Performance characteristics of polymer photovoltaic solar cells with an additive-incorporated active layer

We have investigated the performance characteristics of bulk-heterojunction polymer solar cells based on poly(3-hexylthiophene-2,5-diyl) and [6,6]-phenyl C₆₁ butyric acid methyl ester by adding 1,8-octanedithiol as a processing agent in an active layer. The effects of the additive, 1,8-octanedithiol, on the device performance parameter characteristics have been discussed. The current density-voltage measurements, UV-Vis absorption spectra, X-ray diffraction spectra, and scanning probe microscope images have been used to discuss the performance characteristics of polymer solar cells.     

Ultraviolet-ozone-treated PEDOT:PSS as anode buffer layer for organic solar cells

ABSTRACT: Ultraviolet-ozone-treated poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)was used as the anode buffer layer in copper phthalocyanine (CuPc)/fullerene-based solar cells. The power conversion efficiency of the cells with appropriated UV-ozone treatment was found to increase about 20% compared to the reference cell. The improved performance is attributed to the increased work function of the PEDOT:PSS layer, which improves the contact condition between PEDOT:PSS and CuPc, hence increasing the extraction efficiency of the photogenerated holes and decreasing the recombination probability of holes and electrons in the active organic layers.     

染料敏化纳米晶薄膜太阳能电池用染料敏化剂的研究进展

染料敏化剂的性能是影响染料敏化太阳能电池光电转化效率的重要因素,关于染料敏化剂的研究是当前研究的热点之一。本文简要介绍了染料敏化剂在染料敏化纳米晶太阳能电池中的作用以及各种染料敏化剂的优缺点及发展现状,并对其应用前景进行了展望。     

Morphology linked to miscibility in highly amorphous semi-conducting polymer/fullerene blends

Molecular miscibility is a defining property of mixtures of electron-donating polymers and electron-accepting fullerenes used in the photoactive layer of bulk heterojunction (BHJ) organic solar cells. Even though miscibility of fullerene in the polymer is a commonly observed property, quantitative measurements have unknown connections with other morphological properties such as domain size and domain purity. By varying the amount of fullerene loading in BHJ thin films, we show that morphological properties are related to miscibility via straightforward relationships. In particular, miscibility influences the sensitivity of domain spacing to fullerene loading and determines the domain volume fractions and the residual fullerene content in the mixed polymer-rich phase in devices. Not only does this work show the relationships between miscibility and morphology, but it also highlights the general importance in determining miscibility levels in BHJ systems in order to target optimum morphologies and domain purities.     

Semitransparent inverted polymer solar cells employing a sol-gel-derived TiO2 electron-selective layer on FTO and MoO3/Ag/MoO3 transparent electrode

We report a new semitransparent inverted polymer solar cell (PSC) with a structure of glass/FTO/nc-TiO₂/P3HT:PCBM/MoO₃/Ag/MoO₃. Because high-temperature annealing which decreased the conductivity of indium tin oxide (ITO) must be handled in the process of preparation of nanocrystalline titanium oxide (nc-TiO₂), we replace glass/ITO with a glass/fluorine-doped tin oxide (FTO) substrate to improve the device performance. The experimental results show that the replacing FTO substrate enhances light transmittance between 400 and 600 nm and does not change sheet resistance after annealing treatment. The dependence of device performances on resistivity, light transmittance, and thickness of the MoO₃/Ag/MoO₃ film was investigated. High power conversion efficiency (PCE) was achieved for FTO substrate inverted PSCs, which showed about 75% increase compared to our previously reported ITO substrate device at different thicknesses of the MoO₃/Ag/MoO₃ transparent electrode films illuminated from the FTO side (bottom side) and about 150% increase illuminated from the MoO₃/Ag/MoO₃ side (top side).     

Hybrid morphology dependence of CdTe:CdSe bulk-heterojunction solar cells

A nanocrystal thin-film solar cell operating on an exciton splitting pattern requires a highly efficient separation of electron-hole pairs and transportation of separated charges. A hybrid bulk-heterojunction (HBH) nanostructure providing a large contact area and interpenetrated charge channels is favorable to an inorganic nanocrystal solar cell with high performance. For this freshly appeared structure, here in this work, we have firstly explored the influence of hybrid morphology on the photovoltaic performance of CdTe:CdSe bulk-heterojunction solar cells with variation in CdSe nanoparticle morphology. Quantum dot (QD) or nanotetrapod (NT)-shaped CdSe nanocrystals have been employed together with CdTe NTs to construct different hybrid structures. The solar cells with the two different hybrid active layers show obvious difference in photovoltaic performance. The hybrid structure with densely packed and continuously interpenetrated two phases generates superior morphological and electrical properties for more efficient inorganic bulk-heterojunction solar cells, which could be readily realized in the NTs:QDs hybrid. This proved strategy is applicable and promising in designing other highly efficient inorganic hybrid solar cells.     

Fiber laser annealing of brush-painted ITO nanoparticles for use as transparent anode for organic solar cells

We report on a fiber laser annealing process for brush-painted ITO nanoparticles, for use as transparent anodes in cost-efficient printable organic solar cells (OSCs). By simple brushing of ITO nanoparticle ink onto glass substrates followed by direct fiber laser annealing, we fabricated solution-processed ITO anodes with a sheet resistance of 56.79 Ω/square and an optical transmittance of 85.77%. The electrical, optical, and structural properties of ITO nanoparticle electrodes were investigated as a function of laser scan speed under a nitrogen ambient. In addition, the detailed microstructure of the laser-annealed ITO electrode was examined to explain the conduction mechanism. OSCs fabricated on laser-annealed ITO electrodes exhibit an open circuit voltage of 0.59 V, short circuit current of 9.02 mA/cm², fill factor of 53.30%, and power conversion efficiency of 2.81%. Successful operation of those OSCs with laser-annealed ITO electrode indicates that fiber laser annealing is a simple and cost-effective option to replace conventional energy-intensive furnace-based annealing processes.     

Multi-alkylthienyl appended porphyrins for efficient dye-sensitized solar cells

Four porphyrin dyes, incorporating multi-alkylthienyl appended porphyrins as the electron donor, the 2-cyanoacrylic acid as the electron acceptor, and different π-conjugated spacer, have been synthesized for dye-sensitized solar cells (DSSCs). All the porphyrin dyes studied in this work exhibit red-shifted and broadened electronic spectra respect to the reference P_Zn as expected. By the introduction of thienyl groups at the meso-positions, the energy level of E_ox (excited-state oxidation potentials) is significantly shifted to the positive compared with the reference P_Zn, indicating a decreased HOMO-LUMO gap. The highest power conversion efficiency of the four dyes based on DSSCs reached 5.71% under AM 1.5 G irradiation.     

天然色素敏化纳米晶TiO_2太阳能电池研究

介绍了天然色素敏化纳米晶太阳能电池的制作过程。应用分光光度计对大量天然色素进行光谱表征,从中选择与太阳光匹配的光敏化剂,以提高太阳能电池的光电转化率及降低其成本。该电池在全色光的照射下,转化阳光为电能的效率达到2.1%。开路电压为0.53V,短路光电流为4.2mA/cm2。比较所测量到的太阳能电池的光电转换效率时,认为电子被氧化还原介质重捕获而无法有效输送限制了电池的效率。     

Effect of gold nanoparticles on the performances of TiO2 dye-sensitised solar cell

TiO₂ blended with Au nanoparticles (NP) was hydrothermally synthesised under controlled conditions and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). The dye-sensitised solar cells (DSSC) were characterized using the UV–vis spectrometry and current-voltage (I-V) testing. The performance of TiO₂-Au DSSC is significantly higher than TiO₂ DSSC. The addition of Au NPs improves the light harvesting efficiency of the DSSC, thus improving the short circuit current density, J_sc, and the conversion efficiency of the DSSC. The excitation of localised surface plasmon resonance of the Au nanoparticles utilised the strong local field enhancement around the Au NPs to increase the absorption in the surrounding TiO₂ layer. It was demonstrated that the power conversion efficiency of the DSSC was improved by 28% with the addition of Au NPs.     

Donor-acceptor liquid crystalline conjugated cooligomers for the preparation of films with the ideal morphology for bulk heterojunction solar cells

A series of novel donor-acceptor (D-A) liquid crystalline conjugated cooligomers, i.e. F3T4-epP, F4T6-epP and F5T8-epP, which comprise oligo(fluorene-alt-bithiophene)s (OFbTs) with the different lengths as the donor segments and a perylene diimide (PDI) derivative as the acceptor segment, were designed and synthesized. The cooligomers can form the films with the desired ideal morphology for bulk heterojunction (BHJ) polymer solar cells (PSCs). That means the films comprise ordered alternating D-A lamellae perpendicular to the substrates. Most importantly, the periods of the nanostructures can be tuned by varying molecular length and post-treatment condition. For F3T4-epP and F4T6-epP, the periods are close to the single and double molecular lengths upon thermal and solvent vapor annealing, respectively. However, only the nanostructures with the period close to the single molecular length were formed for F5T8-epP for both annealing processes. Solar cells based on above nanostructured films were fabricated to demonstrate the advantages of the ideal morphology for BHJ solar cells. It was found that the power conversion efficiency (PCE) of the devices was dependent on the molecular length and the order of the films. Solvent vapor annealed films exhibited the highest order therefore gave the best device performance. A PCE of 1.75% was demonstrated with the solvent vapor annealed films of F5T8-epP. This performance represents the best among the solar cells based on the single molecular materials.     

Tuning of defects in ZnO nanorod arrays used in bulk heterojunction solar cells

With particular focus on bulk heterojunction solar cells incorporating ZnO nanorods, we study how different annealing environments (air or Zn environment) and temperatures impact on the photoluminescence response. Our work gives new insight into the complex defect landscape in ZnO, and it also shows how the different defect types can be manipulated. We have determined the emission wavelengths for the two main defects which make up the visible band, the oxygen vacancy emission wavelength at approximately 530 nm and the zinc vacancy emission wavelength at approximately 630 nm. The precise nature of the defect landscape in the bulk of the nanorods is found to be unimportant to photovoltaic cell performance although the surface structure is more critical. Annealing of the nanorods is optimum at 300°C as this is a sufficiently high temperature to decompose Zn(OH)₂ formed at the surface of the nanorods during electrodeposition and sufficiently low to prevent ITO degradation.     

Tailoring side chains of low band gap polymers for high efficiency polymer solar cells

High efficiency organic solar cells (OSCs) require conjugated polymers with a low band gap, broad absorption in visible and IR region, high carrier mobility, and relatively high molecular weight as p-type donor materials. Flexible side chains on the rigid polymer backbone are crucial for the solubility of conjugated polymers. In this work, four polymers with the main chain structure of fluorene-thiophene-benzothiadiazole-thiophene and flexible side chains located on fluorene, thiophene, and benzothiadiazole moiety, respectively, have been synthesized by Suzuki-Miyaura-Schlüter polycondensation. Photovoltaic device measurements with a device configuration of ITO/polymer:PC₇₁BM blends/LiF/Al show that P1 carrying octyloxy chains on benzothiadiazole rings gives the best performance, with a power conversion efficiency of 3.1%.     

Nanostructured conformal hybrid solar cells: a promising architecture towards complete charge collection and light absorption

We introduce hybrid solar cells with an architecture consisting of an electrodeposited ZnO nanorod array (NRA) coated with a conformal thin layer (<50 nm) of organic polymer-fullerene blend and a quasi-conformal Ag top contact (Thin/NR). We have compared the performance of Thin/NR cells to conventional hybrid cells in which the same NRAs are completely filled with organic blend (Thick/NR). The Thin/NR design absorbs at least as much light as Thick/NR cells, while charge extraction is significantly enhanced due to the proximity of the electrodes, resulting in a higher current density per unit volume of blend and improved power conversion efficiency. The NRAs need not be periodic or aligned and hence can be made very simply.     

有机太阳能电池材料研究进展

对有机太阳能电池（Organic Solar Cells,OSCs）的研究背景、基本结构与原理进行了简单介绍。主要针对具有代表性的OSCs材料做了系统综述,并对该领域的发展进行了展望。     

Synthesis of a novel alkylimidazolium iodide containing an amide group for electrolyte of dye-sensitized solar cells

A novel alkylimidazolium iodide containing an amide group, 1-(2-hexanamidoethyl)-3-methylimidazol-3-ium iodide (amido-ImI), was synthesized to act as the quasi-solid-state electrolyte of dye-sensitized solar cells (DSSCs). The DSSC with the amido-ImI electrolyte exhibited short-circuit photocurrent density (J_sc) and overall energy conversion efficiency (η) that were improved by 7.2% and 10.2%, respectively, compared to those obtained with the cell containing 1-hexyl-2,3-dimethylimidazolium iodide, a commonly used liquid electrolyte, at 100 mW cm⁻². Furthermore, the stability of the DSSC was enhanced by the presence of amido-ImI.     

染料敏化太阳电池中光阳极的研究进展

染料敏化太阳电池(dye-sensitized solar cell,DSC)的光阳极作为其重要的组成部分,在近些年的研究中取得了较大的进展。常用作光阳极的氧化物包括TiO2、ZnO、SnO2、Nb2O5、A12O3等,其中,TiO2因为综合性能表现突出,成为主要研究的光阳极材料。特别是TiO2纳晶薄膜的性质、形貌、结构等均会对DSC光电性能产生较大影响,其性质调节主要通过表面处理、修饰、掺杂等手段,而不同形貌纳米TiO2的研究主要表现在一维结构上,如纳米线、纳米棒等,本文就这些方面的研究情况进行简单归纳总结,分析影响电池性能的关键因素,并对如何更全面、更深入的提高DSC光电性能作简要展望。     

Dinaphtho-s-indacene-based copolymers for inverted organic solar cells with high open-circuit voltages

We report on the synthesis and characterization of a series of donor–acceptor copolymers (PF1, PF2, PF3 or PF4) based on a dinaphtho-s-indacene (DNI) donor unit and four different acceptor units. The molecular weights of the copolymers were determined by using gel permeation chromatography, and their electrochemical properties were investigated by cyclic voltammetry. All four copolymers showed deep-lying highest occupied molecular orbital energy levels. Inverted bulk heterojunction solar cells were fabricated by using the synthesized copolymers as the electron donor material and 6,6-phenyl-C71-butyric acid methyl ester (PC₇₁BM) as the electron acceptor material. Inverted solar cells based on PF1:PC₇₁BM (1:4, w/w) exhibited a power conversion efficiency (PCE) of 3.07%, a high open-circuit voltage (V_oc) of 0.99 V, a short-circuit current density (J_sc) of 7.85 mA/cm², and a fill factor of 39.5% under the AM1.5G illumination. With the same fabrication method, the inverted devices based on PF2, PF3 and PF4 showed PCEs of 2.62, 1.18 and 1.32%, and V_oc values of 0.97, 0.91 and 0.80 V, respectively.     

Adsorption characteristics of Ru(II) dye on carbon nanotubes for organic solar cell

We present a study on the adsorption properties of ruthenium(II) dye (Ru(II) dye) on multi-walled carbon nanotubes (MWNTs). To fabricate dye sensitized solar cells (DSCs) using dye coated MWNTs, we have developed a method to form covalently linked adducts of MWNTs and Ru(II) dye. MWNTs were functionalized by sonication in hydrogen peroxide solution. Ru(II) dye can be attached to the functionalized MWNTs by a synthetic route using Thionyl chloride (SOCl₂) followed by ethylenediamine. The adsorption characteristics were affected by parameters such as chemical oxidation of MWNTs, sonication process, processing temperature and time. The amount of adsorbed Ru(II) dye was effectively affected by treatment temperature of SOCl₂ than any other parameters.