Efficient CuInSe 2 Solar Cells Fabricated by a Novel Ink Coating Approach

A novel technique is developed for the deposition of CuInSe 2 (CIS) thin films for solar cell applications. The technique uses an ink formulation that contains Cu-In metallic pigments. A precursor layer is first formed coating this ink onto the selected substrate. The precursor film is then reacted with Se to form the CIS compound. Solar cells were fabricated on CIS absorber layers prepared by this low cost ink coating approach and devices with a conversion efficiency of over 9.0% were demonstrated. © 1998 The Electrochemical Society. S1099-0062(98)08-063-8. All rights reserved. Manuscript submitted August 14, 1998; revised manuscript received September 9, 1998. Available electronically October 1, 1998. Group I-III-VI materials are considered to be highly promising as absorber layers in high-efficiency thin film solar cell structures. In fact, the highest efficiency thin film device to date was produced on a Cu(In,Ga)Se 2 (CIGS) absorber film grown by a vacuum evaporation technique. The demonstrated conversion efficiency of 17.7% confirmed the capability of this material to yield highly efficient active devices when employed in thin film solar cell structures. High-efficiency solar cells have commonly been fabricated on CuInSe 2 (CIS) or CIGS absorbers deposited by costly vacuum deposition techniques such as coevaporation 1 and two-stage processes utilizing evaporation or sputtering. 2 There is presently great interest in the development of new lower cost processing methods for the growth of high quality CIS-type absorbers for thin film solar cell applications. Slurry or ink deposition by large area nonvacuum coating methods such as screen printing, spraying, curtain coating, roll coating, or doctor blading are attractive low-cost approaches for the growth of thin film solar cell absorbers, provided that the precursor layers obtained by these deposition techniques can be converted into high quality semiconductor films that are required for solar cell fabrication. There have been several attempts to deposit CIS absorbers using the screen printing technique. For example, Arita et al. described a method that involved (i) mixing pure Cu, In, and Se powders in the compositional ratio of 1:1:2, (ii) milling these powders in a ball mill and forming a screen printable paste, (iii) screen printing the paste on a substrate, and (iv) sintering this precursor film to form the compound layer. As can be seen from the review of previous work, the nature of the ingredients in the formulation of a paste or an ink is very important for the formation of a precursor layer which can later be converted into a high quality CIS-type compound film with properties that are desirable for solar cell applications. In this article we report a low-cost ink coating technique that was successfully employed for the deposition of CIS absorbers that could be used for the fabrication of over 9% efficient thin film solar cells. Experimental The general steps of the low-cost process used in this work for the growth of thin film CIS absorbers are schematically shown in The source of Cu and In in this work was a Cu-In alloy powder with a preselected and fixed Cu/In stoichiometric ratio. The Cu-In alloy powder was obtained by the melt atomization technique. To prepare the powder, 99.99% pure Cu and 99.99% pure In were melted under a hydrogen curtain at above 900°C. The Cu/In ratio of the melt corresponded to the targeted value range of 0.87-0.9. The melted alloy was transformed into powder in a gas atomizer employing Ar as the quenching gas. Quenched powder was collected at the bottom of the reactor and sieved to separate the particles that were smaller than 20 µm in size which were used in this work as the pigment. About 10 g of the Cu-In pigment was mixed with 23 g of water. A small amount (about 1.5 wt %) of a wetting agent and dispersant were added to this aqueous formulation. The mixture was milled in a ball mill for 42 h. The resulting metallic ink was water-thin. Particle size analysis was done on a sample of this ink using

Optimisation of pH of cadmium chloride post-growth-treatment in processing CDS/CDTE based thin film solar cells

The role of Chlorine-based activation in the production of high quality CdS/CdTe photovoltaic have been well discussed and explored with an overlook of the effect of Cadmium chloride (CdCl2) post-growth treatment acidity on the property of the fabricated devices. This work focuses on the optimisation of CdCl2 post-growth treatment pH as it affects both the material and fabricated device properties of all-electrodeposited multilayer glass/FTO/n-CdS/n-CdTe/p-CdTe configuration. CdCl2 treatments with acidity ranging from pH1 to pH4 were explored. The properties of the ensued CdTe layer were explored using optical, morphological, compositional structural and electrical property analysis, while, the effect on fabricated multilayer glass/FTO/n-CdS/n-CdTe/p-CdTe configuration were also explored using both I-V and C-V measurements. Highest improvements in the optical, morphological, compositional and structural were observed at pH2 CdCl2 post-growth treatment with an improvement in absorption edge, grain size, crystallinity and crystallite size. Conductivity type conversions from n-CdTe to p-CdTe, increase in pin-hole density and collapse of the absorption edge were observed after pH1 CdCl2 treatment. The highest fabricated solar cell efficiency of 13% was achieved using pH2 CdCl2 treatment as compared to other pH values explored

Optimisation of CdTe electrodeposition voltage for development of CdS/CdTe solar cells

Cadmium telluride (CdTe) thin films have been deposited on glass/conducting glass (FTO) substrates using low-cost two electrode system and aqueous electrodeposition method. The glass/FTO substrates were used to grow the CdTe layers at different deposition voltages. The structural, electrical, optical and morphological properties of the resulting films have been characterized using X-ray diffraction (XRD), Photoelectrochemical (PEC) cell measurements, optical absorption spectroscopy and Scanning Electron Microscopy (SEM). The XRD results indicate that at voltages less than or higher than 1.576 V, crystallinity is poor due to presence of two phases. When CdTe is grown at 1.576 V, the composition is stoichiometric, and the (111) peak has the highest intensity in the XRD diffractogram indicating a high degree of crystallinity. SEM studies showed that all layers had pin-holes and gaps between the grains. These openings seem to be more common in the samples grown at voltages away from the stoichiometric voltage (1.576 V). The linear I–V curves of glass/FTO/CdS/CdTe/Au structures fabricated using stoichiometric CdTe showed efficiency of 10.1 % under AM 1.5 illuminatio

Effects of Cd1-xZnxS alloy composition and post-deposition air anneal on ultra-thin CdTe solar cells produced by MOCVD

Ultra-thin CdTe:As/Cd1-xZnxS photovoltaic solar cells with an absorber thickness of 0.5 μm were deposited by metal-organic chemical vapour deposition on indium tin oxide coated boro-aluminosilicate substrates. The Zn precursor concentration was varied to compensate for Zn leaching effects after CdCl2 activation treatment. Analysis of the solar cell composition and structure by X-ray photoelectron spectroscopy depth profiling and X-ray diffraction showed that higher concentrations of Zn in the Cd1-xZnxS window layer resulted in suppression of S diffusion across the CdTe/Cd1-xZnxS interface after CdCl2 activation treatment. Excessive Zn content in the Cd1-xZnxS alloy preserved the spectral response in the blue region of the solar spectrum, but increased series resistance for the solar cells. A modest increase in the Zn content of the Cd1-xZnxS alloy together with a post-deposition air anneal resulted in an improved blue response and an enhanced open circuit voltage and fill factor. This device yielded a mean efficiency of 8.3% over 8 cells (0.25 cm2 cell area) and best cell efficiency of 8.8%

Inoculation theory in the post-truth era: Extant findings and new frontiers for contested science, misinformation, and conspiracy theories

Abstract: Although there has been unprecedented attention to inoculation theory in recent years, the potential of this research has yet to be reached. Inoculation theory explains how immunity to counter‐attitudinal messages is conferred by preemptively exposing people to weakened doses of challenging information. The theory has been applied in a number of contexts (e.g., politics, health) in its 50+ year history. Importantly, one of the newest contexts for inoculation theory is work in the area of contested science, misinformation, and conspiracy theories. Recent research has revealed that when a desirable position on a scientific issue (e.g., climate change) exists, conventional preemptive (prophylactic) inoculation can help to protect it from misinformation, and that even when people have undesirable positions, “therapeutic” inoculation messages can have positive effects. We call for further research to explain and predict the efficacy of inoculation theory in this new context to help inform better public understandings of issues such as climate change, genetically modified organisms, vaccine hesitancy, and other contested science beliefs such as conspiracy theories about COVID‐19

Using social and behavioural science to support COVID-19 pandemic response

The COVID-19 pandemic represents a massive global health crisis. Because the crisis requires large-scale behaviour change and places significant psychological burdens on individuals, insights from the social and behavioural sciences can be used to help align human behavior with the recommendations of epidemiologists and public health experts. Here we discuss evidence from a selection of research topics relevant to pandemics, including work on navigating threats, social and cultural influences on behaviour, science communication, moral decision-making, leadership, and stress and coping. In each section, we note the nature and quality of prior research, including uncertainty and unsettled issues. We identify several insights for effective response to the COVID-19 pandemic, and also highlight important gaps researchers should move quickly to fill in the coming weeks and months

Parental Involvement in National EFL Test Preparation

Parents, one of the primary stakeholders in their child’s performance in tests, can play a vital role in assessment. As these high-stakes tests are likely to bring life-changing consequences to students’ lives, most parents try their best to help their children to prepare for them. However, almost no research has explored the nature of parental involvement (PI) in preparing for high-stakes tests. This article reports on a study that explored PI in preparing their children for a national level English as a foreign language (EFL) test in the Nepalese context. Data was generated through a survey of 247 students, 72 oral diary entries and 24 interviews with six students and their parents. The data indicated a high level of PI in their children’s test preparation. Parents supported their children in various ways, such as creating a conducive learning environment at home, collaborating with neighbours and relatives, sharing their experiences, and teaching test preparation strategies. Parents even pressured their children into working for the test by controlling their non-academic lives in such a way that, during the test preparation time, children were not allowed to play and their time for sleeping was curtailed. A clear difference could be observed between the parents with university degrees and those who were illiterate in terms of the strategies they used to support their children in preparing for the test

Large area low cost processing for CIS photovoltaics. Final technical report

An ink coating method was developed for CIS absorber deposition. The technique involves four processing steps: (1) preparation of a Cu-In alloy powder, (2) preparation of an ink using this powder, (3) deposition of the ink on a substrate in the form of a precursor layer, and (4) selenization to convert the Cu-In precursor into a fused CIS film. Absorbers grown by this low-cost, large-area method were used in the fabrication of 10.5% efficient solar cells

Application of CIS to high-efficiency PV module fabrication. Phase 3 final technical report

During this research period, researchers at International Solar Electric Technology (ISET) concentrated their efforts on three different areas of research. Within the National CIS R and D Team, ISET participated in the substrate/Mo interactions working group and investigated issues such as Na diffusion from the soda-lime glass substrate into the Mo layers and CIS films. Researchers determined that the Na content within the Mo layers was not a strong function of the nature of the Mo film. However, they found that diffusion through the Mo layers was a function of the Mo film characteristics as well as a very strong function of the CIS growth process itself. Researchers showed conclusively that the Na resided on the grain boundaries of CIS layers. Another team activity involved evaluation of CdS-free CIS solar cells. ZnO/CIS junctions prepared by the two-stage process showed light-soaking effects. Cells left under illumination improved in efficiency and were similar to the CdS/CIS junctions. After storage in the dark, however, efficiency deteriorated greatly for the ZnO/CIS device, most of the decline coming from the open-circuit voltage values. Much of the effort during this period was spent on developing a low-cost, non-vacuum CIS deposition technique. The method developed involves particulate deposition and formation of precursor layers followed by the conversion of these layers into CIS. Test modules of 40--60 cm{sup 2} were adapted to understand the issues involved in this novel technology. At the present time, the submodule efficiencies are 6--7%. Single-cell efficiencies are in the 10--13% range