Search

Researchers are exploring the use of bio-based materials to enhance the performance and sustainability of solar cells. Bio-based materials can serve as both passive and active elements in solar cells. [...]

Researchers at UC Santa Barbara, Calif., developed a method to make high-quality perovskite films at room temperature. The new process simplifies the material's production process for use in solar cells [...]

Solar cells based on metal halide perovskites are one of the most promising photovoltaic technologies.sup.1-4. Over the past few years, the long-term operational stability of such devices has been greatly improved by tuning the composition of the perovskites.sup.5-9, optimizing the interfaces within the device structures.sup.10-13, and using new encapsulation techniques.sup.14,15. However, further improvements are required in order to deliver a longer-lasting technology. Ion migration in the perovskite active layer--especially under illumination and heat--is arguably the most difficult aspect to mitigate.sup.16-18. Here we incorporate ionic liquids into the perovskite film and thence into positive-intrinsic-negative photovoltaic devices, increasing the device efficiency and markedly improving the long-term device stability. Specifically, we observe a degradation in performance of only around five per cent for the most stable encapsulated device under continuous simulated full-spectrum sunlight for more than 1,800 hours at 70 to 75 degrees Celsius, and estimate that the time required for the device to drop to eighty per cent of its peak performance is about 5,200 hours. Our demonstration of long-term operational, stable solar cells under intense conditions is a key step towards a reliable perovskite photovoltaic technology. Addition of an ionic liquid, BMIMBF.sub.4, to metal halide perovskite solar cells improves their efficiency and long-term operation under accelerated aging conditions of high temperature and full-spectrum sunlight., Author(s): Sai Bai [sup.1] [sup.2] , Peimei Da [sup.1] , Cheng Li [sup.3] [sup.8] , Zhiping Wang [sup.1] , Zhongcheng Yuan [sup.2] , Fan Fu [sup.4] , Maciej Kawecki [sup.5] [...]

Many different photovoltaic technologies are being developed for large-scale solar energy conversion (1-4). The wafer-based first generation photovoltaic devices1 have been followed by thin-film solid semiconductor absorber layers sandwiched between two charge-selective contacts (3) and nanostructured (or mesostructured) solar cells that rely on a distributed heterojunction to generate charge and to transport positive and negative charges in spatially separated phases (4-6). Although many materials have been used in nanostructured devices, the goal of attaining high-efficiency thin film solar cells in such a way has yet to be achieved (7). Organometal halide perovskites have recently emerged as a promising material for high-efficiency nanostructured devices (8-11). Here we show that nanostructuring is not necessary to achieve high efficiencies with this material: a simple planar heterojunction solar cell incorporating vapour-deposited perovskite as the absorbing layer can have solar-to-electrical power conversion efficiencies of over 15 per cent (as measured under simulated full sunlight). This demonstrates that perovskite absorbers can function at the highest efficiencies in simplified device architectures, without the need for complex nanostructures., Within a solar cell there are many different components with discrete roles and having different tolerances for purity and optoelectronic properties. The hybrid inorganic-organic solar cell concept is 'material agnostic' [...]

A novel soluble conjugated polymers, P2, with coplanar thiophene-phenylene-thiophene unit is designed and synthesized as suitable active material used in tandem cells to compensate the poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C71 butyric acid methyl ester (P[C.sub.71]BM) bulk-heterojunction cell in this paper. P2 polymer bears advantages in both low optical bandgap (1.7 eV) and high hole mobility properties (3.4 x [10.sup.-3] [cm.sup.2]/V-s from field-effect transistor measurement). Furthermore, the electrochemical studies of P2 indicate desirable highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO/LUMO) band structure that enables a high open circuit voltage when pairing with PCBM acceptor. The best power conversion efficiency of this polymer solar cell thus far based on P2/P[C.sub.71]BM system with a weight ratio of 1:3 reached 4.4% with a short circuit current density ([J.sub.sc]) of 10.2 mA/[cm.sup.2], an open circuit voltage ([V.sub.oc]) of 0.81 V, and a fill factor (FF) of 0.53 under air mass (AM) 1.5 G (100 mW/[cm.sup.2]). The preliminary data of the tandem cell with indium tin oxide (ITO) glass/PEDOT:PSS/P2:P[C.sub.71]BM/TiOx/PEDOT:PSS/P3HT:P[C.sub.71]BM/TiOx/Al configuration has reached [J.sub.sc] of 6.2 mA/[cm.sup.2], [V.sub.oc] of 1.33 V, FF of 0.56 and an overall efficiency of 4.6% under AM 1.5 G (100 mW/[cm.sup.2]). [DOI: 10.1115/1.4001150] Keywords: conducting polymer, solar cell, tandem

The influence of a dye adsorption solvent of an infrared organic dye (NK-6037) on solar cell performance was investigated in a mesoporous Ti[O.sub.2] dye-sensitized solar cell (DSC). Various types of alcohols and a mixture of ethanol and tertiary-butanol (t-butanol) were applied as dye adsorption solvents. It was confirmed that the species of dye adsorption solvent significantly influences the performance of a DSC. Decreasing the specific dielectric constant of the dye adsorption solvent caused the amount of dye adsorbed on the Ti[O.sub.2] photoelectrode to increase dramatically. It is suggested that the specific dielectric constant of the dye adsorption solvent influences the solvation state of the NK-6037 dye in the solvent, thus determining, for instance, whether the dye is in the monomer state or the aggregate state. Interestingly, solar cell performance was not linearly proportional to the adsorbed amount of dye but a precise optimum amount of adsorbed dye was required for the best performance of the DSC. The optimum amount of adsorbed dye was approximately 5.0 x [10.sup.-8] mol/[cm.sup.2] and it was obtained by using solvents having a dielectric constant of approximately 18. This condition was realized by 1-butanol, 2-propanol, and a mixture of ethanol and t-butanol with a volume ratio of 7:3. The best efficiency obtained for the DSC was 1.7%, using the optimum amount of the adsorbed infrared dye NK-6037. It is speculated that an excess of dye on the Ti[O.sub.2] photoelectrode accelerates the formation of H-type dye aggregates, resulting in a decrease in short circuit photocurrent ([J.sub.sc]) by unfavorable side reactions of electron loss. It is demonstrated that dye adsorption solvent selection is the critical factor in obtaining high performance in a DSC [DOI: 10.1115/1.4001171] Keywords: dye-sensitized solar cell, infrared organic dye, dye adsorption solvent

As a kind of Na-incorporating control method, NaF co-evaporation or soda-lime glass thin films (SLGTFs) are useful to improve the photovoltaic performance of Cu(In, Ga)[Se.sub.2] (CIGS) cells fabricated on low-Na substrates. X-ray diffraction (XRD) patterns and scanning electron microscope pictures demonstrate that the grain size of CIGS thin film is reduced with the addition of Na. In addition, a variance of the preferred orientation is found by XRD patterns in terms of SLGTF samples. By a use of 100 nm thick SLGTF as a Na source, the best CIGS solar cell with an efficiency of 13.42% has been obtained. [c] 2010 Optical Society of America OCIS codes: 160.6000, 310.6845.

In this study, the exciton lifetime images within the photoactive layers of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are revealed by confocal optical microscopy combined with the fluorescence module. The images reveal that the active layers during slow solvent evaporation provide 3D pathways for charge transport and the concentration gradient through the film which reflects the better cell performance. This technique offers a great help to investigate the 3D optical-physical property without destroying the blends. 10.1021/ac901992c

Spectroscopic ellipsometry has been successfully used to characterize the CdS/CdTe heterojunction solar cell deposited on TEC15 glass. The effects of copper treatment 077 the optical properties of a cadmium chloride treated photovoltaic device were investigated using ellipsometry. No changes in either the band gaps or critical points of CdTe layer were noticed as a result of copper treatment. The copper treated CdTe laver exhibited a higher refractive index in the visible and longer wavelengths ([less than or equal to]3 eV), as compared with the untreated layer. This was attributed to the increased disorder in the case of copper treated laver. [DOI: 10.1115/1.3097282]

Transparent counter electrodes were prepared on transparent conductive glass (TCG) substrates from a hexachloroplatinic acid ([H.sub.2]Pt[Cl.sub.6]) solution applying the thermal decomposition method in combination with the spin-coating deposition technique. The effect of the precursor concentration and the number of deposited platinum layers on the surface characteristics of the Pt films was examined, and the relation between those surface characteristics and the electrochemical properties of the corresponding modified Pt/TCG electrodes was defined. Four types of counterelectrodes were prepared, differing in the concentration of the [H.sub.2]Pt[Cl.sub.6] solution (0.03M and 0.15M) and in the number of Pt layers (one or two Pt layers); their performance as counterelectrodes was evaluated after their incorporation into dye-sensitized solar cells (DSSCs) employing a solid state redox electrolyte. The obtained results show that solar cells using counterelectrodes prepared from the 0.03M [H.sub.2]Pt[Cl.sub.6] solution and consisting of two Pt lavers (Pt032 electrode) exhibited the best performance characteristics (diffusion coefficient [D.sup.+][I.sub.3.sup.-] = 1.58 x [10.sup.-5] [cm.sup.2] [s.sup.-1], conversion efficiency [eta] = 2.16%, fill factor ff = 62.14%, and short circuit photocurrent [I.sub.sc] = 4.71 mA [cm.sup.-2]). The electrochemical behavior of the modified counterelectrodes is consistent with the surface characteristics of the Pt film that formed on the conductive glass substrate, which seems to be significantly affected by the adopted method and the adjusted experimental parameters (Pt concentration and number of Pt layers). Specifically, this type of electrodes beside their low roughness ([R.sub.q] = 11.5 nm), also presents a high complexity ([D.sub.f] = 2.3). As a result, for this kind of solid state DSSCs, the less rough but the more complex the Pt/TCG electrode surface, the higher the efficiency of the corresponding solar cells. Keywords: dye-sensitized solar cells, platinum counterelectrode, thermal decomposition method, spin-coating technique

In this paper, we reported an improved preparation of 1-methyl-3-propylimidazolium iodide (MPII), which was the alkylation reaction of n-propyl iodide and 1-methylimidazole under solvent-free conditions by Teflon-lined, stainless autoclaves. It was shown that the resulting MPII was high pure, the conversion rate of 1-methylimidazole was close to 100% and the procedure was simple and ecofriendly. Moreover, the apparent diffusion coefficients of triiodide and iodide in the mixture with different ratios of MPII and 3-methoxypropionitrile were demonstrated by cyclic voltammetry using a Pt ultramicroelectrode. The dye-sensitized solar cells with the electrolyte, which was composed of 0.13 M [I.sub.2], 0.10 M LiI, 0.50 M 4-tert-butylpyrdine in the mixture of 3-methoxypropionitrile and MPII (weight ratio 0.65:1), gave short circuit photocurrent density of 14.82 mA/[cm.sup.2], open-circuit voltage of 0.69 V, and fill factor of 0.66, corresponding to the photoelectric conversion efficiency of 6.73% at the illumination (AM 1.5, 100 mW/[cm.sup.2]). Keywords: 1-Methyl-3-propylimidazolium iodide; Synthesis: Autoclave: Dye-sensitized solar cell

As a result of developing wide bandgap InGaP double hetero structure tunnel junction for sub-cell interconnection, InGaAs middle cell lattice-matched to Ge substrate, and InGaP-Ge heteroface structure bottom cell, we have demonstrated 38.9% efficiency at 489-suns AM1.5 with InGaP/InGaP/Ge 3-junction solar cells by in-house measurements. In addition, as a result of developing a non-imaging Fresnel lens as primary optics, a glass-rod kaleidoscope homogenizer as secondary optics and heat conductive concentrator solar cell modules, we have demonstrated 28.9% efficiency with 550-suns concentrator cell modules with an area of 5445 [cm.sup.2]. In order to realize 40% and 50% efficiency, new approaches for novel materials and structures are being studied. We have obtained the following results: (1) improvements of lattice-mismatched InGaP/InGaAs/Ge 3-junction solar cell property as a result of dislocation density reduction by using thermal cycle annealing, (2) high quality (In)GaAsN material for 4- and 5-junction applications by chemical beam epitaxy, (3) 11.27% efficiency InGaAsN single-junction cells, (4) 18.27% efficiency InGaAs/GaAs potentially modulated quantum well cells, and (5) 7.65% efficiency InAs quantum dot cells. Keywords: Solar cells; High efficiency; III-V compounds; Multi-junction; Concentrator; New III-V-nitride materials; Quantum wells; Quantum dots

Rapid thermal processing (RTP) provides a way to rapidly heat substrates to an elevated temperature to perform relatively short duration processes, typically less than 2-3 min long. RTP can be utilized to minimize the process cycle time without compromising process uniformity, thus eliminating a bottleneck in [CuIn.sub.1-x][Ga.sub.x][Se.sub.2-y][S.sub.y] (CIGSS) module fabrication. Some approaches have been able to realize solar cells with conversion efficiencies close or equal to those for conventionally processed solar cells with similar device structures. A RTP reactor for preparation of CIGSS thin films on 10 cm X 10 cm substrates has been designed, assembled, and tested at the Florida Solar Energy Center's PV Materials Lab. This paper describes the synthesis and characterization of CIGSS thin-film solar cells by the RTP technique. Materials characterization of these films was done by scanning electron microscopy, x-ray energy dispersive spectroscopy, x-ray diffraction, Auger electron spectroscopy, electron probe microanalysis, and electrical characterization was done by current-voltage measurements on soda lime glass substrates by the RTP technique. Encouraging results were obtained during the first few experimental sets, demonstrating that reasonable solar cell efficiencies (up to 9%) can be achieved with relatively shorter cycle times, lower thermal budgets, and without using toxic gases. [DOI: 10.1115/1.2735349]

The dilute nitride (GaIn)(NAs) material system grown lattice matched to GaAs or Ge with a 1 eV band gap is an interesting material for the use in four-junction solar cells with increased efficiencies. As a result of its metastability, several challenges exist for this material system, which up to now limits the device performance. We performed nanostructural analysis in combination with photoluminescence characterization to optimize the metal organic vapor phase growth as well as the annealing conditions for the quaternary solar cell material. The optimum annealing conditions depend strongly on the In content of the quaternary material. Valence force field calculations of stable N environments in the alloy support the model that the N moves from a Ga rich environment realized during growth into an In rich environment upon annealing. Simultaneously, N induced strain fluctuations, which are detected in the N containing material upon growth, are dissolved and the device properties are improved. [DOI: 10.1115/1.2734568]

Results of a solar thermophotovoltaic (STPV) system study are reported. Modeling of the STPV module performance and the analysis of various parameters influencing the system are presented. The ways for the STPV system efficiency to increase and their magnitude are considered such as: improvement of the emitter radiation selectivity and application of selective filters for better matching the emitter radiation spectrum and cell photoresponse; application of the cells with a back side reflector for recycling the sub-band gap photons; and development of low-band gap tandem TPV cells for better utilization of the radiation spectrum. Sunlight concentrator and STPV modules were designed, fabricated, and tested under indoor and outdoor conditions. A cost-effective sunlight concentrator with Fresnel lens was developed as a primary concentrator and a secondary quartz meniscus lens ensured the high concentration ratio of ~4000X, which is necessary for achieving the high efficiency of the concentrator--emitter system owing to trap escaping radiation. Several types of STPV modules have been developed and tested under concentrated sunlight. Photocurrent density of 4.5 A/c[m.sup.2] was registered in a photoreceiver based on 1 X 1 c[m.sup.2] GaSb cells under a solar powered tungsten emitter [DOI: 10.1115/1.2734576]

Solid-state dye-sensitized solar cells (DSSCs) were fabricated in which the thin p-CuI film acts as a hole collector. Influences of the different preparation methods, composition, aging time of the Ti[O.sub.2] pastes and sensitizing time on the performance of the cells were investigated. Different preparation routes for the Ti[O.sub.2] paste do not obviously affect the performance of the cells. The volume of water, acetic acid and 2-propanol contained in the Ti[O.sub.2] pastes and the amount of the Ti[O.sub.2] powder were determined. The efficiency of the cells remains nearly stable when the aging period of the Ti[O.sub.2] pastes is within one week. The favorable dying time is above 2 h. The cells having a favorable performance deliver a mean short-circuit photocurrent of ~10.8 mA [cm.sup.-2] and mean open-circuit voltage of 0.61 V at 100 mW [cm.sup.-2] (1.5 AM). The mean fill factor and the mean efficiency of these cells are ~0.55% and 3.7%, respectively. The short-circuit photocurrent rapidly decays after 3 h, and at the same time, the open-circuit voltage slowly decreases when the time increases, and then remains nearly stable after 24 h. Keywords: Solid-state solar cells; Titanium dioxide; Dye sensitization; CuI; Preparation conditions

Microwave conductivity is observed in Ti[O.sub.2] and Cul films at room temperature. Organic dye pyrogallor red is found to sensitize Ti[O.sub.2] and CuI in solid-state Ti[O.sub.2]|dye]CuI cells. Effect of ligands attached to crystal growth inhibitors on morphology of CuI films is studied. A weaker crystal growth inhibition was observed when size of ligands attached to surfactant is increased. Reasonable explanations are given for observed inhomogeneous photocurrent and its degradation under illumination. Keywords: Tripropylamine hydrothiocyanate; Pyrogallor red; Solid-state solar cell

For the working electrode of dye-sensitized solar cell (DSC), Ti[O.sub.2]/Si[O.sub.2] nanocomposite materials were electrodeposited on transparent fluorine doped tin oxide-coated glass by cathodic electrodeposition at room temperature. The electrode and DSC fabricated with Ti[O.sub.2]/Si[O.sub.2] nanocomposite were characterized with photocurrent density, X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM) and a photovoltaic performance test. On the electrodeposition, the addition of an appropriate amount of Si[O.sub.2] in the bath containing Ti[O.sub.2] slurry was essential to achieve the superior crystallinity, photocurrent density and photovoltaic performance of the resulting Ti[O.sub.2]/Si[O.sub.2] electrode, which was significantly superior to a bare Ti[O.sub.2] electrode. This enhanced performance of optimized Ti[O.sub.2]/Si[O.sub.2] electrode was ascribed to the role of Si[O.sub.2] as an energy barrier, increasing the physical separation of injected electrons and oxidized dyes/redox couple, and thereby retarding the recombination reactions in the resulting DSC. Keywords: Dye-sensitized solar cell; Electrodeposition; Ti[O.sub.2]Si[O.sub.2] nanocomposite; Energy barrier

Si-wafers for solar cells were cast in a size of 50 x 46 x 0.5 [mm.sup.3] by a direct casting method. A graphite mold coated by boron nitride (BN) powder was used in order to prevent the reaction between carbon and the molten silicon. Without any coating, the reaction of the Si melt to the graphite mold was very severe. In the case of BN coating, SiC was formed in the shape of tiny islands on the surface of the Si wafer by the reaction between the Si-melt and the carbon of the graphite mold at high temperature. The grain size was about 1 mm. The efficiency of the Si solar cell was about 0.5% under AM1.5 conditions. It was lower than that of a Si solar cell fabricated with a common single- (sc, 3.0%) and poly-crystalline (pc, 1.0%) Si wafer, which showed much lower efficiency than that of other commercial pc- or sc-Si solar cell (10-15%). Keywords: Silicon wafer; Direct casting; BN coating; Si solar cell

Crystalline silicon solar cells show promise for further improvement of cell efficiency and cost reduction by developing process technologies for large-area, thin and high-efficiency cells and manufacturing technologies for cells and modules with high yield and high productivity. In this paper, Japanese activities on crystalline Si wafers and solar cells are presented. Based on our research results from crystalline Si materials and solar cells, key issues for further development of crystalline Si materials and solar cells will be discussed together with recent progress in the field. According to the Japanese PV2030 road map, by the year 2030 we will have to realize efficiencies of 22% for module and 25% for cell technologies into industrial mass production, to reduce the wafer thickness to 50-100 [micro]m, and to reduce electricity cost from 50 Japanese Yen/kWh to 7 Yen/kWh in order to increase the market size by another 100-1000 times. Keywords: Crystalline silicon; Solar cell

Ti[O.sub.2] thin films were prepared on electrochemically etched porous Si by anodic oxidative hydrolysis of Ti[Cl.sub.3] for the purpose of solar cell application. We compared electrochemical and photoelectrochemical properties of the Ti[O.sub.2]-deposited porous Si electrodes (Ti[O.sub.2]/porous Si) with those of a porous Si electrode. The Ti[O.sub.2]/porous Si showed prolonged stability of photoluminescence and enhancements of photovoltage and photocurrent by 0.13 V and 67% increase, respectively, in comparison with porous Si due to the reduction of surface traps for charge carriers in the presence of Ti[O.sub.2] thin layer. [Li.sup.+] and [Na.sup.+] ions exhibited intercalation and deintercalation through the electrodeposited Ti[O.sub.2] film.

CuIn[Se.sub.2] thin films were prepared by a three-stage sequential co-evaporation of In-Se, Cu-Se, and In-Se elements for photovoltaic application. After growing CuIn[Se.sub.2] films, the film surface was converted to an ordered vacancy compound (Cu[In.sub.3][Se.sub.5]). The presence of a Cu[In.sub.3][Se.sub.5] layer on the CuIn[Se.sub.2] surface was confirmed by XRD and AES. By the. formation of the Cu[In.sub.3][Se.sub.5] phase on the CuIn[Se.sub.2] surface, the absorption edge was shifted from 1200 [Angstrom] to a shorter wavelength. On the CIS films, an [In.sub.2][Se.sub.3] buffer layer instead of the commonly known CdS layer was employed and deposited in the same evaporator without breaking the vacuum system. The ITO/ZnO/[In.sub.2][Se.sub.3]/CuIn[Se.sub.2] cells with a thin Cu[In.sub.3][Se.sub.5] layer at the [In.sub.2][Se.sub.3]/CuIn[Se.sub.2] interface yielded a solar efficiency of 8.46% with an active area of 0.2 [cm.sup.2] which is considered high efficiency regarding no Ga in the CIS absorber layer.

Microcrystalline silicon is a possible candidate for use in thin-film solar cells and other thin-film electronic devices. Both the photoconductivity and the ambipolar diffusion length in coplanar geometry can be computed if the values found in micro-c-Si:H samples are of the same order or higher than in a-Si:H. Specifically, for a dilution series of silane into hydrogen, the microcrystalline sample produced with the highest dilution has improved photoconductivity and ambipolar diffusion length in contrast to the amorphous sample of the same series at high generation rates.