owing to the inhibited recombination at the SnO2 and perovskite interface by the aid of the aligned energy level.

Solution‐Processed Sb2(S,Se)3 Seed‐Assisted Sb2Se3 Thin Film Growth for High Efficiency Solar Cell

Antimony selenide (Sb2Se3) emerges as a promising sunlight absorber in thin film photovoltaic applications due to its excellent light absorption properties and carrier transport behavior, attributed to the quasi‐one‐dimensional Sb4Se6‐nanoribbon crystal structure. Overcoming the challenge of aligning Sb2Se3‐nanoribbons normal to substrates for efficient photogenerated carrier extraction, a solution‐processed nanocrystalline Sb2(S,Se)3‐seeds are employed on the CdS buffer layer. These seeds facilitate superstrated Sb2Se3 thin film solar cell growth through a close‐space sublimation approach. The Sb2(S,Se)3‐seeds guided the Sb2Se3 absorber growth along a [002]‐preferred crystal orientation, ensuring a smoother interface with the CdS window layer. Remarkably, Sb2(S,Se)3‐seeds improve carrier transport, reduce series resistance, and increase charge recombination resistance, resulting in an enhanced power conversion efficiency of 7.52%. This cost‐effective solution‐processed seeds planting approach holds promise for advancing chalcogenide‐based thin film solar cells in large‐scale manufacturing.

Sol-gel CdS layer for TiO2 nanorod-based quantum dots-sensitized solar cells

The CdS layer was essential for CdSe quantum dot-sensitized solar cells (QDSSCs) as the seed layer and energy barrier. Here, a novel sol–gel method was employed to prepare the CdS interlayer (SG-CdS) for TiO2 nanorod-based QDSSCs. Due to the sufficient reaction of the Cd and S sources in the sol–gel solution, SG-CdS exhibited fewer impurities than CdS produced by commonly used chemical bath deposition (CBD-CdS). QDSSCs with SG-CdS exhibited an open-circuit voltage of 490 mV, a short-circuit current density of 14.12 mA cm−2, and a fill factor of 0.35. The power conversion efficiency of the QDSSCs with SG-CdS was 2.48%, which was higher than that of the QDSSCs with CBD-CdS (2.02%). Moreover, electrochemical impedance spectroscopy showed that the QDSSCs with SG-CdS yielded a charge recombination resistance of 99.92 Ω at a bias voltage of −0.5 V, demonstrating less charge recombination than the QDSSCs with CBD-CdS (82.16 Ω). Therefore, the performance of the CdSe QDSSCs could be improved by reducing the impurities in CdS. This study revealed the advantages of SG-CdS in replacing CBD-CdS as the interlayer for charge transport, as well as good applicability with nanorod photoanodes in QDSSCs.

Rapid Evaporation of a Metal Electrode for a High-Efficiency Perovskite Solar Cell.

Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted considerable attention due to the excellent optoelectronic properties of perovskite materials. The energy consumption and high cost issues of metal electrode evaporation should be addressed before large-scale manufacturing and application. We developed an effective metal electrode evaporation procedure for the fabrication of high-efficiency planar heterojunction (PHJ) PSCs, with an inverted device structure of glass/indium tin oxide (ITO)/poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA)/perovskite/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM)/(E)-β-caryophyllene (BCP)/Ag. The effect of the evaporation rate for an evaporator with a small-volume metal cavity on the performance of PHJ-PSC devices was investigated systematically. Through controlling the processes of Ag electrode evaporation, the charge dynamics of the devices were studied by analyzing their charge recombination resistance and lifetime, as well as their defect state density. Our findings reveal that the evaporation rate of an evaporator with a small cavity is favorable for the performance of PHJ-PSCs. As a result, PHJ-PSCs fabricated using a very thin, non-doped PTAA film exhibit photoelectric conversion efficiency (PCE) of 19.21%, with an open-circuit voltage (Voc) of 1.132 V. This work showcases the great potential of rapidly evaporating metal electrodes to reduce fabrication costs, which can help to improve the competitiveness in the process of industrialization.

Flavonoid from Hedera helix fruits: A promising new natural sensitizer for DSSCs

Owing to their lower cost, simplicity of manufacture, environmental friendliness, and accessibility of raw materials, natural dyes emerge as the most viable substitute for dye-sensitized solar cells (DSSCs). However, the photovoltaic performance of DSSCs based on natural dyes stays behind that of their metal-based counterparts. This can be partially overcome when appropriate chemical additives are present in the redox electrolyte employed in DSSCs based on natural dyes. To determine the ideal additives for DSSCs based on natural dye extracted from Hedera helix fruits, including flavonoid pigments, we thoroughly compare the actions of 1-butyl-3-methylimidazolium iodide, guanidinium thiocyanate, and tert-butylpyridine additives in ionic liquid-based redox electrolytes. These additives suppress undesirable charge recombination and parasitic resistance effects, achieving a more significant enhancement of open-circuit voltage (Voc) of 130 mV and fill factor (FF) of 30 % compared to their counterparts. Utilizing prepared electrolyte solutions in DSSCs also presents an outstanding increase in the efficiency of the devices, from 0.75 % to 1.17 % (∼56 % improvement), which outperforms other natural dye sources containing flavonoid pigments as well. The experimental findings provided in this study demonstrate that the development of electrolytes tailored for natural dyes can lead to greater power conversion efficiency.

A facile strategy for highly efficient perovskite crystals fabricated in a high moisture environment via solvent engineering process

BackgroundHybrid organic perovskite solar cells (PSCs) have recently gained recognition for their excellent photovoltaic properties. However, most PSCs were fabricated in a nitrogen-filled glovebox to prevent damage from moisture. Overcoming humidity damage is crucial for PSC fabrication in an ambient atmosphere. Fabricating perovskite solar cells (PSCs) under ambient atmosphere conditions needs the aid of substrate heating or air-knife flow to rapidly evaporate solvents. MethodsHerein, we propose a facile solvent engineering method without extra equipment or processes for fabricating highly efficient PSCs in a high moisture condition by a one-step spin-coating process. Acetone incorporation into the perovskite precursor solution not only prevents the ingress of moisture, but also accelerates the volatilization of solvents during the crystallization process. Significant findingsThe as-prepared PSCs feature low trap-state density, high charge recombination resistance, low hysteresis, and long charge lifetime. Little MABr and PbBr2 are separated out to passivate interface/grain-boundary defects. At a 10% acetone incorporation, the highest power conversion efficiency can reach 17.75% for the PSC fabricated in 70% relative humidity. The work provides a facile, promising method to prepare highly efficient PSCs in an ambient atmosphere.

Promoting Large-Area Slot-Die-Coated Perovskite Solar Cell Performance and Reproducibility by Acid-Based Sulfono-γ-AApeptide.

Homogeneous and pinhole-free large-area perovskite films are required to realize the commercialization of perovskite modules and panels. Various large-area perovskite coatings were developed; however, at their film coating and drying stages, many defects were formed on the perovskite surface. Consequently, not only the devices lost substantial performance but also their long-term stability deteriorated. Here, we fabricated a compact and uniform large-area MAPbI3-perovskite film by a slot-die coater at room temperature (T) and at high relative humidity (RH) up to 40%. The control slot-die-coated perovskite solar cell (PSC) produced 1.082 V open-circuit voltage (Voc), 24.09 mA cm-2 short current density (Jsc), 71.13% fill factor (FF), and a maximum power conversion efficiency (PCE) of 18.54%. We systematically employed a multi-functional artificial amino acid (F-LYS-S) to modify the perovskite defects. Such amino acids are more inclined to bind and adhere to the perovskite defects. The amino, carbonyl, and carboxy functional groups of F-LYS-S interacted with MAPbI3 through Lewis acid-base interaction and modified iodine vacancies significantly. Fourier transform infrared spectroscopy revealed that the C═O group of F-LYS-S interacted with the uncoordinated Pb2+ ions, and X-ray photoelectron spectroscopy revealed that the lone pair of -NH2 coordinated with the uncoordinated Pb2+ and consequently modified the I- vacancies remarkably. As a result, the F-LYS-S-modified device demonstrated more than three-fold charge recombination resistance, which is one of the primary requirements to fabricate high-performance PSCs. Therefore, the device fabricated employing F-LYS-S demonstrated remarkable PCE of 21.08% with superior photovoltaic parameters of 1.104 V Voc, 24.80 mA cm-2 Jsc, and 77.00%. FF. Concurrently, the long-term stability of the PSCs was improved by the F-LYS-S post-treatment, where the modified device retained ca. 89.6% of its initial efficiency after storing for 720 h in air (T ∼ 27 °C and RH ∼ 50-60%).

Dye‐Sensitized Solar Cells with Efficiency over 36% under Ambient Light Achieved by Cosensitized Tandem Structure

The cosensitization process is an effective way to improve the performance of dye‐sensitized solar cells (DSSCs), especially for tandem cells that employ the complementary light harvest ranges of different dyes. Herein, various cosensitized DSSCs are prepared using D35, XY1b, and Y123 dyes and employed to construct cobalt tandem DSSCs. First, the performance of single cells with and without scattering layers is studied. The results show that the cosensitized cells using D35 + XY1b and XY1b + Y123 dyes have higher power conversion efficiency (PCE) than the others, attributed to their longer light absorption wavelength and higher charge recombination resistance. Furthermore, the XY1b + Y123 cell has significantly higher open circuit voltage (Voc) but slightly lower current density (Jsc) than those of the D35 + XY1b cell. The cosensitized systems are further utilized to prepare tandem cells. Photoelectrodes without and with scattering layers are used as top and bottom cells, respectively. It shows that by using D35 + XY1b (higher Jsc) and XY1b + Y123 (higher Voc) as sensitizers of top and bottom cells, respectively, a PCE as high as 36.27% can be achieved under fluorescent lighting. The cells using these dyes have high long‐term stability at room temperature.

Improvement of the performance of dye-sensitized solar cells employing NickelPalladium alloy-reduced graphene oxide counter electrode: Influence of palladium content

In this work, NickelPalladium-reduced graphene oxide (NiPd-rGO) films have been prepared via liquid phase deposition technique and used as free-platinum (Pt) counter electrode for dye-sensitized solar cell (DSSC). The effect of Pd content in term of various Ni:Pd ratios on the properties such as structure, optical transmission, surface morphology and elemental compositions have been studied. The morphology of NiPd-rGO sample is in the form of crumpled vertical folds in layers and white strips. The influence of Pd content on photovoltaic parameters of the device has also been investigated. The performance parameters were significantly influenced by the Pd content. The device using NiPd-rGO counter electrode prepared at Ni:Pd ratio of 20:2 demonstrated the highest PCE of 3.09%. This is due to the device owns the highest charge recombination resistance (Rrec) and shortest carrier transport time (τ). The efficiency has been improved at the optimum content of Pd. The finding from this work implies that NiPd-rGO is able to substitute Pt as counter electrode in DSSC due to its efficiency is comparable to that of the device employing Pt counter electrode.

Novel pyridoquinazolindone-containing triphenylamine dyes for dye-sensitized solar cells

Four novel “A-D-π-A” pyridoquinazolinone-containing triphenylamine dyes were synthesized for dye-sensitized solar cell (DSSCs), which consist of triphenylamine as the electron donor, thiophene or CC bond as π-bridge, cyanoacrylic acid as the electron acceptor and pyridoquinazolinone as the auxiliary acceptor. Their photophysical, electrochemical properties and photovoltaic performance were investigated. Moreover, density functional theory (DFT) was performed for theoretical calculations. The results show that the incorporation of additional pyridoquinazolinone unit enables dyes with larger charge recombination resistance than the dyes with single pyridoquinazolinone unit, which benefits the increase of Voc. Besides, the introduction of thiophene bridge can broaden and red-shift the absorption region, which endows the dyes with better light-harvesting ability and subsequently brings about superior IPCE and Jsc. Therefore, dye with double pyridoquinazolinone units and thiophene bridge exhibits the best photoelectric conversion efficiency 5.19 % (Jsc = 11.71 mAcm−2, Voc = 0.67 V, ff = 0.70).

Comparative study on the electrochemical synthesis of zinc oxide nanorods using chronoamperometry and chronopotentiometry and their application in inverted polymer solar cells

In this work, the influences of zinc oxide nanorods (ZnO NRs) arrangement, as the electron transport layer (ETL), on the photovoltaic performance of the inverted structure polymer solar cells (PSCs) were studied. Two arrangements of ZnO NRs were electrochemically synthesized on the indium tin oxide (ITO) electrode by chronoamperometry (CA) and chronopotentiometry (CP) techniques at 80 °C. Structural, morphological, optical, and electrochemical features of the prepared samples were compared using different techniques. Applying the CA technique resulted in the vertical growth of ZnO NRs on the ITO electrode. However, flower-like ZnO NRs were formed in the sample prepared by the CP method. The energy levels, charge transfer resistance, recombination resistance, and charge mobility of the prepared samples were evaluated using cyclic voltammetry and electrochemical impedance spectroscopy. Results revealed that the flower-like ZnO NRs prepared by the CP method enjoy a considerably higher (128%) charge mobility of 31.67 × 10−4 cm2/V, lower (17.6%) charge resistance of 32.82 Ω, and higher optical transparency of ∼75.52% at 550 nm. The PSC prepared based on the flower-like ZnO NRs provided a PCE of 4.45, which was about 230.57%, 145.42%, and 302.72% higher than that achieved for the ZnO nanoparticles-, and the vertical ZnO NRs-based devices, and the reference device containing no ETL. Moreover, the flower-like ZnO NRs-based PSC exhibited greater stability in the air and retained about 72% of its initial PCE after 450 h.

Plasmonic Au NPs embedded Ytterbium-doped TiO2 nanocomposites photoanodes for efficient indoor photovoltaic devices

Herein, we present an all-inclusive investigation on the effect of plasmonic gold nanoparticles (Au NPs) embedded Yb-doped TiO2 nanostructured photoanode for efficient photovoltaics devices. Optimally doped Yb (0.5 mol%)-TiO2 nanoparticles (NPs) were synthesised by solid-state grinding. Their structural, morphological, optical, and surface properties were evaluated using XRD, Raman spectroscopy, SEM-EDX, UPS, and XPS. Results show that Yb-doped TiO2 NPs form, reducing the rutile phase and shifting the fermi level. After demonstrating the enhanced properties of Yb-doped TiO2 NPs, we introduced single anatase phase nanowire structures for comparison. Dielectric measurements show Yb-doped TiO2 NW's higher conductivity. Plasmon-induced enhancement of light absorption is achieved by implanting Au NPs into Yb-doped TiO2 NW for additional light harvesting. As a proof of concept, optimised Yb-doped TiO2 photoanode DSSC were fabricated and tested under the AM1.5, 1 sun illumination exhibiting photoconversion efficiency (PCE) of 6 %. Devices employing Yb-doped TiO2 NW: Au NPs photoanode exhibited Jsc to 18.8 % mA-cm−2 and PCE% to 8 %. Under white LED (1000 LUX) exhibited PCE of 13.9 % for Au/Yb-TiO2 NW photoanode. The electrochemical impedance spectroscopy (EIS) measurements on these devices established the Yb-doped TiO2 NW: Au NPs photoanode based device exhibited the lowest charge transport resistance (R2:86 Ω) and charge recombination resistance (R3:20 Ω) which are consistent with the J-V characteristics suggesting the potential use of these photoanode for indoor photovoltaics (IPV) and in general any devices for allied energy and environmental areas of research.

Achieving highly efficient and stable MAPbI3 planar solar cell by embedding Cs+, Fe2+, and Cd2+ metal inorganic cations in perovskite structure

Perovskite solar cells (PSCs) have been attracted the attention of many researchers due to their high conversion efficiency, low manufacturing cost, easy manufacturing steps, high light absorption, and the possibility of changing the photo electronic properties by modifying the chemical structure. Despite the mentioned advantages, the low stability of PSCs and toxicity of lead in the perovskite layer were the challenging issues in this field. In this regard, the use of mixed cation and mixed halide perovskite compounds with high crystal quality, efficiency, and stability has attracted enormous attention. In this project, Fe2+, Cd2+, and Cs+ cations with various contents (Fe2+ + Cd2+: 5% and 10%; Cs+: 5% and 10%) were partially replaced the Pb2+ and CH3NH3+ cations, respectively in the MAPbI3 perovskite structure through a two-step process using spin-coating. The as-synthesized [CsyMA1-yPb1-a-bFeaCdbI3-2aCl2a], (a+b): 5, 10%, y: 5, 10%) perovskites were characterized with X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXRD), and field emission scanning electron microscopy (FESEM). The optical properties of prepared compounds were investigated by ultraviolet–visible (UV–Vis) and photoluminescence (PL) spectroscopy. The photovoltaic behavior as well as stability of solar cells containing MAPbI3, [CsyMA1-yPb1-a-bFeaCdbI3-2aCl2a], (a+b): 5%, y: 5%), and [CsyMA1-yPb1-a-bFeaCdbI3-2aCl2a], (a+b): 10%, y: 10%) perovskites as active layers were evaluated by current density-voltage (I–V) under AM1.5G illumination.Results showed that partial substitution of CH3NH3+ cations with Cs+ and Pb2+ cations with Fe2+ + Cd2+ in the CH3NH3PbI3 structure improved crystallinity and photovoltaic parameters. The average power conversion efficiency (PCE) of six solar cell containing [CsyMA1-yPb1-a-bFeaCdbI3-2aCl2a], (a+b): 10%, y: 10%) perovskite layer was 21.04% which was 1.03 and 1.21 times higher than that cells containing [CsyMA1-yPb1-a-bFeaCdbI3-2aCl2a], (a+b): 5%, y: 5%) and MAPbI3, respectively.The electrochemical impedance spectroscopy (EIS) was utilized to study the charge transfer resistance (Rct) and recombination resistance (Rrec) of prepared solar cells. The Rct and Rrec values of fabricated solar cell were decreased and increased, respectively in the presence of Fe2+, Cd2+, and Cs+ inorganic cations. As a result, the [CsyMA1-yPb1-a-bFeaCdbI3-2aCl2a] perovskites can be considered as the appropriate candidate with high efficiency, stability, and low lead content in the planar perovskite solar cells.

Fabrication of Barium Titanate Nanowires-GNP Composite Bilayer Photoanodes for the High-Performance Dye-Sensitized Solar Cells

Inorganic perovskite barium titanate nanowires (BTNWs) and their nanocomposites comprised of different weight percentages (1, 2, and 3 wt%) of graphene nanoplatelets (GNP) are synthesized via a hydrothermal method and used as photoanode materials of dye-sensitized solar cells (DSSCs). Morphological analysis of the BTNWs and BTNWs + GNP composites has indicated that the one-dimensional BTNWs and two-dimensional GNP are formed as uniformly distributed, well-connected mesoporous microstructures. UV–visible absorption and Raman studies of the BTNWs + GNP composites have revealed a narrowing bandgap, improved visible light absorption with increasing GNP content, and a superior light-scattering effect of BTNWs. Besides, four different DSSC bilayer photoanodes comprising titanium dioxide nanoparticles (TNP) underlayer and an upper layer with BTNWs + (0, 1, 2, and 3 wt%) GNP composites are fabricated to elucidate the TNP + BTNWs and BTNWs + GNP composite sublayer(s) influences on the photovoltaic performance. The TNP + BTNWs + 2 wt% GNP composite bilayer photoanode has demonstrated a higher power conversion efficiency of 9.92 % as compared to that of the other TNP + BTNWs + GNP composite bilayer photoanodes in DSSCs, due to the higher charge recombination resistance, faster charge transport, superior charge collection ability and carrier lifetime of its sublayers.

Manipulating the Migration of Iodine Ions via Reverse-Biasing for Boosting Photovoltaic Performance of Perovskite Solar Cells.

Perovskite solar cells (PSCs) are being developed rapidly and exhibit greatly potential commercialization. Herein, it is found that the device performance can be improved by manipulating the migration of iodine ions via reverse-biasing, for example, at -0.4V for 3min in dark. Characterizations suggestthat reverse bias can increase the charge recombination resistance, improve carrier transport, and enhance built-in electric field. Iodine ions including iodine interstitials in perovskites are confirmed to migrate and accumulate at the SnO2 /perovskite interface under reverse-basing, which fill iodine vacancies at theinterface and interact with SnO2 . First-principles calculations suggest that the SnO2 /perovskite interface with less iodine vacancies has a stronger interaction and higher charge transfer, leading to larger built-in electric field and improved charge transport. Iodine ions that may pass through the SnO2 /perovskite interface are also confirmed to be able to interact with Sn4+ and passivate oxygen vacancies on the surface of SnO2 . Consequently, an efficiency of 23.48% with the open-circuit voltage (Voc ) of 1.16V is achieved for PSCs with reverse-biasing, as compared with the initial efficiency of 22.13% with aVoc of 1.10V. These results are of great significance toreveal the physics mechanism of PSCs under electric field.

Optical and Electrical Transport Properties of the ZnO:CdO Composite Film

In this work, zinc oxide films and composite ZnO:CdO films with cadmium oxide concentrations of 3 , 5 , 7 , 10 , and 12 were obtained by spin-coating on FTO. The films were annealed in the atmosphere under the same temperature conditions of 450°C. The morphology of ZnO:CdO composite films was studied by the SEM method and an electron-dispersion analysis of the concentration of the studied substance was carried out. The influence of the surface morphology of the composite film with an increase in the CdO concentration from 3 to 12 on the optical and electrotransport properties of the ZnO:CdO composite film was studied. The optical absorption spectra of composite films of zinc oxide and cadmium were measured. ATauc plot is presented to determine the band gap of a ZnO:CdO composite film. It has been established that an increase in the CdO concentration on the ZnO surface leads to a decrease in the optical band gap. The observed decrease in the optical band gap of the film with increasing CdO is due to the small band gap of CdO. The method of impedance spectroscopy was used to study the main electrophysical characteristics, in particular, the dynamics of charge carrier transfer in nanocomposite films based on ZnO:CdO. It has been established that the CdO layer on the ZnO surface contributes to a decrease in the resistance value of the composite film Rw, an increase in the charge recombination resistance parameter Rrec at the interface, and an increase in the efficiency of electron injection.

Passivation and energy-level change of the SnO2 electron transport layer by reactive titania for perovskite solar cells

Reactive anatase titania (TAc) are incorporated into SnO2 to form a single TAc-SnO2 electron transport layer (ETL) for mixed-cation perovskite solar cells (PSCs). The TAc-SnO2 layer is prepared in a low-temperature process by the advantage of high crystallinity and surface reactivity of TAc. The influence and mechanism of the TAc incorporation on the photovoltaic performance of PSCs are investigated. The TAc-SnO2 ETL presents rapid electron transfer, low trap density, high charge recombination resistance, low hysteresis and good stability. The 2.5-wt% TAc incorporation reveals the highest power conversion efficiency of 20.12 %, a 19 %-fold enhancement compared to the pristine cell with the SnO2 ETL. The enhancement arises from the fact that the TAc can fill up breaching in the pristine SnO2 layer and adjust the ETL energy level. The carboxyl groups of TAc facilitate the formation of solid bonding among SnO2/TAc colloids and prevent ions from accumulation at the interface of ETL/perovskite. The work provides a facile way to fabricate a low-temperature, single-layer and effective ETL for highly efficient PSCs.

Small Molecules Containing Amphoteric Imidazole Motifs as Sensitizers for Dye-Sensitized Solar Cells: An Overview.

Organic dyes, porphyrins and inorganic complexes containing imidazole (IM) motifs have been demonstrated as a new class of sensitizers in dye-sensitized solar cells (DSSCs). Particularly, the amphoteric nature of IM-based motifs allows them to be used as donors (D), auxiliary donors (DA), linker/branch (π), or acceptors (A) in D-π-A-based organic dyes and porphyrins and also employed as cyclometalated heteroleptic and ancillary ligands in the Ru(II) and Ir(III) complexes for DSSCs. It is noteworthy that the introduction of IM chromophores in the dyes of D-π-A configuration can improve the light-harvesting properties and prohibit the charge recombination reactions due to the extension of the π-conjugated structures and hydrophobic nature. Similarly, in the case of inorganic complexes, the presence of IM motifs as ligands can improve the light-harvesting ability, give facilely tuned HOMO and LUMO energy levels, increase the charge recombination resistance and photostability. This results in enhanced photocurrent (JSC) and photovoltage (VOC) and consequently solar-to-power conversion efficiency (η) of DSSC devices based on Ru(II) and Ir(III) complexes. Considering the interesting DSSC applications of IM-derived molecules, in this review, we therefore comprehensively discuss their photophysical, electrochemical and photovoltaic properties reported so far and establish their structure-activity relationship to further advance the η of DSSCs. To the best of our knowledge, there is no such a review interpreting the importance of molecules possessing IM-motifs for DSSC applications to date.