In this paper the effect of Si1-xGex absorber layer thickness on thin film a-Si:H/crystalline-Si1-xGex/c-Si heterojunction solar cells (HIT cells) is studied by simulation and experiment. Cells with 1, 2 and 4 μm-thick epitaxial cap layers of p-type Si0.59Ge0.41 on top of 5 μm Si1-xGex graded buffer layers are fabricated and compared to study the effect of the absorber layer thickness. The results show no change in Voc (0.41V) and that Jsc increases from 17.2 to 18.1 mA/cm2 when the Si0.59Ge0.41 absorber layer thickness is increased from 1 to 4 μm. The effect of thickness on Jsc is also observed for 2 and 4 μm-thick Si and Si0.75Ge0.25 absorber layers. Experiments and simulations show that larger Ge fractions result in a higher magnitude and smaller thickness dependence of Jsc, due to the larger absorption coefficient that increases optical carrier generation in the near surface region for larger Ge contents.

Pyrite phase of FeS2 has attracted substantial attention in the field of thin film solar technology because of its high optical absorption coefficient (~5 x 105 cm-1 at hν > 1.3eV) and the band gap of 0.95 eV. In this research, we have grown highly pure iron pyrite films using a low temperature atmospheric pressure chemical vapor deposition technique. The synthesis temperature is in the range of 375-400°C and Di-tert-butyl disulfide (TBDS) is used as the sulfur precursor. TBDS is a safe and low cost sulfur source unlike H2S, which is highly toxic and requires extreme care in handling. The films obtained were uniform and free from common impurity phases such as troilite and marcasite. The FeS2 films grown earlier with CVD synthesis and sulfurized using H2S had pinholes and contained secondary phases like marcasite and troilite. The FeS2 pyrite phase was confirmed using various characterization techniques that included SEM, EDS, XRD and XPS.

The solar cells employed in low to medium (50 to 200 suns) concentration photovoltaic (CPV) are usually mono-crystalline silicon. Laser Groove Buried Contacts (LGBC) are preferred to screen printing in these cells due to the high currents generated in the system. In this paper, we report on the use of Coherence Correlation Interferometry (CCI) to accurately measure the width and depth of the laser-ablated grooves. In addition, the technique is also used to measure the surface roughness at the bottom of the trenches, since this can determine the success of the subsequent plating process, and at the top surface to optimize the debris control and obtain clean surfaces and well-shaped groove edges. The laser ablation process was also optimized to obtain the groove aspect ratio and surface quality required. Process parameters to be controlled include laser power, pulse energy, stage speed and focal length. The CCI technique is capable of providing all the groove and surface metrology required for this process optimization.

A low-resistance back contact for n-CdS/p-CdTe solar cells has been developed, which utilizes a thermally evaporated MoOx thin film as the buffer layer between the p-CdTe and the back electrode. The low-resistance behavior of back contact is attributed to the high work function of MoOx, which reportedly is as high as 6.8 eV, and thus adequately matches that of p-CdTe. With MoOx as the buffer, a variety of common metals, even those with a low work function such as Al, have been found to be useful as the electrode in forming the back contact. Other advantages of the MoOx buffer include dry application by vacuum deposition, and thus it is particularly suitable for the fabrication of ultra-thin CdTe solar cells without introducing additional shorting defects. Surface cleaning of CdTe films prior to MoOx deposition has also been studied. The cell stability has been evaluated through thermal annealing tests. Thermal degradation has been explained in terms of oxidation of the metal electrodes. CdTe cells with high efficiency and good stability have been demonstrated with MoOx as the back contact buffer and Ni as the electrode.

Thin films of antimony sulfide (Sb2S3) were prepared with different silver-ion content in a chemical deposition bath, and silver antimony sulfide (AgSbS2) was produced through the addition of higher concentrations of silver-ions in the bath. The chemical deposition solution mixture contained antimony trichloride (SbCl3) and sodium thiosulfate (Na2S2O3). For molar ratio, AgNO3:SbCl3, 0.002 – 0.02, XRD patterns of the Sb2S3-Ag films heated at 280 ºC match that of the mineral stibnite (Sb2S3). The optical band gap (Eg) of these films is in the 1.93-1.80 eV range. At higher molar concentrations of Ag, lower is the Eg of the films. Electrical conductivity under illumination (σph) is 7.4x10-5 Ω-1cm-1 for a film with Ag:Sb 0.002 in the bath, which is about three orders of magnitude higher than that of a film prepared without Ag. At Ag:Sb 0.2, the XRD pattern of the heated film shows the presence of Ag3SbS3 and AgSbS2. Single-phase AgSbS2 (cubic miargyrite, a = 0.5652 nm) film is formed for Ag:Sb 0.4 and the film heated at 260 oC. The Eg of the film is 1.75 eV for the Sb2S3/Ag-Sb-S film and 1.68 eV for AgSbS2. Solar cell structures of TCO(SnO2:F)/CdS(200 nm)/Sb2S3(150 nm)/graphite, as well as with Sb2S3-Ag absorbers were developed through sequential chemical deposition. The cells with the colloidal graphite paint on the absorber were heated at 260 ºC for 15 min each. The Voc of the cells are 620-635 mV, with the cell using Sb2S3-Ag (0.004) film showing a Jsc of 2.00 mA/cm2, which is higher than the 1.69 mA/cm2 observed in cells with Sb2S3 absorber. In cells using AgSbS2 absorber, Voc is 490 mV, and Jsc is very low, 0.12 mA/cm2. The present work offers a wider range of absorber materials for thin film and hybrid solar cells.

While the global market for photovoltaic (PV) modules continues to grow 30% - 40% annually, manufacturers are looking at advanced technologies and cell concepts in order to improve the cost performance and reliability. One of the challenges faced by the silicon (Si) PV manufacturers is the lack of efficient metal screen-printing technologies. While screen-printing is a long-established technology, THE traditional silver-based pastes have technical limits in terms of paste composition, drying and thermal-firing conditions, line-width, aspect ratio, contact resistance, etc. Such limits keep the industrial cell structure from being close to an ideal PV cell architecture. In an effort to develop alternate printable pastes electrically, electrically conductive adhesives are considered in this study to provide fine-line contacts and low thermal budget so that performance-driven solar cell designs can be reliably implemented in manufacturing. Mechanical properties of solar cell printed by conductive adhesives are experimentally investigated in this work and confirmed with the simulation results.

Aluminum-doped zinc oxide (ZnOx:Al) films have been deposited on a moving glass substrate by a high throughput metalorganic chemical vapor deposition process at atmospheric pressure. Thin (< 250 nm) ZnOx:Al films have a poor crystalline quality, due to a small grain size and the presence of different crystallographic orientations. The crystalline quality improves with increasing film thickness (from 50 nm to 1000 nm), resulting in a lower value of resistivity (from 100 Ohm cm to 1·10-3 Ohm cm, respectively). We have investigated the variation in the films’ conductivity and transparency induced by a post-deposition exposure to a He/H2 atmospheric plasma. The resistivity of thin (< 250 nm) films is found to decreased sharply from 100 Ohm cm to about 4·10-3 Ohm cm by a short (∼ seconds) plasma exposure, while the resistivity of thicker films remains unaffected.

CdTe and CdS are emerging as the most promising materials for thin film photovoltaics in the quest of the achievement of grid parity. The major challenge for the advancement of grid parity is the achievement of high quality at the same time as low fabrication cost. The present paper reports the results of the new deposition technique, Pulsed Plasma Deposition (PPD), for the growth of the CdTe layers on CdS/ZnO/quartz and quartz substrates. The PPD method allows to deposit at low temperature. The optical band gap of deposited layers is 1.50 eV, in perfect accord with the value reported in the literature for the crystalline cubic phase of the CdTe.

The films are highly crystalline with a predominant cubic phase, a random orientation of the grains of the film and have an extremely low surface roughness of 4.6±0.7 nm r.m.s.. The low roughness, compared to traditional thermal deposition methods (close space sublimation and vapour transport) permits the reduction of the active absorber and n-type semiconductor layers resulting in a dramatic reduction of material usage and the relative deposition issues like safety, deposition rate and ultimately cost

We report CdTe/CdS solar cell with CdTe layer grown by sputtering method. A controlled etch and anneal process on the sputter-grown CdTe films was performed to increase the average grain size of the film. The process involved dipping the CdTe films in a saturated solution of cadmium chloride (CdCl2) in methanol (2.08 gram in 100 ml) followed by a 30 minute annealing at 400 °C. We performed various experiments on this process by varying the dipping times, drying process and annealing times and analyzed the resultant films using Scanning Electron Microscopy (SEM). We could see a clear increase in grain size from 200 nm to 5 μm after CdCl2 treatment. The process also increased the overall roughness of the sample so that more light is absorbed than reflected. We prepared solar cells using CdTe as p-type layer and CdS as n-type layer. The efficiency of the cell improved from 1.1% to 4.2% after air annealing. The effect of air-annealing is studied by means of quantum efficiency measurement.

A water vapor barrier layer is presented that is deposited entirely at temperatures below ∼100oC. Our method, using hot wire chemical vapor deposition (HWCVD), is effective in reducing the issue of pinholes in single layers of silicon nitride (SiNx) made at such low substrate temperatures. We succeeded in depositing an all hot-wire simple three-layer structure consisting of two low-temperature SiNx layers with a polymer layer in between, exhibiting a water vapor transmission rate (WVTR) as low as 5*10-6 g/m2/day, determined at a temperature of 60°C and a relative humidity of 90%. This WVTR is low enough for organic and polymer devices. In a second experiment the robustness of the barrier layer is shown with respect to environmental dust.

A primary challenge to the industrial uptake of dye-sensitized solar cells (DSC) is the ability to improve manufacturing efficiency. New thinking is required in terms of lowering cost, improving the process steps and increasing throughput. The typical manufacture of a DSC contains a number of long process steps; the sintering and dyeing of the TiO2 are prime examples. The current solution is to batch process on rigid substrates or use long energy intensive convection ovens for flexible metal substrates. Here we present a method for reducing some of the bottlenecks in the manufacturing process using near infra red radiation to speed up the thermal treatment of TiO2 and silver inks reducing their processing times to 12 and 2 seconds from normal process times of 30 and 10 minutes respectively.

Although pyrite (FeS2) is abundant, getting a single-phase pyrite thin film is difficult due to the coexistence of various phases of iron and sulfur in nature. We propose an ink-based process for attaining the pyrite phase of iron sulfide. This work involves degassing Iron (II) chloride in an octadecylamine solution and later reflux with addition of sulfur in diphenyl ether at 200°C. The process yielded phase-pure single crystalline pyrite nanocrystals which were later cleaned and dispersed in chloroform for uniform suspension. Thus obtained nanocrystals were deposited as thin films using drop casting and spin coating. Solar cells were fabricated using CdS as an n-type window layer in a superstrate configuration. When tested, the superstrate type FeS2 nanoparticle cell showed 0.03% with high Voc of 565 mV.

In the past two decades, the growing global demand for solar energy has spurred scientific interest in alternative technologies to conventional silicon. In particular, CuIn1-xGaxSe2 (CIGS) has emerged as a competitor. We have developed a scalable deposition technique using RF magnetron sputtering of quaternary CIGS. Notably, the resulting films do not require postselenization, reducing processing time and cost. We have fabricated devices above 10% efficiency using this approach, showing its promise as a production method for highperformance CIGS photovoltaics. However, the morphology of the sputtered CIGS layer is markedly different from conventional evaporated films; grain sizes vary through the thickness of the film, with numerous small grains dominating at the Mo/CIGS interface that then either terminate or grow in an inverted-pyramid fashion to form large, columnar grains at the CIGS/CdS interface.

To better understand the origin of this morphology, we have studied the growth behavior of the CIGS layer using a combination of atomic force microscopy and electron microscopy to observe initial nucleation and grain growth behavior of quaternary-sputtered CIGS. We also discuss the effects of interfacial layers at the Mo/CIGS interface, demonstrating a novel wetting layer that conformally coats the Mo surface.

In the present work we report the synthesis of Cu2ZnSnS4 (CZTS) films by pulsed laser deposition (PLD) and the effect of sulfur annealing on structure, composition, morphological and optical characterization of CZTS thin films. Raman spectra of the films exhibited the characteristics peaks of Kesterite structure. However, annealing caused to transfer the films from amorphous state into crystalline state. Scanning electron microscope (SEM) images revealed that as-deposited film exhibited a crack free, smooth, densely packed and homogeneous surface which was changed to rigid granular appearance after annealing. Energy dispersive X-ray spectroscopy (EDS) determined the compositions of the CZTS thin films which was near stoichiometry for the annealed samples. Ultraviolet–visible (UV–Vis) spectra showed the band gap of as-deposited film was 1.60 eV which was decreased to 1.40 eV after annealing.

A crucial step in Dye Solar Cell (DSC) fabrication is the sintering of the TiO2 layer which needs to guarantee good electromechanical bonding between nanoparticles whilst maintaining sufficiently large porosity to yield performing devices. The standard procedure for TiO2 sintering requires firing in an oven at ∼ 500°C. An alternative procedure consists in utilizing laser scanning processing which has the advantageous potential of being noncontact, local, low cost, rapid, selective, automated and scalable. We analyzed and optimised a laser process for the sintering of the TiO2 layers in dye solar cells analyzing temperature profiles, throughput and the embodied energy. The development of electronic and photovoltaic devices on plastic substrates is of considerable interest due to the advantages they bring in terms of flexibility and easy processing for lightweight, low-cost large-area applications. An alternative sintering procedure compatible with flexible substrates and large area processing consists in utilizing a UV lamp. We subjected TiO2 pastes deposited on conductive transparent substrates to UV irradiation. Fully plastic devices fabricated through this method showed efficiencies of 4%.

CuInS2 (CIS) films were prepared by chemical spray pyrolysis (CSP) method in air using CuCl2, InCl3 and SC(NH2)2 as precursor materials. The effect of the absorber growth temperature in the interval of 240-350 °C and precursors’ molar ratio in the spray solution on the CIS film properties and ZnO/In2S3/CIS-type CSP-deposited thin film solar cell output characteristics has been studied. CIS films were characterized by XRD and EDX, solar cells were characterized by IV curves in dark and under illumination, and junction barrier height (Φb). The highest Φb of 1170 meV and open circuit voltage (Voc) of 560 mV were recorded for the cell with CIS absorber grown at 250 °C. Increasing the CIS deposition temperature decreases Φb and Voc, makes a component of solar cell photosensitive and increases current density. The precursors’ molar ratio in spray solution becomes relevant at CIS growth temperatures higher than 300 °C as deposition of thiourea-rich solutions suppresses oxide formation in CIS layer and contributes to higher open circuit voltage.

It has been demonstrated in literature that chemical liquid deposition (CLD) processes such as dip coating, spray coating, roll coating, spin coating, curtain coating, meniscus coating etc. can be successfully used to deposit anti-reflective coatings on glass substrates. In comparison to physical vapor deposition (PVD), a CLD process generally is cost efficient because of lower capital requirements to set up coating manufacturing lines. Within the realm of CLD processes only some application techniques are suitable for high speed continuous manufacturing processes to deposit coatings on large area glass substrates. Significant differences in transfer efficiencies of these high speed application processes are readily apparent when material utilization per unit area of glass are compared. Roll coat process among all the high speed CLD processes stands out for its high material transfer efficiency due to direct contact printing on flat glass substrates. Honeywell Electronic Materials expanded its line of SOLARC® anti-reflective coating materials to include a new coating formulation SOLARC® RPV, which is customized for roll coating application. This paper highlights the advantages of using SOLARC® RPV in roll coat process and the performance attributes of SOLARC® anti-reflective coatings. Durability characteristics of these anti-reflective coatings in accelerated aging tests designed to simulate harsh field conditions will also be discussed.

We present a numerical study on effect of temperature on the performance of a waveguide luminescent solar concentrator (LSC). The purpose is to determine how changes in temperature of the ambient environment of an LSC affect device performance. The thermo-optical coefficient of the polymer waveguide is modeled using the well known Prod’homme formulation and applied in a forward Monte Carlo ray-tracing simulation. We show that the number of collected photons decreases almost linearly as the ambient temperature increases from -50 ºC to +50ºC. This behavior is associated with several competing loss mechanisms in the waveguide. For example, increases in optical confinement due to increased refractive index at low temperature are opposed by increases in cone loss (escape loss) of photons. Other competing mechanisms that exhibit temperature dependence are explained in terms of a detailed balance treatment of the LSC as a function of temperature.

To understand paths towards higher efficiency (η) for copper-indium-gallium-(sulfur)-selenide [CIG(S)Se] solar cells, we investigated a variety of absorber composition grading schemes for various back-side gallium (Ga), front-side sulfur (S), and double-graded Ga composition depth profiles in TCAD 1D/2D simulations. We fitted experimental results of a Back-Side Graded (BSG) solar cell with our TCAD models, prior to investigating other grading and interface schemes. The BSG solar cell was fabricated on a High Productivity Combinatorial (HPC™) platform based on sputtering Cu(In,Ga) followed by selenization. Our TCAD simulation methodology for optimizing CIG(S)Se solar cells started with a sensitivity analysis using 1D Solar-cell CAPacitance Simulator (SCAPS) [1] by selecting a typical range of key model parameters and analyzing the impact on η. We then used a 2D commercially-available Sentaurus simulation tool [2] to incorporate wavelength-dependent optical characteristics. As a result, we provide insight in the impact of grading schemes on efficiency for a fixed ‘material quality’ equal to an in-house BSG solar cell. We also quantify the effects of interface layers like MoSe2 at the Mo/CIG(S)Se interface, and an inverted surface layer at the CIG(S)Se/CdS interface.

In this study indium tin oxide (ITO) thin films have been deposited by RF sputtering technique on quartz substrate. In all cases, the substrate was heated during deposition. Thin film deposited under various process conditions, shows characteristic XRD reflection corresponding to the (222) crystal orientation. Transmittance of the film has been measured for the wavelength range from 190 to 3300 nm. Average transmittance of 84.4%, 90.2% and 85.3% for wavelengths up to 800 nm, 2500 nm and 3300 nm respectively has been obtained. The resistivity in this case is found to be as low as ∼10 × 10-4 Ω-cm. Our study is focused on controlling the resistivity of the deposited film, without compromising transmittance in the near infra red (NIR) region of the spectrum. Substrate heating during deposition is found to result in films with grains which are oriented in (222) direction predominantly. Moreover, the average grain size is increased with subsequent annealing. It has been observed that though the transmittance for the samples doesn’t vary substantially upon annealing the resistivity decreases by several factors.