Application In Hybrid Solar Cells Research Articles

Three-dimensional morphology of CuInS2:P3HT hybrid blends for photovoltaic applications

Despite potential advantages, the performance of hybrid solar cells with colloidal nanocrystals remains low compared to pure organic solar cells, in particular, when Cd- and Pb-free nanocrystals are employed. To understand this discrepancy, we analyzed possible limiting factors of the performance of hybrid solar cells with CuInS2 nanoparticles and the polymer poly(3-hexylthiophene) (P3HT). Optimizing the thickness of the active layer indicated that charge transport limits the performance of the solar cells. Since charge transport is among others influenced by the morphology of the bulk heterojunction layer, we performed a detailed analysis of the blend morphology. Therefore, we used electron tomography which provides three-dimensional information on the interpenetrating network formed by the hybrid CuInS2:P3HT system. Using statistical methods, we analyzed the distribution of the nanoparticles inside the polymer matrix and the structure of the percolation paths. We found that the morphology appears well suited for application in hybrid solar cells, meaning that other factors must be the bottleneck. Therefore, we investigated in a second step the influence of a post-deposition ligand exchange with acetic acid. This strategy resulted in a strong relative improvement of the solar cell performance, although absolute performance parameters remain low in comparison to hybrid solar cells with colloidal cadmium or lead chalcogenide nanocrystals.

Characterization of amphiphilic block-copolymers constituted of a low band gap rigid segment (PCPDTBT) and P4VP based coil block synthesized by two different strategies

Two homologous series of rod-coil block-copolymers, composed by a low band gap rod moiety (poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b:3.4-b’]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)], PCPDTBT) and a flexible poly(4-vinylpyridine) based polar block, were synthesized by two different approaches. Step Growth-like procedure provided copolymers with longer coil, whilst copolymers with longer rod arise from Chain Growth-like process. Both the series were deeply investigated with different analytical techniques (1H NMR, SEC-DV, and MALDI-TOF MS) in order to prove the coupling process and elucidate the composition of the obtained materials. Chemical composition was evaluated by 1H NMR analysis. DSC heating traces of rod-coil copolymers synthesized by Step Growth-like route present two well resolved glass transition temperatures corresponding to the rod and coil blocks. The low band-gap rod-coil block copolymers especially these with short coil can find application in hybrid solar cells.

Formation of porous SnS nanoplate networks from solution and their application in hybrid solar cells.

Herein, we present a facile solution-based route towards nanostructured, hybrid absorber layers based on tin mono-sulfide (SnS), an emerging, non-toxic absorber material for low-cost and large-scale PV applications. Charge photogeneration properties in the hybrid system are studied using transient absorption spectroscopy and fabricated solar cells show efficient photocurrent generation over a broad spectral range.

Comparative Study on Planar-silicon and Nano-silicon Si/PCBM Inorganic-organic Hybrid Junctions

Inorganic-organic heterojunction devices based on organic polymer and inorganic semiconductors has attracted extensive attention for high performance hybrid solar cell applications, due to the combined advantage of high carrier mobility of inorganic semiconductors and easy processing, strong absorption of organic polymers. In this study, both planar-Si and nano-Si were combined with spin-coated (6, 6)-phenyl C61-butyric acid methyl ester (PCBM) organic film to form Si/PCBM inorganic/organic hybrid junctions. A comparative study was per- formed through quantitative electrical analysis of planar-Si/PCBM and nano-Si/PCBM, respectively. In general, both devices exhibited a rectifying diode-like behavior. However, a higher turn-on voltage and smaller current density were observed from nano-Si/ PCBM junctions, which was in contradiction with the expectation from the view of junction area. The corresponding mechanisms were further investigated with measurements of impedance spectroscopy (IS). Our results indicated that this abnormal electrical characteristic of nano-Si/PCBM compared with normal p-n junction was highly associated with the parasitic effects caused by the defect states at the junc- tion interface.

ZnO nanorod arrays pre-coated with DCJTB dye for inverted type hybrid solar cells incorporating P3HT donor

This paper reports the utilization of a fluorescent dye, 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetra-methyljulolidyl-9-enyl)-4H-pyran (DCJTB) as the surface modifier of ZnO nanorods for inverted type hybrid solar cell application. The DCJTB solution with concentrations of 10 and 15 mM was spin-coated onto the ZnO nanorod arrays grown on the fluorine-doped tin oxide glass substrate pre-coated with ZnO seed layer. The poly(3-hexylthiophene-2,5-diyl) (P3HT) as electron donor was then spin-coated onto ZnO nanorod arrays, followed by the deposition of silver as anode using magnetron sputtering technique. A large portion of pre-coated DCJTB has been redissolved and washed out in the subsequent P3HT spin coating process. Nevertheless, the increase in hydrophobicity of ZnO nanorod arrays pre-coated with DCJTB leads to improved interfacial compatibility between ZnO nanorods and P3HT. As a result, the enhanced exciton dissociation efficiency at the ZnO nanorods/P3HT interfaces results in the increment of short circuit current density and open circuit voltage. In addition, DCJTB residue covering the FTO exposed area could reduce the hole leakage current from P3HT to FTO, hence resulting in higher open circuit voltage. The device with the optimum DCJTB pre-coating concentration of 10 mM exhibited almost two times increase in power conversion efficiency as compared to that of pristine device.

Molecular‐Level Switching of Polymer/Nanocrystal Non‐Covalent Interactions and Application in Hybrid Solar Cells

Hybrid composites obtained upon blending conjugated polymers and colloidal semiconductor nanocrystals are regarded as attractive photo­active materials for optoelectronic applications. Here it is demonstrated that tailoring nanocrystal surface chemistry permits to control non‐covalent and electronic interactions between organic and inorganic components. The pending moieties of organic ligands at the nanocrystal surface are shown to not merely confer colloidal stability while hindering charge separation and transport, but drastically impact morphology of hybrid composites during formation from blend solutions. The relevance of this approach to photovoltaic applications is demonstrated for composites based on poly(3‐hexylthiophene) and lead sulfide nanocrystals, considered as inadequate until this report, which enable the fabrication of hybrid solar cells displaying a power conversion efficiency that reaches 3%. By investigating (quasi)steady‐state and time‐resolved photo‐induced processes in the nanocomposites and their constituents, it is ascertained that electron transfer occurs at the hybrid interface yielding long‐lived separated charge carriers, whereas interfacial hole transfer appears hindered. Here a reliable alternative aiming to gain control over macroscopic optoelectronic properties of polymer/nanocrystal composites by mediating their non‐covalent interactions via ligands' pending moieties is provided, thus opening new possibilities towards efficient solution‐processed hybrid solar cells.

The origin of efficiency enhancement of inorganic/organic Hybrid solar Cells by robust samarium phosphate nanophosphors

An effective energy level regulation of acceptor by doping samarium phosphate nanophosphors (SmPO4 NPs) was reported for inorganic/organic hybrid solar cell applications. SmPO4 NPs doped TiO2/P3HT bulk heterojunction (BHJ) solar cell shows an enhanced power conversion efficiency of approaching 3% as compared with that of its counterpart without SmPO4 NPs (1.98%). The underlying photophysical mechanism was probed by applying femtosecond transient absorption spectroscopy and the results show that the efficiency enhancement was ascribed to the improved hot electron, less energetic electron, hole transports at the interface of BHJ apart from down-conversion photoluminescence of SmPO4 NPs. It has been evidenced that the hot electron transfer life time was shortened by more than 40% (i.e., from τhot-e=30.2 to 17.9ps) than pure TiO2 acceptor while the hole transfer lifetime was boosted by almost 20% (i.e., from 6.92 to 5.58ns). Such charge carrier improvements stem from the efficient energy level regulations by SmPO4 NPs. In detail, the conduction band (CB) edge of TiO2 has been elevated by 0.57eV while the valence band (VB) edge has been elevated by 0.32eV, thus not only narrowing down the energy offset between CB energy levels of acceptor TiO2 and donor P3HT, but also meanwhile enlarging the band gap of TiO2 itself that permits to inhibit electron-hole recombination within TiO2. This work demonstrates that samarium ions can efficiently facilitate exciton generation, dissociation and charge transport and have an important role in enhancing photovoltaic performance.

A strategy to stabilise the local structure of Ti4+ and Zn2+ species against aging in TiO2/aluminium-doped ZnO bi-layers for applications in hybrid solar cells

We explore a strategy to counteract aging issues in TiO2/aluminium-doped ZnO bi-layers used in hybrid solar cells photo-anodes, mainly related to Zn diffusion in the TiO2 matrix. Different Ti4+ and Zn2+ local structures within the anatase grains and along the film thickness were found as a function of post-deposition annealing treatments in the range between 200 °C and 500 °C by synchrotron radiation extended x-ray absorption fine structure analyses. In particular, in the 500 °C-treated sample, diffusion of zinc species along the TiO2 grain-boundaries has been observed with aging (3 years). In contrast, a mild thermal budget at 200 °C favours a proper atomic arrangement of the zinc-containing anatase lattice which reduces Zn diffusion, thus guaranteeing a good stability with aging.

Stabilizer-free CdSe/CdS core/shell particles from one-step solution precipitation and their application in hybrid solar cells

CdSe/CdS core/shell nanoparticles were synthesized in aqueous solution by one-step process. CdSe precipitates were first obtained at 80 °C in a solution of cadmium chloride, sodium citrate, ammonia and sodium selenosulfate. After 4 h of reaction, the solution with CdSe products was cooled to 60 °C and thiourea (TU), a sulfur precursor, was added while stirring. The amount of the TU solution added was 2, 5 and 10 mL, and the obtained products were named as CdSe/CdS-2, CdSe/CdS-5 and CdSe/CdS-10, respectively. It is observed that CdSe core particles had predominantly a crystalline cubic structure, and the addition of TU in the CdSe solution led to the formation of a very low concentration of hexagonal crystalline phase of CdS whose intensity increased with the amount of TU. The energy-dispersive X-ray spectroscopy in a scanning electron microscope indicated an increase of sulfur concentration in CdSe/CdS products as a function of the amount of TU solution. The presence of CdS-like morphology on the surface of CdSe/CdS particles was also evident. Photoluminescence emission spectra of the CdSe/CdS particles exhibited an increasing CdS emission as the volume of TU solution increased. The photovoltaic performance of solar cells based on CdSe/CdS particles and poly(3-hexylthiophene) (P3HT) suggested that the CdSe particles should be surrounded by CdS because of the similarity between the current–voltage curves of CdSe/CdS/P3HT heterojunctions and that of CdS/P3HT solar cells.

Solution synthesized CdS nanoparticles for hybrid solar cell applications

Nanocrystalline semiconductor materials have attracted considerable attention due to their particle size dependent physical properties and very large specific surface area that are not present in bulk materials. Usually they are synthesized with organic ligands to disperse them from agglomeration. However, these ligands could act as series resistance in the active layer of solar cells. In this work cadmium sulfide (CdS) precipitates were prepared from cadmium and sulfide ion solutions without any ligands at different solution temperature and synthesis time. The obtained CdS precipitates were washed by rinsing with methanol or by centrifugation with water and methanol. By using Fourier transform infrared spectroscopy (FTIR) impurities were observed on the surface of rinsed CdS samples and they had been eliminated after washing by centrifugation. X-ray diffraction (XRD) patterns indicate that the obtained products were of hexagonal structure. The average size of the CdS crystallites observed by transmission electron microscopy was of about 6 nm before centrifugal washing and 3 nm after washing. The band-gap (E g ) values of CdS particles were between 2.44 and 2.56 eV, estimated by the Tauc relation using the Kubelka–Munk expression for the absorption coefficient. Photoluminiscent spectra of the centrifugal washed CdS samples indicate the presence of surface states that probably were charge recombination centers in CdS:poly(3-hexylthiophene) hybrid solar cells. The best cell prepared with CdS nanoparticles showed a photocurrent (J sc ) of 2.2 mA/cm2 and a photovoltage (V oc ) of 0.84 V, measured in air at room temperature under 100 mW/cm2 illumination in a solar simulator.

Nanoimprinted Comb Structures in a Low Bandgap Polymer: Thermal Processing and Their Application in Hybrid Solar Cells

In this paper, we investigate conjugated polymer layers structured by nanoimprint lithography toward their suitability for the fabrication of nanostructured polymer/metal sulfide hybrid solar cells. Consequently, we first study the thermal stability of the nanoimprinted conjugated polymer layers by means of scanning electron microscopy and grazing incidence small-angle X-ray scattering, which reveals a reasonable thermal stability up to 145 °C and sufficient robustness against the solvent mixture used in the subsequent fabrication process. In the second part, we demonstrate the preparation of nanostructured polymer/copper indium sulfide hybrid solar cells via the infiltration and thermal decomposition of a mixture of copper and indium xanthates. Although this step needs temperatures of more than 160 °C, the nanostructures are retained in the final polymer/copper indium sulfide layers. The nanostructured solar cells show significantly improved power conversion efficiencies compared to similarly prepared flat bilayer devices, which is based on a distinct improvement of the short circuit current in the nanostructured solar cells.

Nanostructured Films of Conjugated Polyelectrolytes: Fundamental Studies and Application in Hybrid Solar Cells

Conjugated polyelectrolytes (CPEs) are semiconduciting organic polymers that feature polar/ionic solubilizing groups. We have demonstrated that CPEs can be used as light absorbing sensitizers atop nanocrystalline TiO2 in a dye-sensitized solar cell configuration leading to relatively efficient light-to-electrical power conversion. We have observed interesting corrleations between polymer chain length (degree of polymerization, DP) and solution state (molecularly dissolved vs. aggregated) on the DSSC efficiency. In order to better understand the interaction of CPEs with the metal-oxide interface, we have investigated the interaction of CPEs with single crystal TiO2 interfaces using high resolution atomic force microscopy imaging and photocurrent spectroscopy. Results of this work will be presented, with an emphasis on the fundamental factors that control the interaction and charge injection efficiency of CPEs at TiO2 interfaces.

Multi-branched CdSe nanocrystals stabilized by weak ligand for hybrid solar cell application.

In this article, multi-branched CdSe nanocrystals were produced by a facile colloidal approach stabilized by oleylamine at a relative low temperature. The as-prepared multi-branched CdSe nanocrystals after simple washing process were used in the fabrication of poly(3-hexylthiophene)/CdSe bulk heterojunction photovoltaic device. The effective charge separation in the poly(3-hexylthiophene)/ CdSe nanocomposites have been confirmed by the strong photoluminescence quenching. The films of the blends of P3HT and simply-washed CdSe nanocrystals show more uniform morphology and flatter surface than the film of the bends of P3HT and pyridine-refluxed CdSe nanocrystals. The corresponding power conversion efficiency under 1 sun is about 0.66% for the P3HT/pyridine-washed CdSe hybrid device. Our work did a preliminary study in the hybrid solar cell application of branched blenze CdSe nanocrystals prepared by an easier way, and will be interesting and helpful for making the high-efficiency hybrid solar cells with branched CdSe acceptors.

Low-temperature growth of well-aligned ZnO nanowire arrays by chemical bath deposition for hybrid solar cell application

Well-aligned ZnO nanowire arrays were grown on indium tin oxide coated glass substrates by a facile chemical bath deposition technique. Morphologies, crystalline structure and optical transmission were investigated by field-emission scanning electron microscope, X-ray diffraction and UV–visible transmission spectrum, respectively. The results showed that ZnO nanowires were aligned in a dense array approximately perpendicular to substrate surface, they were wurtzite-structured (hexagonal) ZnO. In addition, the nanowire arrays exhibited high optical transmission (>85 %) in the visible region. Furthermore, an inverted inorganic/polymer hybrid solar cell was built using as-grown well-aligned ZnO nanowire arrays as inorganic layer, under the AM 1.5 illumination with a light intensity of 80 mW/cm2, the device showed an open circuit voltage (Voc) of 0.44 V, a short circuit current (Jsc) of 3.23 mA/cm2, a fill-factor of 38 %, and a power conversion efficiency of 0.68 %.

In situ syntheses of semiconducting nanoparticles in conjugated polymer matrices and their application in photovoltaics.

AbstractHybrid solar cells based on conjugated polymers and inorganic semiconducting nanoparticles combine beneficial properties of organic and inorganic semiconductors and are, therefore, an exciting alternative to pure organic or inorganic solar cell technologies. Several approaches for the fabrication of hybrid solar cells are already elaborated and explored. In the last years routes have emerged, where the nanoparticles are prepared directly in the matrix of the conjugated polymer. Here, the conjugated polymer prevents the nanoparticles from excessive growth and thereby makes additional capping agents obsolete. This review focuses on in situ preparation methods of inorganic semiconducting nanoparticles in conjugated polymers in view of applications in hybrid solar cells. The details, advantages and disadvantages of the different in situ methods are critically examined and put in comparison to the classical route where pre-synthesized nanoparticles are used. Various key factors influencing the solar cell performance as well as future strategies for increasing the overall efficiency of hybrid solar cells prepared via in situ routes are discussed.

Cadmium Sulfide Nanoparticles Synthesized by Microwave Heating for Hybrid Solar Cell Applications

Cadmium sulfide nanoparticles (CdS-n) are excellent electron acceptor for hybrid solar cell applications. However, the particle size and properties of the CdS-n products depend largely on the synthesis methodologies. In this work, CdS-n were synthetized by microwave heating using thioacetamide (TA) or thiourea (TU) as sulfur sources. The obtained CdS-n(TA) showed a random distribution of hexagonal particles and contained TA residues. The latter could originate the charge carrier recombination process and cause a low photovoltage (Voc, 0.3 V) in the hybrid solar cells formed by the inorganic particles and poly(3-hexylthiophene) (P3HT). Under similar synthesis conditions, in contrast, CdS-n synthesized with TU consisted of spherical particles with similar size and contained carbonyl groups at their surface. CdS-n(TU) could be well dispersed in the nonpolar P3HT solution, leading to aVocof about 0.6–0.8 V in the resulting CdS-n(TU) : P3HT solar cells. The results of this work suggest that the reactant sources in microwave methods can affect the physicochemical properties of the obtained inorganic semiconductor nanoparticles, which finally influenced the photovoltaic performance of related hybrid solar cells.

Influence of Cathode Work Functions on the Photovoltaic Properties of MEH-PPV: TiO<sub>2</sub> Bulk Heterojunction Solar Cell

Bulk heterojunction solar cell has received significant attention over the past decade due to low cost power generation and the potential to develop a clean renewable energy source [. We investigated the effect of different type of metal cathodes on the power conversion efficiency of bulk heterojunction solar cell based on a blend of conjugated polymer poly [2-methoxy 5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) with titanium dioxide (TiO2). In this case of study, Aluminum (Al) and gold (Au) has been chosen as the metal cathode due to the difference of work function and their wide application in hybrid solar cell. We show that the choice of metal cathode plays a role in determining overall device efficiency through their impact on short-circuit current, open circuit voltage and fill factor due to the influence of work function. It is found that the device employing Al metal cathode which has low work function is showing a comparable performance to the Au metal electrode with fill factor of over 20 % and a power conversion efficiency of 3.3x10-3 %. Overall it is demonstrated that the matching between the work function of the cathode and photoactive layer MEH-PPV: TiO2 is the most important factor towards best bulk heterojunction solar cell performance.

Fabrication and application in hybrid solar cell of ZnO nanorod arrays

Well-aligned ZnO nanorod arrays (ZNRAs) were grown on coated indium tin oxide coated glass substrates from aqueous solutions at low temperature. Morphologies, crystalline structure and optical transmission were investigated by a scanning electron microscope, X-ray diffraction and UV–Visible transmission spectra, respectively. The results showed that ZNRAs grew vertically from the substrates, having uniform thickness and length distribution, ZnO nanorods were wurtzite-structured (hexagonal) ZnO. The high optical transmission in the visible region was also achieved. Furthermore, a hybrid solar cell was be constructured using ZNRAs as inorganic layer, and a power conversion efficiency of 0.47 % was achieved.

International Conference on Solar Energy Photovoltaics

Worldwide, the interest in photovoltaics as an energy technology as well as an industrial opportunity has increased significantly within the last few years, and with the launch of Jawaharlal Nehru National Solar Mission (JNNSM) it has created a lot of interest in the Indian solar sector. To create demand and attract investment in the sector, the government is providing various incentives. India has a huge potential for solar PV and with the right policy support by the Indian Government, India can become a major player in the solar market globally. The conference was a great success, having 3 keynote lectures, 5 plenary lectures, 12 invited lectures, and 90 contributed papers.The conferencewas inaugurated byMr. Arun Kumar Sahoo, Minister of State, Energy, and I&PR, Government of Odisha, India who emphasizes on energy Security. The guest of honour, Padma Shri Professor A. K. Barua, discussed the status and prospects of solar photovoltaics in India. The conference mainly focuses on device aspects of photovoltaic, involving nearly all the area with a special session on plasmonics and nanostructerd solar cells. The selected papers for this special issue are representative of the presentation/deliberation during the International Conference on Solar Energy Photovoltaic held at KIIT University, Bhubaneswar, India from 19th to 21st December, 2012. The special issue has papers focused on alternative buffer layer for polycrystalline thin film solar cells to replace CdS (cadmium sulfide). The focused materials were SnS (tin sulfide) and In 2 S 3 (indium sulfide). Few articles emphasize the use of transparent conducting oxide (TCO) for the hybrid and organic solar cell applications. Recently, the focus has been shifted to the use of cheap and abundant elements that make CZTS (copper zinc tin sulfide) as a promising alternative to current solar cells [1, 2]. Few papers have discussed the preparation of CZTS film using low-cost techniques. Some articles discuss the formation of nanoinks and nanopartilces of CIS (copper indium selenide) and CdSe. The conference was well supported by the Department of Science and Technology (DST) through its Solar Energy Research Initiative Program, Defence Research and Development Organization (DRDO), Indian Space Research Organization (ISRO), and Hind High Vacuum Pvt. Ltd. Special thanks go to the Founder of KIIT University, Dr. Achutya Samantawho has encouraged and guided us tomake this conference a great success.

Protic Ionic Liquids as p-Dopant for Organic Hole Transporting Materials and Their Application in High Efficiency Hybrid Solar Cells

Chemical doping is a powerful method to improve the charge transport and to control the conductivity in organic semiconductors (OSs) for a wide range of electronic devices. We demonstrate protic ionic liquids (PILs) as effective p-dopant in both polymeric and small molecule OSs. In particular, we show that PILs promote single electron oxidation, which increases the hole concentration in the semiconducting film. The illustrated PIL-doping mechanism is compatible with materials processed by solution and is stable in air. We report the use of PIL-doping in hybrid solar cells based on triarylamine hole transporting materials, such as 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9'-spirobifluorene (spiro-OMeTAD). We show improved power conversion efficiency by replacing lithium salts, typical p-dopants for spiro-OMeTAD, with PILs. We use photovoltage-photocurrent decay and photoinduced absorption spectroscopy to establish that significantly improved device performance is mainly due to reduced charge transport resistance in the hole-transporting layer, as potentiated by PIL-doping.