We report a solid-state dye-sensitized solar cell with a record efficiency of 4% under simulated sunlight (AM1.5global, 100mW/cm2). This was made possible by using a new amphiphilic dye with hydrophobic spacers in combination with spiro-OMeTAD. We attribute the significant improvement in the device performance to the self-assembly of the dye to form a compact layer on the TiO2 surface and to the hydrophobic chains working as blocking layer between spiro-OMeTAD and TiO2 to reduce the back electron transfer. In addition, we studied the influence of nanoporous TiO2 film thickness on the performance of the device. These results demonstrate the high potential for solid state dye sensitized solar cells to compete with amorphous silicon cells as low cost alternative.

CuInS2 films are often grown in a two-step process with the deposition of a Cu-In alloy followed by high temperature sulphurisation in either S vapour or H2 S. Numerous techniques exist for the deposition of Cu-In. In this work Cu-In films have been deposited on tin oxide coated glass using the electroless deposition technique, a low cost, low temperature approach. The films were found to consist of a two layered structure. Initially, Cu islands grew forming a layer on the substrate. The deposition process subsequently produced dendritic Cu-In alloys from the tops of the Cu islands. Various CuIn phases were observed, namely Cu9In4 and CuIn, the presence of which was related to the solution pH. None of the films were found to contain metallic In, indicating that this process may be well suited to subsequent high temperature sulphurisation.

The constant photocurrent method has been used to obtain the density of occupied electronic states of tritiated amorphous silicon thin films. The analyses showed a peak of defects located 1.24 eV below the conduction band edge, suggesting that the main type of defect present in the films was a doubly occupied dangling bond. The concentration of defect states increases as a result of tritium decay by about two orders of magnitude over a period of 500 hours. The defect density in the tritiated amorphous silicon samples could be reduced by thermal annealing, after which it increased once more.

GaxIn1−xAs and GayIn1−yP layers were grown lattice mismatched to GaAs and Ge by low-pressure metal organic vapor phase epitaxy (LP-MOPVE). These materials are very promising for further increasing the efficiency of monolithic triple-junction solar cells. Different buffer layer structures were realized. Transmission electron microscopy and x-ray diffraction analysis were used to characterize the quality of the crystal. Both linear and step-graded buffers in GaxIn1−xAs were successfully used under an active solar cell structure. GayIn1−yP as buffer material showed a worse performance. Excellent solar cell performance was achieved for lattice mismatched single-, dual- and triple-junction solar cells.

In a heterojunction photovoltaic device of ITO/TiO2/poly(3-alkylthiophene)/Au, the photocurrent was characterized with different temperature by using regio-random (P3HT), regular (RP3HT) poly(3-hexylthiophene) and regio-regular poly(3-dodecylthiophene)(RP3DT). The regio-regularity and alky chain length affected the photovoltaic characteristics due to the difference in the hole carrier transport. The drift charge mobility of those devices were analyzed by the space charge limited current (SCLC) theory using dark current versus bias relations. The photocurrent in the devices based on poly(3-alkylthiopene)s began to decrease rapidly below a temperature at which the drift charge mobility was 10−5 cm2/V.s.

The characteristics of 1 MeV electron irradiated GaAs solar cells grown on GaAs and Si substrates are studied under dark and AM 0 conditions. The short circuit currents (Isc) for GaAs/GaAs cell and GaAs/Si cell have been decreased at higher fluences. The degradation rate of Voc and Pmax for GaAs/Si is slower than that of GaAs/GaAs at the fluence 1×1016 cm−2. This is due to the high radiation resistance of saturation current. It has been due to slow generation of arsnic vacancies related defect (VAs) in the GaAs/Si solar cell, which is determined by photoluminescence analyses and deep level transient spectroscopy.

Antimony sulfide thin films (300 nm) have been deposited on glass substrates at 1–10°C from chemical bath. When heated these become crystalline and photoconductive with optical band gap (direct) of 1.7 eV. Thin films formed from chemical baths containing SbCl3 and sodium selenosulfate are of mixed phase Sb2O3/Sb2Se3, which when heated in the presence of Se-vapor converts to single phase Sb2Se3 film with optical band gap of 1.1 eV. Such films possess dark conductivity of 10-8 ohm-1cm-1 and show photosensitivity of two orders. Reaction of Sb2S3-CuS in nitrogen at 400°C produces crystalline, photoconductive p-type CuSbS2 with optical band gap (direct) of 1.5 eV. By controlling the deposition and heating condition, (i)Sb2S3-(p)CuSbS2 layer is formed, which is utilized in a photovoltaic structure, (n)CdS:In-(i)Sb2S3-(p)CuSbS2, with a Voc of 345 mV and Jsc 0.18 mA/cm2 under 1 kW m-2 tungsten halogen illumination. In the case of a structure, CdS:Cl-Sb2S3-Cu2-xSe, Voc of 350 mV and Jsc of 0.5 mA/cm2 are observed.

In this study highly-ordered titania nanotube arrays of variable wall-thickness and length are used to photocleave water under ultraviolet irradiation. We demonstrate that the wall thickness, and length, of the nanotubes can be controlled via anodization bath composition and temperature. The nanotube length and wall thickness are key parameters influencing the magnitude of the photoanodic response and the overall efficiency of the water-splitting reaction. For 22 nm inner-pore diameter nanotube-arrays 6 μm in length, with 9 nm wall thickness, upon 320–400 nm illumination at an intensity of 100 mW/cm2, hydrogen gas was generated at the power-time normalized rate of 51 mL/hr•W at an overall conversion efficiency of 12.5%. To the best of our knowledge, this hydrogen generation rate is the highest reported for a titania-based photoelectrochemical cell.

We report novel composite photovoltaics fabricated from nanoporous Si filled with Copper Phthalocyanine (CuPC) and its derivatives, including discotic liquid crystal CuPC. Porous n-type Si (PSi) was prepared electrochemically (pore size 10–20 nm) and filled with CuPC solution by impregnation under pressure or spin casting (liquid crystal CuPC) onto a porous surface followed by heating to the temperature of the mesophase transition. For porous layer with the thickness more than 1500–2000 nm, the conversion efficiency was up to 3% under a tungsten lamp with solar filters (30 mW/cm2). The porous structure and pore filling were examined by SEM and XPS techniques. Photocurrent spectra of the CuPC-PSi cell demonstrate two bands that correspond to the absorbance of the protonated form of CuPC. A comparative analysis between CuPC and liquid crystal CuPC has been made and conclusions about possible mechanisms of charge transfer and transport are drawn. The solar cell optimization is discussed as well.

Screen-printing is studied as deposition technique for conjugated material based layers. Photovoltaics based on the principle of bulk donor-acceptor heterojunction are tested using a blend of poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1, 4-phenylene vinylene) (MEH-PPV) mixed with the C60-derivative (6, 6)-phenyl C61-butyric acid methyl ester (PCBM). First, different solution concentrations of the donor MEH-PPV material and of the blend are subjected to rheology measurements. Addition of the acceptor (PCBM) to a donor material based solution induces a decrease of the solution viscosity. However, the overall flow behaviour of the blend remains similar to that of the MEH-PPV based solution. Secondly, it is shown that specific printer settings have to be used to obtain active layers that are suitable for opto-electronic applications. Finally, devices with an overall energy conversion efficiency of 1.25% under standardized simulated solar illumination (AM1.5G; 100mW/cm2) have been obtained showing that screen-printing can be a suitable technique for the deposition of the active layer of polymer solar cells.

The ability to dissociate the photo-generated excitons and transport the resulting charge carriers are the major impediments in improving the efficiency of polymeric solar cells. In order to simultaneously address both of these issues, we have investigated the use of quantum dotsingle wall carbon nanotube (QD-SWNT) complexes as a suitable nanomaterial dopant in these devices. The formation of CdSe-SWNT complexes occurred through covalent attachment of carboxylic acid-functionalized SWNTs with CdSe-aminoethanethiol (AET) quantum dots. An additional synthetic approach was evaluated using both electrostatic and covalent attachment schemes for CuInS2-mercaptoacetic acid (MA) quantum dots and amine terminated SWNTs. The efficacy of each approach is discussed, including the necessary transmission electron microscopy (TEM) and optical absorption spectroscopy data to probe the interactions between nanomaterials. The potential effects of charge transfer between components may have important implications in the efficiency of these materials for polymeric photovoltaic devices.

The various polymorphs of titanium oxide (TiO2) are probably the most widely studied materials for photovoltaic applications. It is well known that composition and particles size can have a profound effect on photoactivity. It is thought that high surface to volume nanostructures such as nanofibers and nanorods may possess the optimal properties. We have developed technology for the preparation of TiO2 nanofibers in a variety of forms including core shell structures, papers and films. The formation of mesoporous TiO2 fibers as spider webs and papers has been achieved by electrostatic deposition. The mesoporous fibers and other forms such as shaped particles and films have been employed as templates to grow TiO2 nanofibers in various configurations. The proposed research below will address the synthesis and characterization of the TiO2 fibers developed by these techniques

Coin-shaped multicrystalline Si1-xGex crystals were grown using a Brigdman method combined with die-casting growth. Si1-xGex alloy is known as a candidate material for producing Auger generation, which creates more than one electron/hole pair per absorbed photon. Since Si1-xGex alloy shows a complete series of solid solutions, precipitating crystals with a certain composition of silicon or germanium by conventional selective growth methods is burdensome. Using die-casting combined with Bridgman growth brought about Si1-xGex precipitation in a form completely different from that predicted by the Si-Ge phase diagram. By combining this growth with subsequent heat treatment of the precipitated Si1-xGex sample, Si1-xGex (x= 0.5 ± 3 %) could be obtained. Indirect band-gap energy was estimated by measuring room-temperature optical absorption coefficient of the grown samples.

The quarternary CIGS nanoparticles for absorber layer of solar cells have been synthesized with various mole ratios by colloidal route. The CIGS nanoparticles were prepared by reacting CuI, InI3, GaI3 in pyridine with Na2Se in methanol at 0°C under inert atmosphere. For Cu0.9In0.8Ga0.3Se2 and Cu0.9In0.7Ga0.4Se2 stoichiometric ratios, tube-type nanofibers were obtained with the widths in the range of 20–50 nm and lengths of 0.1–3 μm from reaction at 0°C for 20 min. For Cu1.1In0.68Ga0.23Se1.91, and Cu0.9In0.68Ga0.23Se1.91 ratios, spherical nanoparticles were obtained from the same reaction condition. As compared to particles from Cu0.9In0.68Ga0.23Se1.91 ratio, more uniform and smaller nanoparticles with diameter in the range of 5–20 nm were obtained from the Cu1.1In0.68Ga0.23Se1.91 stoichiometric ratio. The morphology change of the CIGS particles seems to be closely related to the ratio of Cu/(In, Ga).

Excimer laser crystallisation is used to fabricate nanocrystalline thin film silicon Schottky barrier solar cells, in a superstrate configuration with indium tin oxide as the front contact and chromium as the back contact. 150 nm thick intrinsic absorber layers are used for the solar cells, and was crystallised using an excimer laser with different laser energy densities. These layers were characterised using Raman spectroscopy and optical absorption before device fabrication. External quantum efficiencies of the devices were calculated from the spectral response data of the devices. A maximum efficiency of 70 % is observed for low energy irradiation, which is significant for very thin absorber layers. Device operation is discussed with proposed band structures for the devices and supplementary measurements.

High quality CdS thin films made with ultrasonic agitation during chemical bath deposition were investigated. The change in band gap and variation of atomic stacking during the film growth was observed as a function of bath pH. The band gap of as-deposited thin films of CdS was found to be between 2.26 eV and 2.50 eV, the highest being observed when the pH was 9.0. The transition from cubic (β-CdS) to hexagonal (a-CdS) was observed with decreasing pH. The lattice parameters of CdCl2 treated CdS were found to be a = 0.414 nm and c = 0.672 nm. Calculations based on the Sherrer formula showed significant grain growth after annealing with CdCl2. No apparent effect of ultrasonication on crystalline structure of CdS was seen in this method, although ultrasonication was noted to produce films with a higher quality optical surface. A maximum bath temperature was fixed at 70°C in order to suppress the rate of homogeneous reaction and minimise the evaporation of ammonia from the chemical bath.

Conventional two-dimensional p-n diodes can be used for betavoltaic and photovoltaic energy conversion, but the device efficiency is limited by the planar geometry. We propose and demonstrate a novel three-dimensional diode geometry based on porous silicon. The 3D pore array provides two very important features: (1) the storage of the radioisotope energy source and (2) its extreme proximity to the p-n junction on each pore wall. The particle energy losses are thereby minimized prior to entering the conversion layer. In betavoltaics, our 3D betavoltaic device efficiency is 10 times that of a similar planar device. In photovoltaics, photons play the role of beta particles and photon trapping inside the pores enhances the conversion efficiency. Further fabrication and geometry optimization can result in practical, high performance devices.

The monolithic integration of high efficiency III-V compound solar cell materials and devices with lower-cost, robust and scaleable Si substrates has been a driving force in photovoltaics (PV) basic research for decades. Recent advances in controlling mismatch-induced defects that result from structural and chemical differences between III-V solar cell materials and Si using a combination of SiGe interlayers and monolayer-scale control of III-V/IV interfaces, have led to a series of fundamental advances at the material and device levels, which establish that the great potential of III-V/Si PV is within reach. These include demonstrations of GaAs epitaxial layers on Si that are anti-phase domain-free with verified dislocation densities at or below 1×106 cm−2 and negligible interface diffusion, minority carrier lifetimes for GaAs on Si in excess of 10 ns, single junction GaAs-based solar cells on Si with open circuit voltages (Voc) in excess of 980 mV, efficiencies beyond 18%, and area-independent PV characteristics up to at least 4 cm2. These advances are attributed in large part to the use of a novel “engineered Si substrate” based on compositionally-graded SiGe buffers such that a high-quality, low defect density, relaxed, “virtual” Ge substrate could be developed that can support lattice-matched III-V epitaxy and thus merge III-V technology based on the GaAs (or Ge) lattice constant with Si wafers. This paper focuses on recent results that extend this work to the first demonstration of high performance III-V dual junction solar cells on SiGe/Si. Open circuit voltages in excess of 2 V at one-sun have been obtained for the conventionally “lattice-matched” In0.49Ga0.51P/GaAs dual junction cells on inactive, engineered SiGe/Si; to our knowledge is the first demonstration of > 2V solar power generation on a Si wafer. Comparisons with identical cells on GaAs substrates reveal that the Voc on engineered Si retains more than 94% of its homoepitaxial value, and that at present both DJ/GaAs and DJ/SiGe/Si cells are similarly limited by current mismatch in these early cells, and not fundamental defect factors associated with the engineered Si substrates.

Poly-Si thin films deposited at low temperature by using the metal-induced growth (MIG) method have the advantage of less metal impurity contaminations and relative large grains with preferred crystal orientation of (220). In recent research, the Schottky solar diode made of MIG poly-Si shows Jsc of 12 mA/cm2 and Voc of 0.214V. In this paper, current transport mechanisms were studied by current-voltage-temperature (I-V-T) testing from 100 K to 400K. For the samples deposited by a one-step sputtering process, the large value of ideality factor (n) and abnormal increase of barrier height with the temperature implies that the current transport mechanism does not follow the pure thermionic-emission theory, which was proven to be thermionic-field emission due to the highly doped Si film. By using a two-step sputtering process, the ideality factor and Au-Schottky barrier height at room temperature were about 1.5 and 0.7 eV, which was improved from one-step sputtering. Hydrogenation by electron cyclotron resonance (ECR) plasma can further improve the Schottky diode ideality factor and barrier height. Although a low-level Phosphors-doped Si target was used for poly-Si thin film deposition, a thermionic-field emission mechanism was still found by plotting the activation energy (E0) versus the testing temperature range. Capacitance-voltage (C-V) analysis revealed an unexpected carrier density of 1017 cm−3 level, which is 1000 times higher than the doping density level in the Si film. “Oxygen thermal donor” effect was assumed due to high oxygen level (1020 cm−3) detected by SIMS and processing at ∼ 600 °C. Increasing of the total carrier density due to the oxygen donor may cause the transport mechanism change from pure thermionic emission to thermionic-field emission. Reducing oxygen in the Si film by filtering the sputtering gas to 50 ppb oxygen level was proven to be effective. C-V results gave ∼1016 cm−3 level of carrier density after using oxygen filtering. P-N junction solar cells were made by B-ion implantation into n-type Si film and dopant activation at 700 °C. I-V-T study showed similar curves for P-N junction as for Schottky junction devices. This implies that the current transport was dominated by the Si films instead of the junctions for both Schottky and P-N junction devices.

The introduction of propylene carbonate (PC) into the poly (3-alkyl)thiophenes (P3AT) poly(octyl)thiophene (P3OT) and poly(hexyl)thiophene) (P3HT) is studied. In both cases, we observe a diminution of their melting temperature, which demonstrates a plasticizing effect. We also observe an increase of photovoltage and photocurrent in sandwich devices M//P3AT+PC//ITO-PET where M=Al, Mg and ITO-PET is Indium thin oxide coated on polyester. We attribute this effect to the introduction of oxygen from the PC. When mixed with an electron acceptor PCBM, the photocurrents only slightly increase and the photovoltages are similar. In this case, the presence of oxygen is detrimental to the system.