Study of Pb-based and Pb-free perovskite solar cells using Cu-doped Ni1-xO thin films as hole transport material

SCAPS solar cell simulation program was applied to model an inverted structure of perovskite solar cells using Cu-doped Ni_1-xO thin films as hole transport layer. The Cu-doped Ni_1-xO film were made by co-sputtering deposition under different deposition conditions. By increasing the amount of the Cu-dopant, the film crystallinity enhanced whereas the bandgap energy decreased. The transmittance of the thin films decreased significantly by increasing the sputtering power of copper. High quality, uniform, compact, and pin-hole free films with low surface roughness were achieved. The structural, chemical, surface morphology, optical, electrical, and electronic properties of the Cu doped Ni_1-xO films were used as input parameters in the simulation of Pb-based (MAPbI_3-xCl_x) and Pb-free (MAGeI₃) perovskite solar cells. Simulation results showed that the performance of both Pb-based and Pb-free perovskite solar cell devices significantly enhanced with Cu-doped Ni_1-xO film. The highest power conversion efficiency (PCE) for the Pb-free perovskite solar cell is 8.9% which is lower than the highest PCE of 17.5% for the Pb-based perovskite solar cell.     

The Influence of Physical Properties of ZnO Films on the Efficiency of Planar ZnO/Perovskite/P3HT Solar Cell

ZnO thin films prepared by pulsed laser deposition at low temperature are utilized as the electron transport layer in CH₃NH₃PbI_3?xCl_x‐based perovskite solar cells with a planar heterojunction structure. Oxygen pressure greatly influences the transparent and conductive properties of ZnO films, which are extremely important as electron transport layer for the perovskite solar cells. The transparent and conductive properties of the films under different oxygen pressures are studied by ultraviolet‐visible spectrophotometer and Hall effect measurement system. Through controlling the oxygen pressure, transparent ZnO films with high conductivity are grown and adopted as electron transport layer for planar perovskite solar cell with a power conversion efficiency of 6.3%. After further surface modification of ZnO electron transport layer with [6,6]‐phenyl‐C61‐butyric acid methyl ester, the efficiency of the planar solar cell increases to 7.5%.     

Stable Tin Chloride Perovskite Sensitized Silver Doped Titania Nanosticks Photoanode Solar Cells with Different Hole Transport Materials

Perovskite sensitized solar cells (PSSCs) have recently been catapulted to the cutting edge of thin-film photovoltaic research and development because of their promise for higher power conversion efficiencies and ease of fabrication. In this work, an attempt has been made to fabricate CH₃NH₃SnCl₃ perovskite sensitized silver doped titania nanosticks photoanode solar cells with an efficient hole transport material (HTM), spiro-MeOTAD, poly(3-hexylthiophene-2,5-diyl) (PTTA) and CuI and attained light to electricity power conversion efficiency (PCE) of 10.46, 7.89 and 6.05 % respectively, under AM 1.5G illumination of 100 mW/cm² intensity. As well, PSSCs made with redox couple electrolytes namely quasi-solid state electrolyte (QSSE) and ionic liquid (IL) electrolyte exhibited the PCE of 4.92 and 3.20 % respectively. A metal oxide (HfO₂) layer is coated on the perovskite sensitized photoanode, which could increase the stability of PSSCs. The current density (Jsc)–open circuit voltage (Voc) study shows that PSSCs made with HTMs exhibited better fill factor and PCE. The electron impedance spectroscopy revealed that the electron lifetime (τ_n), electron mobility (µ) and charge collection efficiency (η_cc)in the PSSCs are in the order spiro-MeOTAD > PTTA > CuI > QSSE > IL. This work expresses that the nature of the HTM is essential for charge recombination and elucidates that finding an optimal HTM for the perovskite solar cell includes controlling the perovskite/HTM interaction.     

A KMnF3 perovskite structure with improved stability,low bandgap and high transport properties

Here, a new promising perovskite structure of KMnF₃ has been fabricated and characterized, which yields bandgap of 1.6?eV with fascinating moisture-resistance and phase stability. Investigation of structural, optical, stability and transport properties have done by XRD, SEM, UV–vis–NIR spectroscopy, photoluminescence and electrical conductivity test. Such examination indicated the high carrier mobility (18?cm²/V?s) and density (10¹⁴/cm³) even after a long interval between each excitation. These transport properties are comparable to that of the organic perovskite, indicating the importance of KMnF₃ for solar device applications.     

Optimizing the Aspect Ratio of Nanopatterned Mesoporous TiO2 Thin-Film Layer to Improve Energy Conversion Efficiency of Perovskite Solar Cells

The energy conversion efficiency (ECE) (η), current density (J_sc), open-circuit voltage (V_oc), and fill factor (ff) of perovskite solar cells were studied by using the transmittance of a nanopatterned mesoporous TiO₂ (mp-TiO₂) thin-film layer. To improve the ECE of perovskite solar cells, a mp-TiO₂ thin-film layer was prepared to be used as an electron transport layer (ETL) via the nanoimprinting method for nanopatterning, which was controlled by the aspect ratio. The nanopatterned mp-TiO₂ thin-film layer had a uniform and well-designed structure, and the diameter of nanopatterning was 280 nm. The aspect ratio was controlled at the depths of 75, 97, 127, and 167 nm, and the perovskite solar cell was fabricated with different depths. The ECE of the perovskite solar cells with the nanopatterned mp-TiO₂ thin-film layer was 14.50%, 15.30%, 15.83%, or 14.24%, which is higher than that of a non-nanopatterned mp-TiO₂ thin-film layer (14.07%). The enhancement of ECE was attributed to the transmittance of the nanopatterned mp-TiO₂ thin-film layer that is due to the improvement of the electron generation. As a result, better electron generation affected the electron density, and J_sc increased the V_oc, and ff of perovskite solar cells.     

CBD方法制备的Zn(O,S)薄膜的微结构表征及性能

对低温化学浴沉积方法制备的Zn（O,S）薄膜进行了研究,通过XPS、SEM、XRD、拉曼光谱、PL谱、紫外-可见吸收光谱等手段对薄膜的形貌、结构及组成进行系统表征,探究了其作为钙钛矿电池电子传输层的可能性。研究表明：化学浴沉积（CBD）方法制备的Zn（O,S）薄膜为ZnO、ZnS和ZnOS合金的复合膜;该薄膜对CH₃NH₃PbI₃光吸收层具有与TiO₂相当的电子抽提能力,是一种可供选择的高效柔性钙钛矿电池电子传输层材料。     

Superior optoelectrical properties of magnetron sputter-deposited cerium-doped indium oxide thin films for solar cell applications

Indium tin oxide (ITO) is the most commonly used front contact material for a variety of photovoltaic technologies. However, the presence of a high free carrier concentration in ITO thin films results in the well-known phenomenon of free carrier absorption in the near-infrared (NIR) region of the solar spectrum. This causes optical losses especially in those solar cells where the active layer is designed to preferentially absorb NIR photons. Therefore, a combination of high carrier mobility and high NIR transparency is desired for advanced transparent conductive oxides for substituting ITO in solar cells. In this work, cerium-doped indium oxide (ICeO) thin films are deposited by pulsed DC magnetron sputtering, giving a remarkable 137% improvement of the mobility (71 cm² V^?1 s^?1) compared to the previous record value of 30 cm² V^?1 s^?1 for DC magnetron sputtered cerium-doped ITO films on glass. When compared to conventional ITO films prepared in this work, the highest mobility of ICeO is found to be almost four times higher and also the NIR transmission is substantially enhanced. Theoretical modelling of the experimental results indicates that neutral impurity scattering limits the carrier mobility in our films. With the recent advancements in single and multi-junction organic and perovskite solar cells, the development of ICeO/glass substrates (as possible replacements for the commonly used ITO/glass substrates) demonstrates significant potential in minimizing optical losses in the NIR region.     

Lead free CsSn0.5Ge0.5I3 perovskite solar cell with different layer properties via SCAPS-1D simulation

Organic–inorganic halide perovskite solar cells (PSCs) have been extensively studied due to their simple fabrication methods and obvious device efficiency advantages. In this work, the perovskite CsSn_0.5Ge_0.5I₃ is used as the light absorption layer, which is doped with Ge²⁺ in CsSnI₃ to improve its stability. The polymers of 3-hexylthiophene (P3HT) with excellent optoelectronic properties and low price, and SnO₂ with high electron extraction ability is selected as charge transport layers. Based on these, a novel PSC structure (FTO/SnO₂/IDL1/CsSn_0.5Ge_0.5I₃/IDL2/P3HT/Au) has been simulated via solar cell capacitor simulator (SCAPS-1D). The PSC performance is optimized by adjusting a series of parameters, including the layer thickness, defect density, electron affinity potential energy, and operating temperature, and so forth. The results show that the PSC defects are passivated by adjusting the appropriate parameters, and the final optimized open circuit voltage (V_OC) is 1.08 V, short-circuit current density (J_SC) is 27.37 mA/cm², fill factor (FF) is 83.32%, while the power conversion efficiency (PCE) is increased from the initial 10.89% to 24.63%, which provides theoretical reference for experiments and new ideas for the preparation and development of efficient and environmentally friendly PSCs. Finally, the effect of different metal cathodes with and without hole transport layer (HTL) on PSC performance is compared. The PSCs without HTL are more dependent on battery cathodes, which provided a way to replace precious metals with other electrode materials.     

Structural,optical, and electrical properties of tin iodide-based vacancy-ordered-double perovskites synthesized via mechanochemical reaction

Over the recent past, lead-based halide perovskite materials have drawn significant attention due to their excellent optical and electrical properties for solar cells and optoelectronics applications. However, the toxicity of lead elements and instability under ambient conditions leads to develop alternative compositions. Herein, we report a novel mechanochemical synthesis of tin iodide-based double perovskites (A₂SnI₆; A = Rb⁺, Cs⁺, methylammonium, and formamidinium), and their structural, optical, and electrical properties are investigated. Importantly, we found that the hydrogen iodide (HI) addition during the ball-milling process minimizes secondary phase formation in the synthesized A₂SnI₆ powders. The effects of HI addition and the A-site substitution are investigated with respect to the lattice parameters, optical bandgaps, and electrical properties of the synthesized perovskite materials. Our results demonstrate essential information to improve the understanding of halide perovskite materials and develop efficient lead-free perovskite photoelectric devices.     

Thermal oxidation of oxynitride films as a strategy to achieve (Sr2Ta2O7)100-x(La2Ti2O7)x based oxide perovskite films with x = 1.65

• •This study concerns STLTO compounds of the ferroelectric (Sr₂Ta₂O₇)_100-x(La₂Ti₂O₇)_x solid solution. The purpose is to produce the STLTO composition x = 1.65 as thin films by thermal oxidation of the corresponding oxynitride composition. Indeed, the combination of an STLTO oxide target with a dioxygen-rich reactive atmosphere during the sputtering deposition leads to Sr-deficient oxide thin films, shifting composition and structure from the perovskite to the tetragonal tungsten bronze type. An alternative synthesis pathway is to first deposit, under nitrogen-rich atmosphere, stoichiometric oxynitride films and produce, by thermal annealing under air, the stoichiometric oxide. For low oxidation temperatures ([550–600 °C]), samples remain intact and display an oxide character but still contain a significant amount of nitrogen, they could be described as intermediate phases containing nitrogen-nitrogen pairs as demonstrated by Raman. Dielectric characteristics of these original film materials are of interest with a tunability value of 26 % at 30 kV/cm (10 kHz).

     

Electronic structure and transport properties of sol-gel-derived high-entropy Ba(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3 thin films

High-entropy perovskite thin films, as the prototypical representative of the high-entropy oxides with novel electrical and magnetic features, have recently attracted great attention. Here, we reported the electronic structure and charge transport properties of sol-gel-derived high-entropy Ba(Zr_0.2Sn_0.2Ti_0.2Hf_0.2Nb_0.2)O₃ thin films annealed at various temperatures. By means of X-ray photoelectron spectroscopy and absorption spectrum, it is found that the conduction-band-minimum shifts downward and the valence-band-maximum shifts upward with the increase of annealing temperature, leading to the narrowed band gap. Electrical resistance measurements confirmed a semiconductor-like behavior for all the thin films. Two charge transport mechanisms, i.e., the thermally-activated transport mechanism at high temperatures and the activation-less transport mechanism at low temperatures, are identified by a self-consistent analysis method. These findings provide a critical insight into the electronic band structure and charge transport behavior of Ba(Zr_0.2Sn_0.2Ti_0.2Hf_0.2Nb_0.2)O₃, validating it as a compelling high-entropy oxide material for future electronic/energy-related technologies.     

Influence of gas carrier on morphological and optical properties of nanostructured In2O3 grown by solid-vapour process

Nanostructured indium oxide (In₂O₃) thin film was prepared by solid-vapour deposition method under NH₃ and Ar atmosphere. The influence of gas nature on the growth of In₂O₃ thin film was investigated in terms of structure, morphology and optical properties. X-ray diffraction, Raman spectroscopy and photoluminescence analyses indicated the formation of pure In₂O₃ phase with strong preferred orientation along c-axis, from cubic- to needles-like morphologies. The as-fabricated nanostructured In₂O₃ thin films with tailored morphology, enhanced crystallinity and optical quality can be used for gas sensing, solar cells and other potential applications. In addition, the potential use of NH₃ as carrier gas for an efficient control of morphology/size and optical properties can be proposed for the fabrication of other nanostructured oxides.     

Direct evidence of high oxygen ion conduction of perovskite-type ceramic membrane under hydrogen atmosphere in solid oxide fuel cell

The ionic conduction of perovskite-type oxides remains a fundamental and important issue in the research of solid oxide fuel cells (SOFCs). In this research, a thin perovskite-type ceramic membrane was fabricated in situ at anode side attached to the surface of Gd_0.2Ce_0·8O_1.9 (GDC20) electrolyte membrane. The single cell working between H₂ and static air showed good stability (over 50 h), high open circuit voltages (above 1.0 V) as well as high peak power densities (749-264 mW cm^?2) from 600 to 500 °C. Detailed analyses of current research demonstrated that the thin perovskite film mainly possessed the oxygen ion conductivity under reducing atmosphere, while the proton conductivity was severely suppressed, showing the high flexibility in ionic conductivity of perovskite oxide. This work also implies that the oxygen ion and proton conduction may be in high correlation with each other, which provides important information to unveil the nature of the ionic conduction of perovskite-type oxides.     

Efficient perovskite solar cells based on low-temperature solution-processed (CH3NH3)PbI3 perovskite/CuInS2 planar heterojunctions

In this work, the solution-processed CH₃NH₃PbI₃ perovskite/copper indium disulfide (CuInS₂) planar heterojunction solar cells with Al₂O₃ as a scaffold were fabricated at a temperature as low as 250°C for the first time, in which the indium tin oxide (ITO)-coated glass instead of the fluorine-doped tin oxide (FTO)-coated glass was used as the light-incidence electrode and the solution-processed CuInS₂ layer was prepared to replace the commonly used TiO₂ layer in previously reported perovskite-based solar cells. The influence of the thickness of the as-prepared CuInS₂ film on the performance of the ITO/CuInS₂(n)/Al₂O₃/(CH₃NH₃)PbI₃/Ag cells was investigated. The ITO/CuInS₂(2)/Al₂O₃/(CH₃NH₃)PbI₃/Ag cell showed the best performance and achieved power conversion efficiency up to 5.30%.     

Greatly enhanced photocurrent in inorganic perovskite [KNbO3]0.9[BaNi0.5Nb0.5O3‐σ]0.1 ferroelectric thin‐film solar cell

Inorganic perovskite [KNbO₃]_0.9[BaNi_0.5Nb_0.5O_3‐σ]_0.1 (KBNNO) ferroelectric thin films with narrow band gap (1.83 eV) and high room‐temperature remnant polarization (Pr = 0.54 μC/cm²) was grown successfully on the Pt(111)/Ti/SiO₂/Si(100) substrates by pulsed laser deposition. Ferroelectric solar cells with a basic structure of ITO/KBNNO/Pt were further prepared based on these thin films, which exhibited obvious external‐poling dependent photovoltaic effects. When the devices were negatively poled, the short‐circuit current and open‐circuit voltage were both significantly higher than those of the devices poled positively. This is attributed to enhanced charge separation under the depolarization field induced by the negative poling, which is superimposed with the built‐in field induced by the Schottky barriers at the interfaces between KBNNO and the two electrodes. When a poling voltage of ‐1 V was applied, the device showed a short‐circuit current as high as 27.3 μA/cm², which was by two orders of magnitude larger than that of the KBNNO thick‐film (20 μm) devices reported previously. This work may inspire further exploration for lead‐free inorganic perovskite ferroelectric photovoltaic devices.     

Au Nanoparticles as Interfacial Layer for CdS Quantum Dot-sensitized Solar Cells

Quantum dot-sensitized solar cells based on fluorine-doped tin oxide (FTO)/Au/TiO₂/CdS photoanode and polysulfide electrolyte are fabricated. Au nanoparticles (NPs) as interfacial layer between FTO and TiO₂ layer are dip-coated on FTO surface. The structure, morphology and impedance of the photoanodes and the photovoltaic performance of the cells are investigated. A power conversion efficiency of 1.62% has been obtained for FTO/Au/TiO₂/CdS cell, which is about 88% higher than that for FTO/TiO₂/CdS cell (0.86%). The easier transport of excited electron and the suppression of charge recombination in the photoanode due to the introduction of Au NP layer should be responsible for the performance enhancement of the cell.     

Influence of seed layer on crystal orientation and electrical properties of (Na0.85K0.15)0.5Bi0.5TiO3 thin films prepared by a sol–gel process

Sol–gel derived lead-free (Na_0.85K_0.15)_0.5Bi_0.5TiO₃ (NKBT) thin films, with and without a Pb_0.8La_0.1Ca_0.1Ti_0.975O₃ (PLCT) seed layer, were fabricated on (111)Pt/Ti/SiO₂/Si substrates. The influences of the seed layer on crystal orientation and electrical properties were investigated in detail. XRD indicated that the NKBT thin films fabricated with a seed layer were fully crystallized into a single perovskite structure, while the films fabricated under the same conditions, but without a seed layer, possessed a certain amount of pyrochlore phase. The NKBT film with a 14 nm-thick seed layer showed high (100) orientation, and exhibited enhanced electrical properties, such as a higher remanent polarization (Pr～18 µC/cm²), a lower dielectric loss tangent (tan δ ～0.023) and smaller transient current density (J<10^?5 A/cm²).     

Optimization of the dye-sensitized solar cell performance by mechanical compression

In this study, the P25 titanium dioxide (TiO₂) nanoparticle (NP) thin film was coated on the fluorine-doped tin oxide (FTO) glass substrate by a doctor blade method. The film then compressed mechanically to be the photoanode of dye-sensitized solar cells (DSSCs). Various compression pressures on TiO₂ NP film were tested to optimize the performance of DSSCs. The mechanical compression reduces TiO₂ inter-particle distance improving the electron transport efficiency. The UV–vis spectrophotometer and electrochemical impedance spectroscopy (EIS) were employed to quantify the light-harvesting efficiency and the charge transport impedance at various interfaces in DSSC, respectively. The incident photon-to-current conversion efficiency was also monitored. The results show that when the DSSC fabricated by the TiO₂ NP thin film compressed at pressure of 279 kg/cm², the minimum resistance of 9.38 Ω at dye/TiO₂ NP/electrolyte interfaces, the maximum short-circuit photocurrent density of 15.11 mA/cm², and the photoelectric conversion efficiency of 5.94% were observed. Compared to the DSSC fabricated by the non-compression of TiO₂ NP thin film, the overall conversion efficiency is improved over 19.5%. The study proves that under suitable compression pressure the performance of DSSC can be optimized.     

Surface modification of electron transport layers based on TiO2 nanorod boosts efficiency of perovskite solar cells

In this work, TiO₂ heterostructure thin films including rutile TiO₂ nanorods (TNRs) and anatase TiO₂ nanoparticles (TNPs) on fluorine-doped tin oxide (FTO) glass are fabricated by the hydrothermal method and are applied as electron transport layers (ETLs) in MAPbI₃-based perovskite solar cells (PSCs). To enhance the surface area of ETL, TNRs are first etched in acidic solution by another hydrothermal process for different reaction times before coating with TNPs. The morphological and structural properties of TNRs after etching are carefully investigated. Interestingly, the surface modification of TNR thin film by appropriate TNP deposition and etching improves significantly the efficiency of PSC devices by more than 1.6 times. To further improve the performance of PSC, phenyl-C61-butyric acid methyl ester (PCBM) is used to enhance the charge transfer efficiency at the ETL/perovskite interface, and the optimal PSC device shows the champion efficiency of 18.50% with low charge transfer resistance (11.56 ohms).     

The microstructure,ferroelectric and dielectric behaviors of Na0.5Bi0.5(Ti,Fe)O3 thin films synthesized by chemical solution deposition: Effect of precursor solution concentration

Fe-doped Na_0.5Bi_0.5TiO₃ (NBTFe) thin films were prepared directly on indium tin oxide/glass substrates using a chemical solution deposition method combined with sequential layer annealing. The X-ray diffraction, scanning electron microscopy and insulating/ferroelectric/dielectric measurements were utilized to characterize the NBTFe thin films. All the NBTFe thin films prepared by four precursor solutions with various concentrations of 0.05, 0.10, 0.20 and 0.30 M exhibit polycrystalline perovskite structures with different relative intensities of (l00) peaks. A large remanent polarization (P_r) of 33.90 μC/cm² can be obtained in NBTFe film derived with 0.10 M spin-on solution due to its lower leakage current and larger grain size compared to those of other samples. Also, it shows a relatively symmetric coercive field and large dielectric tunability of 36.34%. Meanwhile, the NBTFe thin film with 0.20 M has a high energy-storage density of 30.15 J/cm³ and efficiency of 61.05%. These results indicate that the electrical performance can be controlled by optimizing the solution molarity.