Se2 Thin Film Solar Cells Research Articles

Innovative industrial Cu(In,Ga)Se2 thin film solar cell with high characterization using nanoparticles structure

This paper presents new design of ZnO/CdS/CIGS/Mo nanocomposites thin film solar cell based on individual and multiple nanocomposites absorber layer. A theoretical analysis is presented for enhancing the efficiency and characterization of individual and multiple nanocomposites CdS/Cu (In, Ga) Se2 thin film solar cell. Moreover, this paper is achieving high efficiency with a thinner CIGS layer for reducing the direct materials usage and there by the materials costs by adding various metallic nanoparticles in CIGS absorber layer .

Innovative industrial Cu(In,Ga)Se2 thin film solar cell with high characterization using nanoparticles structure

This paper presents new design of ZnO/CdS/CIGS/Mo nanocomposites thin film solar cell based on individual and multiple nanocomposites absorber layer. A theoretical analysis is presented for enhancing the efficiency and characterization of individual and multiple nanocomposites CdS/Cu (In, Ga) Se2 thin film solar cell. Moreover, this paper is achieving high efficiency with a thinner CIGS layer for reducing the direct materials usage and there by the materials costs by adding various metallic nanoparticles in CIGS absorber layer .

Enhanced electrical conductivity of transparent electrode using metal microfiber networks for gridless thin-film solar cells

Improving the optical transmittance and electrical conductivity in transparent conductors (TC) has been a critical issue for decades due to their numerous applications. In this paper, we suggest an approach to produce extremely conductive TC material from electroplated Ni microfiber networks (NiMFs) in order to achieve highly efficient and aesthetically superior thin-film solar cells and modules. The high cross-sectional aspect ratio of NiMFs significantly enhanced their electrical conductivity and optical transmittance simultaneously. The TC structure employing NiMFs was a successful substitute for conventional patterned grids in Cu(In,Ga)Se2 thin-film solar cells because it reduced the series resistance, which is especially advantageous for large-area cells. The NiMF-induced transmittance loss was compensated for by the formation of a light diffusion layer on the NiMF. We propose that the excellent performance of NiMF TC materials enables the elimination or significant reduction of the grids in thin-film solar cells and modules.

Multifunctional metal oxide electrodes: Colour for thin film solar cells

Building integrated photovoltaics (BIPV) is an essential part to reduce the CO2 footprint of metropolitan areas. Currently, full integration of photovoltaic elements in a building is a very costly and complex undertaking, as it usually requires expensive custom modules. In order to increase the market share of BIPV in the residential mass market, a low-cost, flexible technical process to change the appearance of solar elements is required. Transparent conductive electrodes consisting of an oxide-metal-oxide (OMO) stack of thin layers have been optimized for application in thin film solar cells. Here the OMO stack is multifunctional: It provides the transparent front contact electrode and at the same time allows tuning of the module colour. This has several advantages compared to other colouring techniques, i.e. coloured glass or additional interlayers. The OMO colouring does not require an additional process step, and with sputtering an already existing deposition method is used. By varying the thickness of the oxide layers it is possible to change the reflected spectrum of the stack and with it the module colour. In this publication, we present how the optical model of the OMO stack, that is necessary for precise tuning of the colour, is first developed for OMO/glass samples and then report the changes necessary to adapt the OMOs for use on Cu(In,Ga)Se2 thin film solar cells.

Effects of Cu(In,Ga)3Se5 defect phase layer in Cu(In,Ga)Se2 thin film solar cells

Cu(In,Ga)3Se5 (135-CIGS) layers with various thicknesses were deposited on the surface of Cu(In,Ga)Se2 (112-CIGS) photon absorber in the fabrication of CIGS thin film solar cells. This significantly affects the shift of the optical band gap energy from 1.15 eV (112-CIGS) to 1.19 eV, with only 10 nm thick of 135-CIGS capping layer, leading to the increase in open-circuit voltage (Voc) of the solar cells. The optical transmission spectra show no sign of single 135-CIGS layer. The maximum Voc of 670 mV was obtained from 5 to 10 nm thick 135-CIGS capping layer on 112-CIGS compared to 646 mV of only 112-CIGS. The power conversion efficiencies of the devices covered with 135-CIGS with thickness of less than 80 nm are slightly lower than that of the uncovered 112-CIGS solar cells due to lower generated photocurrents. The solar cell parameters become dramatically deteriorate with thicker 135-CIGS capping layer. The XRD also shows the shift of the diffraction peak toward larger 2θ without peak broadening or splitting when the thickness of 135-CIGS is increased. The external quantum efficiency (EQE) measurements indicate the shift of absorption threshold towards shorter wavelength when the thickness of 135-CIGS is increased, which is consistent with the optical transmission measurements.

Enhancing photocurrent of Cu(In,Ga)Se2 solar cells with actively controlled Ga grading in the absorber layer

Highly efficient Cu(In,Ga)Se2 (CIGS) thin film solar cells are often fabricated with a double Ga grading along the thickness direction of the light absorber. In this work, through a progressive procedure of using time-dependent Ga and In deposition rates, it is manifested that how the detailed shape of the double Ga grading profile in terms of the depth of the V-shape, the width of the V-shape, and the spatial position of the minimum bandgap can be experimentally actively manipulated. Moreover, the effect of the aforementioned features of the Ga grading profile on the photo-generated current has been uncovered by the progressive improvement in the spectral response of the external quantum efficiency spectra. Within the effort of our optimization, a CIGS solar cell with a conversion efficiency of 20.3% is obtained, believed to be the best reported for CIGS solar cells without actively using alkali post deposition treatment technology. This work has provided a practical and operable route to actively control the Ga grading profile and turned the fabrication of high efficiency CIGS solar cell from an art to more a science.

Investigation of Mo:Na and Mo related back contacts for the application in Cu(In,Ga)Se2 thin film solar cells

In this study, sodium doped molybdenum (Mo:Na) and Mo thin films are deposited at different working pressures under the excitation of the radio frequency (RF) or direct current (DC) power supplies for application in Cu(In,Ga)Se2 (CIGS) thin film solar cells. The various material properties including dynamic deposition rate, electrical and optical properties, crystal structure and morphology are systematically investigated and compared for these RF and DC sputtered Mo:Na and Mo thin films. Mo and Mo:Na related back contacts, i.e. bottom Mo:Na layer prepared at a high working pressure and top Mo or Mo:Na thin film sputtered at a low working pressure are employed in CIGS thin film solar cells. CIGS thin film solar cells with Mo:Na (bottom, DC)/Mo:Na (top, DC) have a relatively high VOC, which is related to a relatively easy migration of Na passing through the DC Mo layers and entering into the CIGS thin film solar cells. A CIGS thin film solar cell of 14.0% has been achieved in this work.

The characteristics of Cu(In, Ga)Se2 thin-film solar cells by bandgap grading

We investigated the characteristics of Cu(In, Ga)Se2 solar cells with bandgap (Eg) grading. Two precursor types were employed: Mo/Cu0.75Ga0.25/In/Ga2Se3 (CIGSe-1) and Mo/Cu/In/Ga2Se3 (CIGSe-2). In CIGSe-1, the range of depths with a high Ga content is wider than that in CIGSe-2; thus, the region in which the main electron-trapping clusters and high-population deep donor defects can form is larger, and the defect density is higher. In the defect energy level range, various other defects and defect clusters exist with a defect density of 2.83 × 1015 cm−3 within the CIGS-1 absorber layer and 2.37 × 1015 cm−3 within the CIGS-2 absorber layer. The average efficiency values are 5.71% for CIGSe-1 and 6.82% for CIGSe-2. Additionally, the average VOC deficit (Eg/q − VOC) values are 0.758 V for CIGSe-1 and 0.731 V for CIGSe-2. As a result, in the 7 CIGSe-2 samples, the open-circuit voltage and efficiencies are improved. Thus, it is demonstrated that appropriate Eg grading in a CIGSe layer with a wider Eg on the back surface can result in improved performance.

Grain growth enhancing through preheating treatment of a sputtered stacked metallic precursor for Cu(In, Al)Se2 thin film solar cells application

The influence of preheating treatment of a sputtered stacked metallic precursor on structural property of the CuInAl precursor and detailed structural, morphological and optical analyses as well as in the finally obtained Cu(In, Al)Se2 (CIAS) thin film solar cell device characterization are investigated systematically. These results indicate that this preheating process exhibits a strong beneficial impact on crystal growth and eventually produces a substantial improvement in photovoltaic properties. However, further increase of the preheating temperature, despite enhancing grain growth, clustering of grains loosely distribute on the surface of the CIAS thin film, forming a rather rough morphology. Thus, an accurate control of the preheating temperature during grain growth process may be necessary. Here, when optimizing the preheating temperature to 300 °C, the largest grain size and the best photovoltaic performance achieved. The findings provide an important insight into the understanding of fundamental research of current chalcopyrite solar cell application.

Performance of Cu(In, Ga)Se₂ Solar Cells on Zinc Sulfide Buffer Layers for Various Power Values of an Intense Pulsed Light System.

The effect of using an Intense Pulse Light system has been studied on zinc sulfide thin films and Cu(In, Ga)Se₂ solar cells. The deposition of thin films on the zinc sulfide buffer layer is carried out on the glass and Cu(In, Ga)Se₂ using the chemical bath deposition process. These zinc sulfide thin films were then subjected to treatment at different irradiation light intensities from 500 W to 2000 W, and then the effects on the layer were compared to a thermal annealed layer. The morphology and optical transmittance of the zinc sulfide layer were analyzed by field emission scanning electron microscopy and ultraviolet-visible spectrophotometry, respectively. This methodology was also applied to fabricate and investigate the efficiency, short-circuit current density, and external quantum efficiencies of the solar cells. This analysis shows that the treatments significantly change the properties of the zinc sulfide buffer layer and performance of the Cu(In, Ga)Se₂ thin film solar cells.

Polarization photo absorption spectroscopy of ZnO/CdS/Cu(In, Ga)Se2 thin film solar cells

The photosensitivity of polycrystalline-film Cu(ln,Ga)Se2/CdS/ZnO solar cells with different thickness of CdS and ZnO films have been studied. These structures exhibit a conversion efficiency 11-12% in the spectral region from 1.2 to 2.4 eV at T= 300 K. Polarization photosensitivity was observed for oblique incidence of linearly polarized light on the ZnO surface of these structures. The induced photopleochroism and an increase of the photocurrents as a result of a decrease of reflection losses were found. The induced photopleochroism 82 coefficient P1 increases with the angle of incidence E> as P1- and its value isfound to be 10-17% at E>= 75e°. The results of these polarization investigations demonstrate the sensitivity of the photoelectric processes to the optical quality of the ZnO films. Such polycrystalline-film solar cells can be employed as polarization-photosensitive devices.

Photovoltaics literature survey (no. 149)

Photovoltaics literature survey (no. 149)

Enhanced spectral response of CIGS solar cells with anti-reflective subwavelength structures and quantum dots

A cover glass integrated with subwavelength structures (SWSs) and quantum dots (QDs) was realized to enhance the spectral response of Cu(In1-xGax)Se2 (CIGS) thin film solar cells. The nanoscale SWSs was produced on the front and backside of cover glass using the self-masked etching method. The fabricated SWSs-integrated glass (SIG) exhibited superior anti-reflective properties over a broad wavelength range and a broad range of incident angle. The average transmittance of the single and double-sided SIG was increased from 92.4% to 95.2% and 97.8% in the wavelength range between 300 and 1200 nm, as compared to that of a flat surface glass. QDs were formed between the fabricated SIG and ZnO layer to act as a luminescent down-shifting (LDS) layer. A large amount of light can pass through the SIG, enhancing the efficiency of the LDS by improving light absorption and lowering reflection. After successful integration of the SIG with QDs (QD/SIG) on top of the CIGS devices, photovoltaic performance was significantly improved. The power conversion efficiency of the CIGS devices integrated with QD/double-sided SIG was improved by 7.41%, compared with that of a reference device (without QD/cover glass). The efficiency improvement is attributed to the enhanced solar energy harvesting by the efficient LDS and the minimized surface reflection loss.

Effective ink-jet printing of aqueous ink for Cu (In, Ga) Se2 thin film absorber for solar cell application

Chalcopyrite Cu (In, Ga) Se2 (CIGSe2) thin film solar cells have emerged as a popular absorber material among thin film technologies, leading with photoconversion efficiency more than 22% on lab scale already being reported. Solution processed absorber ink using non-vacuum route found to be cost effective and for scalable approach of CIGSe2 thin film solar cells. In this context, Inkjet printing emerges as a feasible technique for manufacturing CIGSe2 thin film solar cells. Here, inkjet printing of aqueous precursor ink to successfully make high-quality CIGSe2 absorber layer with controlled thickness and morphology is being presented. Precursor ink in aqueous medium and ink jetting parameters were optimized to obtain stable drop formation, essential for high-quality precursor film. The parameters that are found to strongly influence the formation of quality precursor CIG film were drop spacing and pretreatment temperature, discussed in detail. The effects of ink properties and printing parameters were investigated through rheological studies and optical microscopy; results suggested that uniform coverage of precursor CIG film can be achieved using a drop spacing of 175 µm and pretreatment temperature of 150 °C. A single phase highly crystalline chalcopyrite CIGSe2 thin film with dense morphology was obtained using atmospheric pressure selenization process. Semiconducting properties of film was studied by Mott-Schottky analysis. The photovoltaic performance of CIGSe2 film solar cell device fabricated using non-vacuum inkjet route demonstrated 4.0% photoconversion efficiency on active device area of 4 × 4 mm2.

Determination of the lateral collection length of charge carriers for silver-nanowire-electrode-based Cu(In,Ga)Se2 thin-film solar cells

Silver nanowire (AgNW) electrodes have been employed in solar cells as transparent conducting electrodes (TCEs). When a AgNW electrode is used as a network-type TCE in solar cells, photogenerated charge carriers must laterally travel to reach AgNW networks. If the empty space of the network is larger than the lateral collection length of the charge carriers (Llc), a significant fraction of the charge carriers will be lost. Therefore, determination of Llc is essential for choosing and/or designing a suitable network for solar cells. Here, we develop a method to relate the lateral photocurrent measured from a specially designed pattern to the Llc value. We apply this method to Cu(In,Ga)Se2 thin-film solar cells with AgNW TCEs. The Llc value was determined to be ≈26 μm in the CdS/CIGS/Mo structure under 1-sun illumination. The measured lateral collection length is much larger than the normal spacing between AgNWs, indicating a high lateral collection efficiency in AgNW TCE-based CIGS thin-film solar cells.

Effects of substrate orientation and solution movement in chemical bath deposition on Zn(O,S) buffer layer and Cu(In,Ga)Se2 thin film solar cells

With a colloid aggregation process, chemical bath deposited (CBD) Zn(O,S) thin films always consist of many particles or clusters on the surface and their removal is a long-standing problem. In this work, by varying the substrate orientations and solution movements, their effects on the quality of the Zn(O,S) layers, the formed junctions, and the performance of the Zn(O,S)-Cu(In,Ga)Se2 (CIGS) solar cells have been systematically investigated. Unlike CBD-CdS growth for which stirring or rocking the solution is a common and useful practice for improved quality, surprisingly, for CBD-Zn(O,S) growth, solution movement plays a primary role and substrate orientation plays a secondary role to influence the film quality and the device performance. Equally surprising, the above effects strongly depend on the recipes and chemicals used for the CBD process. It has been identified that, independent of recipes, depositing Zn(O,S) films with the substrate inclined in a static solution can minimize the formation of particles/clusters, generate homogeneous and high quality buffer layers on CIGS with the best device performance. Disturbing the CBD solution would in general introduce large particles/clusters to adsorb on the Zn(O,S) films, leading to degraded junction quality, strong light soaking effect, and poor device performance.

A study of ZnO:Al thin films reactively sputtered under the control of target voltage for application in Cu(In,Ga)Se2 thin film solar cells

In this study, aluminum doped zinc oxide (ZnO:Al) thin films were prepared by reactive magnetron sputtering from Zn:Al metallic targets with different Al contents (0.5 wt%, 1.5 wt%, 2.0 wt% and 2.5 wt%). The reactive sputtering process was monitored and controlled with a gas loop controller. The crystal structures, morphologies, chemical compositions, optical and electrical properties of the reactively sputtered ZnO:Al thin films were systematically investigated. In addition, the reactively sputtered ZnO:Al thin films were applied as window layers in Cu(In,Ga)Se2 (CIGS) thin film solar cells. The corresponding performances of solar cells were also studied. High efficiency of 16.2% was achieved for CIGS thin film solar cells with reactively sputtered ZnO:Al window layers in this study, which was slightly lower than 17% of reference cell with radio frequency (RF) non-reactively sputtered ZnO:Al window layer.

Alkali Postdeposition Treatment-Induced Changes of the Chemical and Electronic Structure of Cu(In,Ga)Se2 Thin-Film Solar Cell Absorbers: A First-Principle Perspective.

The effects of alkali postdeposition treatment (PDT) on the valence band structure of Cu(In,Ga)Se2 (CIGSe) thin-film solar cell absorbers are addressed from a first-principles perspective. In detail, experimentally derived hard X-ray photoelectron spectroscopy (HAXPES) data [HandickE.; ACS Appl. Mater. Interfaces2015, 7, 27414−2742026633568] of the valence band structure of alkali-free and NaF/KF-PDT CIGSe are directly compared and fit by calculated density of states (DOS) of CuInSe2, its Cu-deficient counterpart CuIn5Se8, and different potentially formed secondary phases, such as KInSe2, InSe, and In2Se3. The DOSs are based on first-principles electronic structure calculations and weighted according to element-, symmetry-, and energy-dependent photoionization cross sections for the comparison to experimental data. The HAXPES spectra were recorded using photon energies ranging from 2 to 8 keV, allowing extraction of information from different sample depths. The analysis of the alkali-free CIGSe valence band structure reveals that it can best be described by a mixture of the DOS of CuInSe2 and CuIn5Se8, resulting in a stoichiometry slightly more Cu-rich than that of CuIn3Se5. The NaF/KF-PDT-induced changes in the HAXPES spectra for different alkali exposures are best reproduced by additional contributions from KInSe2, with some indications that the formation of a pronounced K–In–Se-type surface species might crucially depend on the amount of K available during PDT.

Improved efficiency of Cu(In,Ga)Se2 thinfilm solar cells using a buffer layer alternative to CdS

The chalcopyrite semiconductor CuInSe2 and its constitutes Ga and/or S [Cu (InGa)Se2 or Cu (InGa)(Se,S)2], commonly referred as CIGS have been leading thinfilms for incorporation in high-efficiency photovoltaics. In conventional ZnO-N/i-ZnO/CdS/CIGS solar cells, the traditional CdS buffer is nearly optimum for the commonly used 1.15 eV (CIGS) but less optimal for higher Ga. To overcome this limitation, Cd1-yZnyS is proposed as an alternative buffer layer to replace the standard CdS in CIGS thinfilm solar cells containing an ordered vacancy compound (OVC) layer. Next, the dependence of solar cells performance on the change of Ga and Zn concentrations in absorber and buffer layers, respectively, was investigated using the AMPS-1D software. The results are potential improvement in CIGS efficiency that was obtained with replacement of CdS buffer material by its alternative in one hand, another hand by formation of OVC layer. Lastly, the optimum values of Ga and Zn concentrations were found at 0.7 and 0.6, respectively, leading to a high conversion efficiency of around 23.71%.

Low‐Temperature Growth of Submicron Cu(In, Ga)Se2 Solar Cells Based on Molybdenum Oxide Back Interface Layer

Cu(In,Ga)Se2 (CIGS) thin film solar cells are proven to be highly efficiency. However, lowering the substrate temperature and reducing absorber layer thickness can lead to severe light and electric losses. In this work, the authors employ molybdenum oxide acting as back interface layer in order to decrease the recombination at the rear interface in low‐temperature growth of submicron CIGS solar cells. X‐ray photoelectron spectroscopy (XPS) results show that the compositions of molybdenum oxide films are mainly MoOx(2 < x < 3) under the influence of metal molybdenum substrate and CIGS absorber. Meanwhile, the authors study the properties of CIGS devices with different MoOx thicknesses. They find that MoOx with appropriate thickness can facilitate the crystallization of CIGS absorber layer and restrain the recombination in the CIGS bulk as well as at the back interface. Finally a CIGS solar cell with active area efficiency of 11.8% is fabricated by low‐temperature processes below 450 °C when the thicknesses of absorber layer and molybdenum oxide are 0.92 and 10 nm, respectively. Compared with the reference device, absolute increase about 40 mV and 13% for Voc and FF are achieved.