Preparation and characterization of regioregular poly(3-octylthiophene-2,5-diyl)/copper indium disenillide/titania heterojunction polymer solar cells

By optimizing the P3OT/CISe ratio, TiO₂ content in the P3OT/CISe active layer, annealing temperature and time, this study investigated hybrid Al/Ca/P3OT:CISe:TiO₂/PEDOT:PSS/ITO thin film solar cells with improved efficiency. Due to an increase in charge-carrier transport and a decrease of electron-hole recombination, it is possible to increase the efficiency of hybrid solar cells by adding TiO₂ nanoparticles to the P3OT:CISe active film. Also, performance enhancement of the solar cells can occur with an increase of CISe content in P3OT as well as the addition of a PEDOT:PSS layer to the cell structure. The optimum TiO₂ content in P3OT:CISe layer is 15 wt.%. The optimum annealing temperature and time are 125 °C and 30 min, respectively. The formation of large CISe and TiO₂ aggregates that reduce charge mobility may cause the decrease of efficiency. The rough surface may effectively reduce the charge-transport distance and provide nanoscale phase separation that further enhances internal light scattering and light absorption. The best results for the open circuit voltages (V_oc), short-circuit current density (J_sc), fill factor (FF), and efficiency (η_e) of Al/Ca/POCT15/PEDOT:PSS/ITO hybrid solar cells obtained at optimized conditions were V_oc = 0.49, J_sc = 3.20, FF = 42.96, and η_e = 0.674, respectively.     

The effects of the thickness of TiO2 films on the performance of dye-sensitized solar cells

Nanocrystalline anatase TiO₂ thin films with different thicknesses (0.5-2.0 μm) have been deposited on ITO-coated glass substrates by a sol-gel method and rapid thermal annealing for application as the work electrode for dye-sensitized solar cells (DSSC). From the results, the increases in thickness of TiO₂ films can increase adsorption of the N3 dye through TiO₂ layers to improve the short-circuit photocurrent (J_sc) and open-circuit voltage (V_oc), respectively. However, the J_sc and V_oc of DSSC with a TiO₂ film thickness of 2.0 μm (8.5 mA/cm² and 0.61 V) are smaller than those of DSSC with a TiO₂ film thickness of 1.5 μm (9.2 mA/cm² and 0.62 V). It could be due to the fact that the increased thickness of TiO₂ thin films also resulted in a decrease in the transmittance of TiO₂ thin films thus reducing the incident light intensity on the N3 dye. An optimum power conversion efficiency (η) of 2.9% was obtained in a DSSC with the TiO₂ film thickness of 1.5 μm.     

Sulfurization of electrodeposited CuInSe2-based solar cells

CuInSe₂ (CISe) thin films have been prepared by single-step electrodeposition on top of TCO/TiO₂ and TCO/TiO₂/In₂S₃ coated electrodes. TiO₂ and In₂S₃ have been deposited by spray–pyrolysis. The electrodeposition step is studied using cyclic voltammetry in an acidic electrolyte. Electrodeposited CISe is then subjected to two different thermal treatments. The first treatment is an annealing step under argon atmosphere, carried out to enhance the crystallinity of the film. The second consists of a sulfurization process, where sulfur is vaporized and mixed with the argon flux, leading to substantial changes in the composition of the chalcogenide. The crystallinity, morphology and stoichiometry of the annealed films are characterized by XRD, micro-Raman spectroscopy and SEM/EDX. Raman spectra and EDX show an almost complete replacement of the Se atoms by S atoms. Etching the films in KCN solution is a key step, enabling a final adjustment in the stoichiometry. The incorporation of In₂S₃ buffer layer in TiO₂/CuIn(SeS)₂ solar cells produces a marked improvement in the cell efficiency. Despite this improvement, the values of J_sc and the fill factor (FF) are relatively low, showing efficiencies below 1%, most likely associated to the resistances present in the multi-layered cell.     

High-Efficiency Perovskite Quantum Dot Hybrid Nonfullerene Organic Solar Cells with Near-Zero Driving Force

To take advantages of the intense absorption and fluorescence, high charge mobility, and high dielectric constant of CsPbI₃ perovskite quantum dots (PQDs), PQD hybrid nonfullerene organic solar cells (OSCs) are fabricated. Addition of PQDs leads to simultaneous enhancement of open-circuit voltage (V_OC), short-circuit current density (J_SC), and fill factor (FF); power conversion efficiencies are boosted from 11.6% to 13.2% for PTB7-Th:FOIC blend and from 15.4% to 16.6% for PM6:Y6 blend. Incorporation of PQDs dramatically increases the energy of the charge transfer state, resulting in near-zero driving force and improved V_OC. Interestingly, at near-zero driving force, the PQD hybrid OSCs show more efficient charge generation than the control device without PQDs, contributing to enhanced J_SC, due to the formation of cascade band structure and increased molecular ordering. The strong fluorescence of the PQDs enhances the external quantum efficiency of the electroluminescence of the active layer, which can reduce nonradiative recombination voltage loss. The high dielectric constant of the PQDs screens the Coulombic interactions and reduces charge recombination, which is beneficial for increased FF. This work may open up wide applicability of perovskite quantum dots and an avenue toward high-performance nonfullerene solar cells.     

Highly Efficient Porphyrin‐Based OPV/Perovskite Hybrid Solar Cells with Extended Photoresponse and High Fill Factor

Employing a layer of bulk‐heterojunction (BHJ) organic semiconductors on top of perovskite to further extend its photoresponse is considered as a simple and promising way to enhance the efficiency of perovskite‐based solar cells, instead of using tandem devices or near infrared (NIR)‐absorbing Sn‐containing perovskites. However, the progress made from this approach is quite limited because very few such hybrid solar cells can simultaneously show high short‐circuit current (J_SC) and fill factor (FF). To find an appropriate NIR‐absorbing BHJ is essential for highly efficient, organic, photovoltaics (OPV)/perovskite hybrid solar cells. The materials involved in the BHJ layer not only need to have broad photoresponse to increase J_SC, but also possess suitable energy levels and high mobility to afford high V_OC and FF. In this work, a new porphyrin is synthesized and blended with [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) to function as an efficient BHJ for OPV/perovskite hybrid solar cells. The extended photoresponse, well‐matched energy levels, and high hole mobility from optimized BHJ morphology afford a very high power conversion efficiency (PCE) (19.02%) with high V_oc, J_SC, and FF achieved simultaneously. This is the highest value reported so far for such hybrid devices, which demonstrates the feasibility of further improving the efficiency of perovskite devices.     

Toward High Efficient Cu2ZnSn(Sx,Se1−x)4 Solar Cells: Break the Limitations of VOC and FF

Increasing the fill factor (FF) and the open-circuit voltage (V_OC) simultaneously together with non-decreased short-circuit current density (J_SC) are a challenge for highly efficient Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cells. Aimed at such target in CZTSSe solar cells, a synergistic strategy to tailor the recombination in the bulk and at the heterojunction interface has been developed, consisting of atomic-layer deposited aluminum oxide (ALD-Al₂O₃) and (NH₄)₂S treatment. With this strategy, deep-level Cu_Zn defects are converted into shallower V_Cu defects and improved crystallinity, while the surface of the absorber is optimized by removing Zn- and Sn-related impurities and incorporating S. Consequently, the defects responsible for recombination in the bulk and at the heterojunction interface are effectively passivated, thereby prolonging the minority carrier lifetime and increasing the depletion region width, which promote carrier collection and reduce charge loss. As a consequence, the V_OC deficit decreases from 0.607 to 0.547 V, and the average FF increases from 64.2% to 69.7%, especially, J_SC does not decrease. Thus, the CZTSSe solar cell with the remarkable efficiency of 13.0% is fabricated. This study highlights the increased FF together with V_OC simultaneously to promote the efficiency of CZTSSe solar cells, which could also be applied to other photoelectronic devices.     

Effect of photoelectrode morphology of single-crystalline anatase nanorods on the performance of dye-sensitized solar cells

TiO₂ terpineol-based pastes with nanorods (NRs) of over 25 μm thickness have been prepared for the photoactive electrodes of the dye-sensitized solar cells (DSSCs). The NRs, with a length of approximately 80 nm and an aspect ratio of about 3, are made by a two-step hydrothermal process. They have the single crystalline anatase structure and can be dispersed well in water and ethanol. With a high thermal stability and larger surface area (47.2 m² g^− 1) than commercial TiO₂ particles (P25, 39.1 m² g^− 1), the well-dispersed anatase NR films with aggregate-free morphology are transparent. For the photocurrent-voltage measurements, the NR cell exhibits high short-circuit photocurrent (J_SC) under 1 Sun AM 1.5 simulated sunlight due to the higher surface area and transmittance. The open-circuit voltage (V_OC) of NR films is not obviously reduced with incremental thickness, which results from the one-dimensional single crystalline structure of NR due to less surface defects. As compared with the P25 cell, DSSCs made with NRs have a higher fill factor (FF) because of the uniform void spaces. An enhancement of conversion efficiency from 4.88% for P25 to 5.67% for NR is achieved. The P25 particles are incorporated in NR films as light-scattering centers, while the R1P1 containing 50 wt.% of P25 has a high V_OC and FF as compared with P25, but the J_SC is still lower than that of the NR.     

Rapid thermal melted TiO2 nano-particles into ZnO nano-rod and its application for dye sensitized solar cells

TiO₂ nano-particles with an anchored ZnO nano-rod structure were synthesized using the hydrothermal method to grow ZnO nano-rods and coated TiO₂ nano-particles on ZnO nano-rods using the rapid thermal annealing method on ITO conducting glass pre-coated with nano porous TiO₂ film. The XRD study showed that there was little difference in crystal composition for various types of TiO₂ nano-particles anchored to ZnO nano-rods. The as-prepared architecture was characterized using field-emission scanning electron microscopy (FE-SEM). Films with TiO₂ nano-particles anchored to ZnO nano-rods were used as electrode materials to fabricate dye sensitized solar cells (DSSCs). The best solar energy conversion efficiency of 2.397% was obtained by modified electrode material, under AM 1.5 illumination, achieved up to J_sc = 15.382 mA/cm², V_oc = 0.479 V and fill factor = 32.8%.     

In situ fabrication of Bi2S3 nanocrystal film for photovoltaic devices

A facile wet-chemical method to prepare Bi₂S₃ thin films with flake nanostructures directly on ITO glass substrate is presented in this paper for the first time. The product was characterized by X-ray powder diffractometer (XRD), Raman spectrometer, scanning electron microscope (SEM), and atomic force microscope (AFM). The one-step solvothermal elements treatment on the ITO substrate spare time to form film by spin-coating process and the film could be tightly attached to the ITO electrode. A conjugated polymer, poly 3-hexylthiophene (P3HT), was then spin-coated on the as-prepared Bi₂S₃ film to form an inorganic-organic hybrid thin film. The photovoltaic performance of the resulting solar cell device was also investigated.     

Dye Adsorption Characteristics of Anatase TiO2 Film Prepared in an Aqueous Solution

Anatase TiO₂ film was deposited on SnO₂: F substrate in aqueous solution. The film had an assembly of acicular TiO₂ nanocrystals on the surface. The crystals grew along the c-axis, i.e. perpendicular to the substrate. Dye adsorption increased with film thickness. Intensity of photoluminescence originating from the dye adsorbed on the nanostructured film after annealing was 3 times higher than that of thicker particulate film constructed of TiO₂ nanoparticles (P25). Additionally, dye adsorption property of the film without annealing was two times higher than the film with annealing. Consequently, the as-deposited film had high dye adsorption property which is about 6 times higher that that of thicker particulate film constructed of TiO₂ nanoparticles (P25). Assemblies of acicular crystals on the surface increased the surface area and amount of dye adsorption. The film may be useful for biomolecule sensors and dye-sensitized solar cells.     

Optical and electrical properties of electron-irradiated Cu(In,Ga)Se2 solar cells

The optical and electrical properties of electron-irradiated Cu(In,Ga)Se₂ (CIGS) solar cells and the thin films that composed the CIGS solar cell structure were investigated. The transmittance of indium tin oxide (ITO), ZnO:Al, ZnO:Ga, undoped ZnO, and CdS thin films did not change for a fluence of up to 1.5 × 10¹⁸ cm^− 2. However, the resistivity of ZnO:Al and ZnO:Ga, which are generally used as window layers for CIGS solar cells, increased with increasing irradiation fluence. For CIGS thin films, the photoluminescence peak intensity due to Cu-related point defects, which do not significantly affect solar cell performance, increased with increasing electron irradiation. In CIGS solar cells, decreasing J_SC and increasing R_s reflected the influence of irradiated ZnO:Al, and decreasing V_OC and increasing R_sh mainly tended to reflect the pn-interface properties. These results may indicate that the surface ZnO:Al thin film and several heterojunctions tend to degrade easily by electron irradiation as compared with the bulk of semiconductor-composed solar cells.     

等离子体电解氧化法制备多孔TiO2/V2O5复合物膜层及其增强光催化产氢活性

较差的光催化产氢效率极大地阻碍了TiO₂光催化剂的工业化应用。为此,本文在含有NH₄VO₃的磷酸盐溶液中,采用等离子体电解氧化(PEO)法制备了多孔TiO₂/V₂O₅复合膜光催化剂,通过扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射(XRD)、X射线光电子谱(XPS)和紫外可见漫反射光谱(UV-Vis DRS)对其组成、结构及光吸收性质进行了表征,并采用气相色谱评价了薄膜催化剂的光催化产氢性能,研究了电解液中NH₄VO₃含量对膜的结构、组成和光催化产氢性能的影响。结果表明:复合膜催化剂主要由锐钛矿和金红石型TiO₂组成,具有微孔结构,V₂O₅主要以无定形形式存在于膜中,与TiO₂有很强的相互作用,影响TiO₂的晶面间距。研究发现,元素V抑制了TiO₂的结晶和金红石型TiO₂的形成,扩大了薄膜的光学吸收范围。针对Na₂S+ Na₂SO₃溶液中的光催化产氢性能的研究显示,在质量浓度为1 g/L NH₄VO₃的电解液中制备的TiO₂/V₂O₅薄膜的光催化活性最高,优于近年来报道的其他光催化剂。光催化重复实验表明,该复合膜催化剂具有较高的稳定性和较为恒定的光催化活性。     

HFCVD grown graphene like carbon–nickel nanocomposite thin film as effective counter electrode for dye sensitized solar cells

The two step processes of hot filament chemical vapor deposition (HFCVD) and DC sputtering were used to grow graphene like carbon (GLC)–nickel (Ni) nanocomposite thin film on fluorine-doped tin oxide (FTO) glass and applied as counter electrode (CE) for dye sensitized solar cells (DSSCs). The morphological and absorption properties revealed uniform GLC–Ni thin film with reasonable transmittance. The GLC–Ni thin film showed enhanced electrical conductivity as compared to FTO. The good electrocatalytic activity towards iodide ions in redox electrolyte was showed by the prepared GLC–Ni/FTO thin film electrode. The fabricated DSSC with GLC–Ni/FTO counter electrode (CE) presented relatively moderate solar-to-electrical conversion efficiency of ∼3.1% with high short-circuit current density (J_SC) of ∼10.03 mA/cm², open circuit voltage (V_OC) of ∼0.663 V with fill factor (FF) of ∼0.45, which might attribute to enhanced electrical conductivity and the electrocatalytic activity of GLC–Ni/FTO CE.     

All-chemically deposited Bi2S3/PbS solar cells

We report on solar cells with a cross-sectional layout: TCO/window/Bi₂S₃/PbS, in which a commercial SnO₂ transparent conductive oxide (TCO-PPG Sungate 500); chemically deposited window layers of CdS, ZnS or their oxides; n-type Bi₂S₃ (100 nm) and p-type PbS (360-550 nm) absorber films constitute the cell structures. The crystalline structure, optical, and electrical properties of the constituent films are presented. The open circuit voltage (V_oc) and short-circuit current density (J_sc), for 1000 W/m² solar radiation, of these solar cells depend on the window layers, and vary in the range, 130-310 mV and 0.5-5 mA/cm², respectively. The typical fill factors (FF) of these cells are 0.25-0.42, and conversion efficiency, 0.1-0.4%.     

<Emphasis Type="Italic">In situ</Emphasis> fabrication of 2D SnS<Subscript>2</Subscript> nanosheets as a new electron transport layer for perovskite solar cells

To promote commercialization of perovskite solar cells (PSCs), low-temperature processed electron transport layer (ETL) with high carrier mobility still needs to be further developed. Here, we reported two-dimensional (2D) tin disulfide (SnS₂) nanosheets as ETL in PSCs for the first time. The morphologies of the 2D SnS₂ material can be easy controlled by the in situ synthesized method on the conductive fluorine-doped tin oxide (FTO) substrate. We achieved a champion power conversion efficiency (PCE) of 13.63%, with the short-circuit current density (J_SC) of 23.70 mA/cm², open-circuit voltage (V_OC) of 0.95 V, and fill factor (FF) of 0.61. The high J_SC of PSCs results from effective electron collection of the 2D SnS₂ nanosheets from perovskite layer and fast electron transport to the FTO. The low V_OC and FF are the results of the lower conduction band of 2D SnS₂ (4.23 eV) than that of TiO₂ (4.0 eV). These results demonstrate that 2D material is a promising candidate for ETL in PSCs.

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Effect of solution processed salt layers on the device performances of polymer solar cells

We report the solution processed Li salt layers (i.e. LiBF₄, and LiTFSI) in poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methylester (PCBM) bulk heterojunction solar cells, which facilitate electron injection at the interface between active layer and Al electrode. The Li salt layers are deposited on top of P3HT:PCBM active layer by simple drop-casting combined with controlled evaporation process. The solar cells employing Li salt layers exhibit the increase of short-circuit current (J_SC) and fill factor (FF) by 10% when compared with devices without such an injection layer, resulting in about 28% increase of power conversion efficiency. The effect of Li salt layers on the device performances is investigated with current–voltage (J–V) characteristics and impedance spectroscopy measurements.     

Design and fabrication of InxGa1 − xN/GaN solar cells with a multiple-quantum-well structure on SiCN/Si(111) substrates

The fabrication and characterization of In_xGa_1 − xN/GaN-based solar cells that use In_xGa_1 − xN multiple quantum wells (MQWs) and a SiCN/Si(111) substrate are reported. Solar cell operation with a low dark current density (J_d), a high open-circuit voltage (V_oc), a high short-circuit current density (J_sc), and a high fill factor (FF) is demonstrated. It was found that the proposed device and fabrication technology are applicable to the realization of solar cells with a low J_d of 2.14 to 8.88 μA/cm², a high V_oc of 2.72 to 2.92 V, a high J_sc of 2.72 to 2.97 mA/cm², and a high FF of 61.51 to 74.89%. The device performance with various quantum-well configurations was investigated under an air mass 1.5 global solar spectrum. A high photovoltaic efficiency of 5.95% in the MQW sample over the p-i-n sample was observed.     

Thin film CdZnS/CuInSe2 solar cells by spray pyrolysis

Cd_1−xZn_xS/CuInSe₂ solar cells having efficiencies in the range of 2·3% were fabricated by spray pyrolysis. The best cell had the following parameters:V _oc = 305 mV,J _sc = 32 mA/cm², FF = 0·32 area = 0·4 cm² and efficiency = 3·149%.V _oc versus temperature measurements showed that the electron affinity difference was 0·22 eV. Forward dark current versus voltage curves were plotted and a possible current mechanism occurring in these cells has been proposed.     

Physical properties of Bi doped CdTe thin films grown by CSVT and their influence on the CdS/CdTe solar cells PV-properties

The physical properties of Bi doped CdTe films, grown on glass substrates by the Closed Space Transport Vapour (CSVT) method, from different Bi doped CdTe powders are presented. The CdTe:Bi films were characterized using Photoluminescence, Hall effect, X-Ray diffraction, SEM and Photoconductivity measurements. Moreover, CdS/CdTe:Bi solar cells were made and their characteristics like short circuit current density (J_sc), open circuit voltage (V_OC), fill factor (FF) and efficiency (η) were determined. These devices were fabricated from Bi doped CdTe layers deposited on CdS with the same growth conditions than those used for the single CdTe:Bi layers. A correlation between the CdS/CdTe:Bi solar cell characteristics and the physical properties of the Bi doped CdTe thin films are presented and discussed.     

Charge transfer in blends of P3HT and colloidally prepared CuInS2 nanocrystals

CuInS₂ (CIS) is a suitable semiconductor for thin film photovoltaics and also a promising candidate to replace CdSe in hybrid polymer/nanoparticle solar cells, advantages being the lower toxicity and the better absorption properties. In this work, crystalline nanoparticles of CuInS₂ were successfully synthesized with uniform size and shape by means of colloidal chemistry. Photo-induced absorption spectroscopy was used to study charge transfer between poly(3-hexylthiophene) (P3HT) and the CIS nanoparticles. The appearance of signals corresponding to positive polarons provides evidence that charge transfer is possible in the P3HT/CIS system.