Pulsed Electrochemical Deposition of CuInSe2 and Cu(In,Ga)Se2 Semiconductor Thin Films

CuInSe2 (CIS) and Cu(In,Ga)Se2 (CIGS) semiconductors are the most studied absorber materials for thin films solar cells due to their direct bandgap and large absorption coefficient. The highly efficient CIGS devices are often fabricated using expensive vacuum based technologies; however, recently electrodeposition has been demonstrated to produce CIGS devices with high efficiencies and it is easily amenable for large area films of high quality with effective material use and high deposition rate. In this context, this chapter discusses the recent developments in CIS and CIGS technologies using electrodeposition. In addition, the fundamental features of electrodeposition such as direct current, pulse and pulse-reverse plating and their application in the fabrication of CIS and CIGS films are discussed. In conclusion, the chapter summarizes the utilization of pulse electrodeposition for fabrication of CIS and CIGS films while making a recommendation for exploring the group’s unique pulse electroplating method

Microstructural evolution in hot compressed TiHy 600 titanium alloy

TiHy 600 alloy is a near alpha titanium alloy, widely used for gas turbine engine applications such as disc and blades for high pressure compressors. One drawback of this alloy is that it is susceptible to cold dwell fatigue, which is due to the presence of micro-textured zones. Thus, appropriate processing parameters (i.e. temperature, strain and strain rate) are required to reduce the size of the micro-textured region. In order to find out the optimized processing parameters, hot compression tests were performed up to 50% engineering strain at temperatures range of 900oC-1050oC and strain rate range of 10-3 to 101 s-1 using thermo-mechanical simulator (Gleeble 3800®). Flow behavior characteristics were studied from the data obtained during hot compression and processing map was developed at true strain of 0.6 using Dynamic Materials Modeling (DMM) approach. Microstructural examination of deformed TiHy 600 titanium alloy were carried out at a particular strain rate of 10-3 s-1 and temperatures of 900oC, 950oC, 975oC, 1000oC and 1050oC. Microstructural examination consists of orientation image mapping along compression direction using electron backscatter diffraction. Hot compression mostly resulted into new dynamic recrystallized (DRX) alpha grains at 900oC, mixture of deformed large alpha grains containing subgrain boundaries and transformed beta phase consisting of secondary alpha laths at 950oC and 975oC and alpha laths transformed from deformed beta grains at 1000oC and 1050oC

Inkjet printed CuIn(1-X)GaXSe2 thin film by controlled selenium distribution for improved power conversion efficiency in chalcopyrite solar cells

Selenium (Se) vapor pressure is a key factor during the selenization of CuIn1-XGaX (CIG) film to obtain a high-quality CuIn1-XGaXSe2 (CIGS) absorber layer. To investigate the effect of Se vapor distribution on the grain growth of inkjet printed precursor film, two geometries of graphite box (square and circular) are used. The results revealed that selenization in the round graphite box give rise to uniform surface coverage and suppressed fine-grained layer due to adequate and uniform distribution of Se vapor. In contrast, film selenized in a square graphite box exhibits high strain and low crystallinity with a thick fine-grained layer. Probable Se vapor distribution inside the graphite box based on internal geometrical constraint and its impact on crystal phase and microstructure is discussed. Finally, CIGS devices fabricated using films selenized in a round graphite box demonstrates higher power-conversion efficiency of 5.2%, owing to high light absorption and efficient carrier separation. Based on J-V and EQE results, probable losses and recombination in the devices are examined and discussed. © 2021 The Author(s

Role of selenium content in selenization of inkjet printed CIGSe2 thin film solar cell

The presence of fine grained layer in Cu (In, Ga) Se 2 (CIGSe) thin film can largely impedes the performance of solar cell; problem was well identified in earlier reports however not researched and addressed systematically. In this context, present work proposes a systematic experimental strategy to reduce this fine grained layer thickness to a great extent, evident in improvement of final cell performance. CIG precursor layer was deposited by inkjet printing technique using an aqueous based ink followed by atmospheric selenization in rapid thermal annealing (RTP) furnace. A set of selenization experiments was carried out by varying the number of selenium pellets (2, 4 and 8) in a fixed volume of closed graphite box by keeping other selenization conditions (temperature and time) constant. In all cases, single phase CIGSe films with clear bi-layered structure were formed which were further analyzed by XRD, Raman and FESEM characterization techniques. It is understood that during selenization, Se flux is highly influential in forming bilayer structure with reduction in fine grain layer by increasing number of Se pallets. Reduction in fine grained layer led to improve the photoconversion efficiency from 1.05 % to 3.43 % of the CIGSe solar cells on an active area of 4mm x 4mm. Moreover, the samples prepared with high selenium flux exhibited MoSe 2 formation at the junction of CIGSe and Mo thin film

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

Fostering deep drawability through recrystallization texture strengthening in aluminum-rich interstitial free steel

The development of strong normal direction (ND)║〈111〉 fiber texture is crucial for deep drawability in interstitial free steels used for automotive applications. The present work focuses on comparative investigations on texture development, Lankford parameter measurement, microstructural evolution, recrystallization kinetics, and grain growth kinetics of titanium‑niobium stabilized interstitial free steels with different aluminum (Al) content. Industrially hot-rolled interstitial free steels with 0.06 wt% Al and 0.17 wt% Al were cold-rolled (∼90%), followed by isothermal annealing at 650 °C, 675 °C, and 700 °C for various time intervals. Texture studies using electron backscatter diffraction and X-ray diffraction showed the formation of a stronger ND fiber texture in 0.17 wt% Al steel compared to 0.06 wt% Al Steel after full recrystallization. A high rm value in 0.17 wt% Al steel than in 0.06 wt% Al Steel indicates the beneficial effects of Al addition in interstitial free steel. The study of recrystallization kinetics depicted faster recrystallization kinetics in interstitial free steel with 0.17 wt% Al. The grain growth kinetics of recrystallized grains illustrated similar behavior in both steels. At the onset of recrystallization in 0.06 wt% Al steel, a transient strengthening of the {001} 〈110〉 component (an effect of stress-induced boundary migration) was observed, which obstructed the nucleation of ND fiber grains. In contrast, the initial rapid nucleation of ND fiber grains in the 0.17 wt% Al steel was responsible for stronger ND fiber texture development. © 2022 Elsevier Inc

Adsorption-Driven Catalytic and Photocatalytic Activity of Phase Tuned In2S3 Nanocrystals Synthesized via Ionic Liquids

Phase tuned quantum confined In2S3 nanocrystals are accessible solvothermally using task-specific ionic liquids (ILs) as structure directing agents. Selective tuning of size, shape, morphology, and, most importantly, crystal phase of In2S3 is achieved by changing the alkyl side chain length, the H-bonding, and aromatic pi-stacking ability of the 1-alkyl-3- methylimidazolium bromide ILs, [C(n)mim]Br (n = 2, 4, 6, 8, and 10). It is observed that crystallite size is significantly less when ILs are used compared to the synthesis without ILs keeping the other reaction parameters the same. At 150 degrees C, when no IL is used, pure tetragonal form of beta-In2S3 appears however in the presence of [C(n)mim]Br [n = 2,4], at the same reaction condition, a pure cubic phase crystallizes. However, in case of methylimidazolium bromides with longer pendant alkyl chains such as hexyl (C-6), octyl (C-8) or decyl (C-10), nanoparticles of the tetragonal polymorph form. Likewise, judicious choice of reaction temperature and precursors has a profound effect to obtain phase pure and morphology controlled nanocrystals. Furthermore, the adsorption driven catalytic and photocatalytic activity of as-prepared nanosized indium sulfide is confirmed by studying the degradation of crystal violet (CV) dye in the presence of dark and visible light. A maximum of 94.8% catalytic efficiency is obtained for the In2S3 nanocrystals using tetramethylammonium bromide (TMAB) ionic liquid

Comprehensive Observations and Interpretations in Al-Rich Interstitial-Free High-Strength Steel via Process-Induced Structure Evolution

Developing ND parallel to fiber texture is vital for assessing the properties of interstitial-free high-strength steels utilized in the automotive industry. The present work deals with the microstructure and texture evolution in titanium-niobium-stabilized interstitial-free high-strength steels with varied aluminum content. Industrially hot-rolled steels with different aluminum content (0.045 and 0.12 wt.%) were cold-rolled (similar to 90%) and isothermally annealed at 650 and 750 degrees C for multiple time intervals. Texture studies showed a similarly weak hot band textures. After annealing, a stronger {111} recrystallization texture was observed in high-Al steel than in low-Al steel. High-Al steel depicted faster recrystallization than that of low-Al steel. In the early stages of recrystallization, a variation in the recrystallization behavior of the steels was observed. The presence of the strain-induced boundary migration at the beginning of annealing triggered recrystallization of 10011 grains and caused sluggish recrystallization of {111} grains in low-Al steel. In contrast, the rapid recovery of {111} fiber grains hindered the effect of strain-induced boundary migration in high-Al steel. It resulted in faster recrystallization of {111} and stronger {111} fiber texture. A higher annealing temperature and grain growth further strengthened the {111} fiber texture in both steels

Investigation on effects of precursor pre-heat treatments on CIGS formation using spin-coated CIG precursor

A low cost, non-vacuum process involving spin coating of metallic precursors followed by selenization was substantiated for the fabrication of CIGS (CuInxGa(1−x)Se2) thin film absorber. Spin coating of CIG precursors using environmentally benign solvents and studying the effects of various heat treatments on the spin-coated CIG precursor film leads to high-quality crystalline CIGS thin films with minimum carbon impurities. In this work, effects of various heat treatments of CIG precursor (heat treatment of precursor films after each individual run of spin coating using hot plate, using air dryer, without any pre-heat treatment and heating of 30-run coated sample on hot plate for 30 mins) followed by selenization has been investigated and being reported. The as-prepared CIGS thin film samples are characterized by X-ray diffraction (XRD), Raman spectroscopy (RS), Field emission scanning electron microscopy (FESEM), UV-Vis-IR spectroscopy and X-ray photo electron spectroscopy. From XRD pattern and Raman spectra, MoSe2 phase is also observed along with tetragonal chalcopyrite CIGS phase. Through FESEM and EDS, it is observed that heating each individual run has resulted a high-quality compact dense film with minimum carbon composition. XPS also confirms the minimum carbon composition in case of preheating individual run. From UV-Vis spectra, the bandgap of the prepared CIGS material is found to be 1.5 eV, essential for the cell fabrication

Quantitative prediction of Al and learning grain boundary character in Al-rich interstitial free steel

It is known that the addition of Al in interstitial free steel has a positive influence on the normal direction fiber recrystallization texture. The location and role of Al in interstitial free steel are not yet clear. Current research shows the likely role of Al in precipitation and/or its location in the grain matrix/grain boundary (0.17 wt% Al) and its impact on the properties. Industrially processed hot-rolled steel subjected to cold rolling (90%) and isothermal annealing validated the formation of normal direction fiber recrystallization texture. Precipitation studies showed no Al-containing precipitates. High-resolution secondary ion mass spectrometry imaging confirmed the presence of Al more on certain grain boundaries in fully recrystallized steel. Molecular statics simulation studies using a large-scale atom/molecular massively parallel simulator showed a reduction in the grain boundary energy with Al addition, assisting the system to reach a minimum energy state