Nanocomposite Solar Cells Research Articles

Effect of UV-activated TiO2 Nanoparticles on the Properties and Performance of PAni-TiO2 Nanocomposite Films for Solar Cell Applications

To improve the performance of organic solar cells by enhancing the properties of the photoactivated nanocomposite layer, the UV irradiation process was used to activate titanium dioxide nanoparticles (TiO2 NPs). Herein, polymer solar cells were fabricated with FTO/(PAni-TiO2)/Ag system. A series of mixed polyaniline (PAni) with 20% of activated TiO2 NPs at different processing times was used to form PAni-TiO2 nanocomposite films. The structural evolution, surface characteristics, optical and electrical properties of PAni-TiO2 films have been investigated. XRD patterns showed that the UV treatment of TiO2 NPs increased the crystallite from 18.35 to 24.1 nm and the degree of crystallinity increased by 5.6%. The irradiated PAni-TiO2 films showed a rougher and more porous surface compared to the untreated one. Moreover, the adhesion force and electrical conductivity of the treated nanocomposite films at 8 h improved to be 137 mN/m and 6.62 S/m, respectively. Incorporation of activated TiO2 NPs exposure to UV for different times from 0 to 8 h with the PAni matrix enhanced the current density (Jsc) of PAni-TiO2 based nanocomposite solar cells from 3.11 to 4.83 (mA/cm2) and their efficiency from 0.33 to 0.85%. The increase in the solar cell efficiency is mostly ascribed to a structural change accompanied by a rapid increase in surface roughness, which led to a decrease in the reflected photons and thus an increase in the charge carriers produced. These results revealed the effect of surface UV irradiation of TiO2 NPs on their structural properties and the electronic contact between PAni and TiO2 NPs, which greatly influenced the amount of carrier transport within the PAni-TiO2 composites.

Nanocomposite solar cells based on organic/inorganic (clonidine/Si) heterojunction with plasmonic Au nanoparticles

The peculiarities of optical and electrical properties of organic(clonidine)/inorganic(Si) heterojunction with plasmonic Au nanoparticles have been investigated by reflection spectra, photoelectric and current-voltage characteristics measurements. Porous nanostructured surfaces of silicon wafers were obtained by the method of selective chemical etching initiated by metal (gold) nanoparticles. Nanocomposites based on nanostructured silicon, clonidine and gold nanoparticles have been made. Two types of structure, namely, solar cells and photodiodes on the basis of such heterojunction were analysed. The reflection spectra of light confirmed the excitation of the plasmon mode in nanocomposites with gold nanoparticles. Photoelectric studies have shown an increase of the photocurrent of solar cells obtained as a result of using both nanostructured silicon and gold nanoparticles in 1.5 and 7 times, respectively. Study of the injection properties of the structures showed that the clonidine layer always facilitates the injection of current carriers, while gold nanoparticles limit the current in the case of a flat surface.

Fabrication of TiO2-CuInS2 nanocomposite on ITO substrate via liquid carbon dioxide coating

TiO2-CuInS2 is one of the promising materials for 3D nanocomposite solar cells. To utilize for 3D nanocomposite solar cells, TiO2-CuInS2 should well deposited onto transparent conducting oxide such as indium doped tin oxide (ITO). High pressure coating with liquid carbondioxide (l-CO2) was successfully deposited TiO2-metals chalcogenide onto ITO substrate. Further heat treatment (oxidation and sulfurization) lead the formation of CuInS2 from metals chalcogenide deposited on the mesoporous TiO2. The formation of CuInS2 on the was confirmed by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD) and Raman spectroscopy. The atomic ratios of deposited CuInS2 were nearly stoichiometric after sulfurization. The crystal growths of CuInS2 were controlled by adjusting the number of coating cycles.

A comparison of copper indium sulfide-polymer nanocomposite solar cells in inverted and regular device architecture

In this study, the influence of device architecture (regular versus inverted) and different interlayers on performance and lifetime of polymer-nanocrystal hybrid solar cells is explored. The absorber layers of the investigated solar cells consist of the low band gap conjugated polymer poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl] (PCDTBT) and copper indium sulfide (CIS) nanocrystals. These are prepared directly in the polymer matrix via an in situ approach using copper and indium xanthates, which are converted to CIS nanocrystals by mild thermal annealing. Different interlayers – poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) and inorganic metal oxides (V2O5, MoO3) – are used as hole extraction layers between absorber and anode. All three layers were successfully applied in solar cells in regular architecture. Using an inverted device design, a PEDOT:PSS interlayer and Ag electrodes, open circuit voltages of 550mV could be obtained, which are comparable to values obtained with solar cells having easily oxidizing low work function metal electrodes. However, inverted solar cells with a V2O5 hole extraction layer could not be obtained due to possible incompatibility of the V2O5 coating process with the underlying absorber layer. In the case of MoO3 interlayers, the introduction of additional layers led to working inverted solar cells.

The Effect of Structural Properties of Cu2Se/Polyvinylcarbazole Nanocomposites on the Performance of Hybrid Solar Cells

It has been said that substitution of fullerenes with semiconductor nanocrystals in bulk heterojunction solar cells can potentially increase the power conversion efficiencies (PCE) of these devices far beyond the 10% mark. However new semiconductor nanocrystals other than the potentially toxic CdSe and PbS are necessary. Herein we report on the synthesis of Cu2Se nanocrystals and their incorporation into polyvinylcarbazole (PVK) to form polymer nanocomposites for use as active layers in hybrid solar cells. Nearly monodispersed 4 nm Cu2Se nanocrystals were synthesized using the conventional colloidal synthesis. Varying weight % of these nanocrystals was added to PVK to form polymer nanocomposites. The 10% polymer nanocomposite showed retention of the properties of the pure polymer whilst the 50% resulted in a complete breakdown of the polymeric structure as evident from the FTIR, TGA, and SEM. The lack of transport channels in the 50% polymer nanocomposite solar cell resulted in a device with no photoresponse whilst the 10% polymer nanocomposite resulted in a device with an open circuit voltage of 0.50 V, a short circuit current of 7.34 mA/cm2, and a fill factor of 22.28% resulting in a PCE of 1.02%.

Correlation between nanostructural, optical, and photoelectrical properties of P3HT:SiNW nanocomposites for solar‐cell application

Hybrid organic/inorganic nanocomposite solar cells are a potential candidate as an alternative to photovoltaic (PV) devices based on semiconducting inorganic or organic nanomaterials. In a recent study, carried on ITO/PVK:n‐TiO2/Al structures, we have observed a performance degradation due to bipolar charge recombination and space‐charge formation. Then, a simulation of I–V characteristics of photovoltaic (PV) diodes for different organic nanomaterials suggested replacing poly (N‐vinylcarbazole) (PVK) by poly (3‐hexylthiophene‐2,5‐diyl) P3HT. In this work, we have studied the current–voltage characteristics of ITO/PEDOT:PSS/P3HT:SiNW/Al solar cell under white illumination with different volume ratios (10%, 20%, 50%) of SiNW. The results have shown a maximum FF for 20% silicon nanowire (SiNW) volume ratio corresponding on the one hand to the morphology exhibiting the lowest RMS and on the other hand the maximum quenching of PL spectra. A degradation of the PV properties is induced at higher composition by the formation of larger of SiNW aggregates. Procedures have been developed to extract the different parameters from I–V characteristics under illumination in the basis of an equivalent circuit. The variation of the photogenerated current with SiNW volume ratios confirms that the PV response is optimum for 20 vol% SiNW.

Influence of the bridging atom in fluorene analogue low‐bandgap polymers on photophysical and morphological properties of copper indium sulfide/polymer nanocomposite solar cells

ABSTRACTThis contribution presents the correlation between structural, morphological, and fluorescence properties as well as device performance of nanocomposite solar cells comprising two low‐band gap polymers, poly[[9‐(1‐octylnonyl)−9H‐carbazole‐2,7‐diyl]‐2,5‐thiophenediyl‐2,1,3‐benzothiadiazole‐4,7‐diyl‐2,5‐thiophenediyl] (PCDTBT) and poly[2,1,3‐benzothiadiazole‐4,7‐diyl‐2,5‐thiophenediyl(9,9‐dioctyl‐9H‐9‐silafluorene‐2,7‐diyl)−2,5‐thiophenediyl] (PSiF‐DBT) and copper indium sulfide (CIS). It shows that, in analogy to organic solar cells, the device efficiency is strongly determined by different polymer structures leading to a different packing of the polymer chains and consequently to diverse morphologies. X‐ray diffraction investigation indicates increased semicrystallinity in PSiF‐DBT compared with the nitrogen analogue PCDTBT. The photoluminescence (PL) quenching of this polymer indicates that the higher photogeneration achieved in PSiF‐DBT based films can be correlated to a favorable donor‐acceptor phase separation. Transmission electron microscopy studies of PCDTBT:CIS blended films suggest the formation of polymer agglomerates in the layer resulting in a decreased PL quenching efficiency. For the considered polymer:CIS system, the combination of these effects leads to an enhanced overall device efficiency. © 2013 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2013, 51, 1400–1410

Comprehensive Investigation of Silver Nanoparticle/Aluminum Electrodes for Copper Indium Sulfide/Polymer Hybrid Solar Cells

Electrode materials are primarily chosen based on their work function to suit the energy levels of the absorber materials. In this paper, we focus on the modification of aluminum cathodes with a thin silver interlayer (2 nm) in copper indium sulfide/poly[(2,7-silafluorene)-alt-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)] (PSiF-DBT) nanocomposite solar cells, which improves the fill factor compared to pure aluminum electrodes. A comprehensive structural investigation was performed by means of transmission electron microscopy and time-of-flight secondary ion mass spectrometry revealing the presence of silver nanoparticles in an aluminum oxide matrix between the absorber layer and the aluminum cathode. In combination with complementary optical investigations, the origin of the improvement is ascribed to a facilitated charge extraction.

A Direct Route Towards Polymer/Copper Indium Sulfide Nanocomposite Solar Cells

Polymer/copper indium sulfide (CIS) nanocomposite solar cells are prepared via a capper free in situ preparation route using copper and indium xanthates as precursors, which decompose and form CIS nanoparticles in the polymer matrix during a mild thermal treatment. The solar cells generate current in a wide range of the solar spectrum and exhibit efficiencies up to 2.8%.

CuInS 2–Poly(3-(ethyl-4-butanoate)thiophene) nanocomposite solar cells: Preparation by an in situ formation route, performance and stability issues

In this contribution we present an in situ method for the preparation of CuInS 2–poly(3-(ethyl-4-butanoate)thiophene) (P3EBT) nanocomposite layers and their application in nanocomposite solar cells. A precursor solution containing copper and indium salts, thiourea and the conjugated polymer was prepared in pyridine, which was coated onto glass/ITO substrates followed by a heating step at 180 °C. The heating step induced the formation of the CuInS 2 nanoparticles homogeneously dispersed in the conjugated polymer matrix. The formation of the nanocomposite was investigated in situ by X-ray scattering techniques and TEM methods showing that nano-scaled CuInS 2 was formed. By addition of small amounts of zinc salt to the precursor solution, zinc containing CuInS 2 (ZCIS) was formed. ZCIS–P3EBT active layers exhibited higher V OC than CuInS 2–P3EBT layers and showed efficiencies of about 0.4%. Additionally the stability of the solar cells was tested over a time scale of 172 h.

Efficient hybrid polymer/titania solar cells sensitized with carboxylated polymer dye

A facile method to prepare polymer-TiO 2 hybrid nanocomposite based solar cells has been developed. Here a fabrication method to make the nanocrystalline TiO 2 layer from commercial TiO 2 powder using a simple approach is reported. Active layers were prepared in a thickness range from 0.3 to 1.8 μm with this method. We also demonstrate its use to obtain efficient organic-inorganic hybrid nanocomposite solar cells giving photovoltaic current density as high as 4.5 mA/cm 2 and power conversion efficiency of 0.79%. Commercially available conjugated polymers such as poly[3-(5-carboxypentyl)thiophene-2,5-diyl] (P3HT-COOH) as sensitizer, poly(3-hexylthiophene) (P3HT) as hole conducting layer and conducting poly[3,4-(ethylenedioxy)-thiophene]:poly(styrene sulfonate) (PEDOT:PSS) as charge collection layer have been used. Effect of annealing on the solar cell performance is studied in correlation to the morphology of the nanocomposite as well as absorption in active layers.

Surface Passivation of Nanoporous TiO2 via Atomic Layer Deposition of ZrO2 for Solid-State Dye-Sensitized Solar Cell Applications

We report here the utilization of atomic layer deposition to passivate surface trap states in mesoporous TiO2 nanoparticles for solid-state dye-sensitized solar cells based on 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD). By depositing ZrO2 films with angstrom-level precision, coating the mesoporous TiO2 produces over a two-fold enhancement in short-circuit current density, as compared to a control device. Impedance spectroscopy measurements provide evidence that the ZrO2 coating reduces recombination losses at the TiO2/spiro-OMeTAD interface and passivates localized surface states. Low-frequency negative capacitances, frequently observed in nanocomposite solar cells, have been associated with the surface-state mediated charge transfer from TiO2 to the spiro-OMeTAD.

Nanocomposite solar cells: the requirement and challenge of kinetic charge separation

Nanocrystalline solar cells promise significant advantages with respect to cost-efficient mass production, since they do not require imprinted chemical potential gradients for charge separation (e.g., electrical fields generated by p, n doping, which should last for one to three decades). They, however, require kinetic charge separation and chemical electronic mechanisms, which rectify photocurrents for energy conversion. Such mechanisms are presently not well understood, since the existing nanosolar cells (dye and polymer solar cells) have evolved largely empirically. It is shown in this paper that function and properties of kinetically determined solar cells can be derived from irreversible thermodynamic principles considering minimum entropy production (or the principle of least action) and involve solid-state electrochemical processes. Based on this model, presently studied nanosolar cells and also the primary photosynthetic mechanism are analyzed to identify the most significant physical–chemical factors involved.

Highly Efficient Solar Cells Based on Poly(3-butylthiophene) Nanowires

Poly(3-butylthiophene) (P3BT) nanowires, prepared by solution-phase self-assembly, have been used to construct highly efficient P3BT/fullerene nanocomposite solar cells. The fullerene/P3BT nanocomposite films showed an electrically bicontinuous nanoscale morphology with average field-effect hole mobilities as high as 8.0 x 10(-3) cm2/Vs due to the interconnected P3BT nanowire network revealed by TEM and AFM imaging. The power conversion efficiency of fullerene/P3BT nanowire devices was 3.0% (at 100 mW/cm2, AM1.5) in air and found to be identical with our similarly tested fullerene/poly(3-hexylthiophene) photovoltaic cells. This discovery expands the scope of promising materials and architectures for efficient bulk heterojunction solar cells.

Dynamics of Charge Separation and Trap-Limited Electron Transport in TiO2 Nanostructures

The dynamics of charge separation and transport in metal-oxide nanostructures used in nanocomposite solar cells is measured by time-resolved surface photovoltage (SPV) and described by random walk numerical simulations (RWNS). Characteristic features of anomalous diffusion and trap-limited electron transport are observed in SPV transients measured on a porous TiO2 layer sensitized with N3 dye molecules. RWNS carried out on a three-dimensional cubic lattice with an exponential distribution of states can describe these transients quantitatively over many orders of magnitude in time. The RWNS reproduce the main experimental features and permit us to extract the microscopic parameters governing electron transport such as the characteristic trap energy and the screening length.

Low-cost 3D nanocomposite solar cells obtained by electrodeposition of CuInSe 2

Thin CuInSe 2 films have been prepared by electrodeposition from a single bath aqueous solution on both dense and nanoporous TiO 2. The films are deposited potentiostatically using a N 2-purged electrolyte at different potentials. Various deposition times and solution compositions have been employed. The effect of annealing in air and in argon at different temperatures and times is also investigated. Thin films and nanocomposites of TiO 2 and CuInSe 2 have been studied with electron microscopy, X-ray diffraction, Raman spectroscopy, and optical absorption spectroscopy. After a thermal anneal in argon at 350 °C for 30 min excellent CuInSe 2 is obtained. In particular the nominal crystal structure and the bandgap of 1.0 eV are found. Although pinholes are present occasionally, good samples with diode curves showing a rectification ratio of 24 at ±1 V are obtained. Upon irradiation with simulated solar light of 1000 W m −2 a clear photoconductivity response is observed. Furthermore, also some photovoltaic energy conversion is found in TiO 2|CuInSe 2 nanocomposites.

A parametric study of TiO2/CuInS2 nanocomposite solar cells: how cell thickness, buffer layer thickness, andTiO2 particle size affect performance

3D CuInS2/TiO2 nanocomposite solar cell performance is strongly influenced by several structuralfactors, including cell thickness, buffer layer thickness, and the morphology of theTiO2 nanoparticulate matrix. To delineate the effect of these structural factors on photovoltaic performance,a series of parametric studies are performed where a single structural parameter is varied(TiO2 nanoparticulatematrix thickness, In2S3 buffer layer thickness, or TiO2 particle size) while all other fabrication conditions are held constant. The bestoverall performance (3.0% efficiency at AM 1.5) is achieved from a device withTiO2 matrixthickness ≈200 nm,In2S3 buffer layerthickness ≈60 nm, and TiO2 nanoparticulate size = 300 nm. Notably, the film thickness in the best-performing cell (200 nm) is less than theTiO2 particle size (300 nm), corresponding to a discontinuous nanoparticulate film. ThickerTiO2 nanoparticulatefilms or smaller TiO2 particles sizes lead to decreased performance due to increased chargetransport resistance. However, the performance from a planar cell (where theTiO2 nanoparticulate layer is not used) is inferior to the performance from thebetter-optimized 3D cells, indicating that some degree of nanostructuringimproves performance. Device performance is also observed to depend strongly onIn2S3 buffer layer thickness, with optimal performance achieved for a buffer layerthickness of approximately 60 nm. The optimal buffer layer thickness is governedby two opposing factors: increasing the buffer layer thickness improves theinterfacial characteristics (as measured by decreasing leakage conductance,G) but also screens the incoming light and causes an increase in thecharge transport resistance (as measured by the cell series resistance,Rs).

Hybrid Solar Cells with Prescribed Nanoscale Morphologies Based on Hyperbranched Semiconductor Nanocrystals

In recent years, the search to develop large-area solar cells at low cost has led to research on photovoltaic (PV) systems based on nanocomposites containing conjugated polymers. These composite films can be synthesized and processed at lower costs and with greater versatility than the solid state inorganic semiconductors that comprise today's solar cells. However, the best nanocomposite solar cells are based on a complex architecture, consisting of a fine blend of interpenetrating and percolating donor and acceptor materials. Cell performance is strongly dependent on blend morphology, and solution-based fabrication techniques often result in uncontrolled and irreproducible blends, whose composite morphologies are difficult to characterize accurately. Here we incorporate three-dimensional hyperbranched colloidal semiconductor nanocrystals in solution-processed hybrid organic-inorganic solar cells, yielding reproducible and controlled nanoscale morphology.

The Influence of TiO2 Particle Size in TiO2/CuInS2 Nanocomposite Solar Cells

AbstractThe recently developed CuInS2/TiO2 3D nanocomposite solar cell employs a three‐dimensional, or “bulk”, heterojunction to reduce the average minority charge‐carrier‐transport distance and thus improve device performance compared to a planar configuration. 3D nanocomposite solar‐cell performance is strongly influenced by the morphology of the TiO2 nanoparticulate matrix. To explore the effect of TiO2 morphology, a series of three nanocomposite solar‐cell devices are studied using 9, 50, and 300 nm TiO2 nanoparticles, respectively. The photovoltaic efficiency increases dramatically with increasing particle size, from 0.2 % for the 9 nm sample to 2.8 % for the 300 nm sample. Performance improvements are attributed primarily to greatly improved charge transport with increasing particle size. Other contributing factors may include increased photon absorption and improved interfacial characteristics in the larger‐particle‐size matrix.

Nanocomposite organic solar cells continue to improve

Nanocomposite organic solar cells continue to improve