Properties For Solar Cell Applications Research Articles

Structure and properties of CdS thin films prepared by pulsed laser assisted chemical bath deposition

Cadmium sulphide (CdS) is a well known n-type semiconductor having suitable optoelectronic properties for solar cell applications. In the present work, we report the preparation and characterization of CdS thin films by pulsed laser assisted chemical bath deposition (PLACBD). CdS thin films were synthesized from a chemical bath containing cadmium chloride, triethanolamine, ammonium hydroxide and thiourea at different conditions. The thin films were prepared by in situ irradiation of the chemical bath using a Q-switched Nd:YAG laser with two different output wavelengths (532nm and 1064nm). The thin films deposited for 10, 15 and 20min were characterized by X-ray diffractometry (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Atomic force microscopy (AFM), UV⿿vis absorption spectroscopy and photoconductivity measurements. Our results showed that in-situ irradiation of the chemical bath using pulsed laser resulted accelerated growth of the CdS thin films.

Pyrite‐Based Bi‐Functional Layer for Long‐Term Stability and High‐Performance of Organo‐Lead Halide Perovskite Solar Cells

Organo‐lead halide perovskite solar cells (PSCs) have received great attention because of their optimized optical and electrical properties for solar cell applications. Recently, a dramatic increase in the photovoltaic performance of PSCs with organic hole transport materials (HTMs) has been reported. However, as of now, future commercialization can be hampered because the stability of PSCs with organic HTM has not been guaranteed for long periods under conventional working conditions, including moist conditions. Furthermore, conventional organic HTMs are normally expensive because material synthesis and purification are complicated. It is herein reported, for the first time, octadecylamine‐capped pyrite nanoparticles (ODA‐FeS2 NPs) as a bi‐functional layer (charge extraction layer and moisture‐proof layer) for organo‐lead halide PSCs. FeS2 is a promising candidate for the HTM of PSCs because of its high conductivity and suitable energy levels for hole extraction. A bi‐functional layer based on ODA‐FeS2 NPs shows excellent hole transport ability and moisture‐proof performance. Through this approach, the best‐performing device with ODA‐FeS2 NPs‐based bi‐functional layer shows a power conversion efficiency of 12.6% and maintains stable photovoltaic performance in 50% relative humidity for 1000 h. As a result, this study has the potential to break through the barriers for the commercialization of PSCs.

Effect of sputter deposited Zn precursor film thickness and annealing time on the properties of Cu2ZnSnS4 thin films deposited by sequential reactive sputtering of metal targets

Cu2ZnSnS4 (CZTS) is made of earth abundant elements and also have suitable optical properties for solar cell applications. But, in phase diagram, CZTS exists in a narrow range of temperature and composition. Therefore, optimizing the elemental composition and annealing time is very important for obtaining phase pure CZTS. In this study, the effects of elemental composition and short annealing time on the structural and optical properties of reactively sputtered CZTS thin films are reported. Thin films were deposited by reactive sputtering of Cu: Sn (60:40wt%), Sn and Zn targets sequentially in the presence of H2S at room temperature. Amount of Zn precursor was varied by changing the sputter time for Zn. The films were rapidly annealed in inert atmosphere for varying time. The band gap of sample changed with change in the composition as well as annealing time. Sample with higher Zn content showed better crystallinity. With increase in the annealing time the crystallinity of samples improved. Sample annealed for 12min at 550°C was phase pure. Obtaining good quality film even for very short anneal time is the novelty of reactive sputtering method as all the elements are already mixed and short annealing is required only for crystal growth. Through detailed experiments, the optimum composition and annealing time required for the growth of phase pure CZTS has been established.

Optimization of CBD-CdS physical properties for solar cell applications considering a MIS structure

While the standard interpretation treats CdS/CdTe, CdS/Cu(In,Ga)Se2(CIGSe) and CdS/kesterites as p-n junctions, some recent reports suggest these solar cells operate rather as a Metal-Insulator-Semiconductor (MIS) structure. In this paper, we report results about the dependence of electrical, optical, morphological and structural properties of CBD-CdS on growth conditions in order to obtain the best layers to be used in solar cells according to the MIS model. In particular, CBD-CdS thin films were synthesized by changing the complexing agents in the bath solution, the Cd source and the nominal S/Cd ratio. In order to study the impact of the different CdS deposition approaches, CIGSe and CZTSe solar cells were processed. The influence of CdS:Cu as well as Cd sources such as Cd(NO3)2 and CdSO4 on solar cell electrical parameters is studied.

Simple Vacuum Evaporation Route to BaSi2 Thin Films for Solar Cell Applications

The BaSi2 semiconductor has excellent optoelectronic properties for solar cell applications and consists of earth-abundant elements. In this study, we have investigated the thin film growth of BaSi2 by a simple vacuum evaporation technique. It is shown by X-ray diffraction that single-phase BaSi2 films can be formed at high substrate temperatures of 500 and 600 ˚C on either Si(111) or EAGLE XG glass substrate. The film growth mechanism is discussed on the basis of the transmission electron microscopy observation and energy-dispersive X-ray spectra of the film and the residue of evaporation source. It is concluded that high substrate temperatures are needed to remove excess Ba atoms and to eliminate a composition gradient. In addition, suitable optical properties for solar cell applications are revealed by analyzing the transmittance and reflectance spectra.

Comparative studies of structural and electrical properties of co-doped ZnO thin films prepared by direct current sputtering as a front contact for copper indium gallium di-selenide solar cell

Doped and co-doped ZnO thin films are currently under intense investigation and development for optoelectronic and solar cell applications. Here in this study Aluminum and Boron (ZAB), Gallium and Boron (ZGB), and Gallium and Aluminum (ZGA) co-doped ZnO thin films were deposited on glass substrate using DC magnetron sputtering at room temperature. A comparative study of the above co-doped ZnO thin films was done on the basis of its structural and electrical properties for solar cell application. All thin films have shown excellent optical properties with more than 80% transmission in the visible range of the light. From the X-ray diffraction patterns, it is found that the films were polycrystalline in nature and the ZAB thin film is more crystalline than the other co-doped ZnO thin films. The surface morphology showed different growth structure of the films. For ZAB and ZGA thin films, the rounded grains were observed and for ZGB thin film some rounded as well as corn type grains were observed. The electrical properties of all the thin films were measured using Hall measurement system at room temperature. For ZGB and ZGA thin films, the resistivity was obtained in the order of 10−3 ohm cm and for ZAB thin film the lowest resistivity of the order of 10−4 ohm cm was obtained which is ideal for transparent conducting oxide thin films to be used as window cum-front contact in multi-junction solar cell such as CIGS solar cell.

Morphological Manipulation of Solvothermal Prepared CdSe Nanostructures by Controlling the Growth Rate of Nanocrystals as a Kinetic Parameter

The morphological manipulation, structural characterization, and optical properties of different cadmium selenide (CdSe) nanostructures are reported. Two different CdSe nanostructures, i.e., nanorods and nanoparticles, were grown by controlling the concentration of precursors (i.e., cadmium nitrate and selenium dioxide) in ethanolamine solvent. By manipulating the kinetic parameter of the process (i.e., growth rate) under constant growth driving force (i.e., degree of supersaturation), the morphology of CdSe nanostructures can be tailored from nanorods to nanoparticles. The optical properties of CdSe nanostructures were investigated using ultraviolet–visible (UV-vis) spectroscopy. The absorption edge of the samples showed a blue-shift. CdSe nanostructures prepared under optimized conditions showed good microstructural and optical properties for solar cell applications.

Tailoring of morphology and crystal structure of CdSe nanostructures by controlling the ratio of triethylenetetraamine and water in their mixed solution

The morphological manipulation, structural characterization, and optical properties of different CdSe nanocrystals were reported. Several different CdSe nanostructures, including nanowires, tetrapod crystals, and nanoparticles were grown by varying the volume ratio of triethylenetetraamine (TETA) and water (WA) in their mixed solution. By manipulating the growth driving force (i.e., the degree of supersaturation) and kinetics of the process (i.e., growth rate), the morphology and crystal structure of CdSe nanocrystals can be tailored. Growth driving force changed their morphology from nanowires to tetrapod structures and from the latter structure to nanoparticles. Moreover, kinetics of the process altered their crystal structure from wurtzite to zinc blende. The optical property of CdSe nanocrystals was investigated using UV-vis spectroscopy. The absorption edge of CdSe nanostructures showed a blue shift. CdSe nanocrystals prepared under optimized conditions showed good microstructural and optical properties for solar cell application.

Crystallization Behavior of Silicon Quantum Dots in a Silicon Nitride Matrix

Silicon quantum dot superlattice was fabricated by alternating deposition of silicon rich nitride (SRN) and Si3N4 layers using RF magnetron co-sputtering. Samples were then annealed at temperatures between 800 and 1,100 degrees C and characterized by grazing incident X-ray diffraction (GIXRD), transmission electron microscopy (TEM), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). GIXRD and Raman analyses show that the formation of silicon quantum dots occurs with annealing above 1,100 degrees C for at least 60 minutes. As the annealing time increased the crystallization of silicon quantum dots was also increased. TEM images clearly showed SRN/Si3N4 superlattice structure and silicon quantum dots formation in SRN layers after annealing at 1,100 degrees C for more than 60 minutes. The changes in FTIR transmission spectra observed with annealing condition corresponded to the configuration of Si-N bonds. Crystallization of silicon quantum dots in a silicon nitride matrix started stabilizing after 60 minutes' annealing and approached completion after 120 minutes'. The systematic investigation of silicon quantum dots in a silicon nitride matrix and their properties for solar cell application are presented.

Investigation of Bonding Characteristics Between Si Quantum Dots and a SiO2 Matrix

In order to understand and control the properties of Si quantum dot (QD) superlattice structures (SLS), it is necessary to investigate the bonding between the dots and their matrix and also the structures' crystallinities. In this study, a SiOx matrix system was investigated and analyzed for potential use as an all-silicon multi-junction solar cell. Si QD SLS were prepared by alternating deposition of Si rich SiOx (x = 0.8) and SiO2 layers using RF magnetron co-sputtering and subsequent annealing at temperatures between 800 and 1,100 degrees C under nitrogen ambient. Annealing temperatures and times affected the formation of Si QDs in the SRO film. Raman and FTIR spectra revealed that nanocrystalline Si QDs started to precipitate after annealing at 1,100 degrees C for 1 hour. TEM images clearly showed SRO/SiO2 SLS and Si QDs formation in SRO layers after annealing at 1,100 degrees C for 2 hours. XPS analysis showed that Si-Si and Si-O bonding changes occurred above 1,100 degrees C. XPS analysis also revealed that Si QD SLSs started stabilizing after 2 hours' annealing and approached completion after 3 hours'. The systematic investigation of Si QDs in SiO2 matrices and their properties for solar cell application are presented.

Defect Processes in a PbS Metal Organic Framework: A Quantum-Confined Hybrid Semiconductor

We report the effects of reduced dimensionality and organic networks on defect reactions in a hybrid solid of PbS (galena). Through first-principles calculations, we demonstrate that formation of the organic−inorganic network increases both the band gap and defect reaction energies. Remarkably, anion vacancies result in a localized defect center in both the bulk and hybrid materials, with high ionization energies deep in the band gap, while cation vacancies provide low energy shallow acceptor levels; the hybrid system will favor intrinsic p-type conductivity. The results demonstrate the feasibility of utilizing hybrid solids to engineer material properties for solar cell applications.

Effects of pulsed sputtering frequency on the uniformity of Al:ZnO’s transparent conductive oxide properties for solar cell applications

Bipolar pulsed magnetron sputtering is used to deposit Al doped ZnO (AZO) on a glass substrate for a transparent conducting oxide in a solar cell structure. A 5×25in.2 AZO target was sputtered by 50–250kHz bipolar pulsed dc power supply to deposit a 400×400mm2 area by swinging back and forth. Sheet resistance, surface morphology, and optical transmittance were measured at different positions on 16 witness samples (small glass slides) to evaluate uniformity. In the thickness of 800nm, the average value of sheet resistance was 30Ω∕◻ and the average resistivity was 2.1×10−3Ωcm. Transmittance was 50%–80% over the visible range. The nonuniformities of thickness, transmittance, and resistivity in the 400×400mm2 area were 5.8%, 0.8%, and within 9.5%, respectively.

Influence of the Heating Mode and the Spray Introduction on Chemically Vapour Deposited Aluminium Doped Zinc Oxide Thin Films

Aluminium doped zinc oxide films were deposited by spray pyrolysis using zinc acetate and aluminium pentanedionate as precursor and doping agent respectively. The aim was to determine the best way for introducing the spray and for heating the glass substrate. As-deposited films are characterized according to their structural, electrical and optical properties for solar cell applications. The growth rate was also taking into account as the deposition process must be a low cost one. We used of a new liquid injection head allowing to introduce an aerosol of very small droplets horizontally into the reactor. We showed that infrared heating can be an interesting alternative to the common generally used hot plate. We obtained Al:ZnO films with a growth rate of 0.358 nm/s and a figure of merit of 1.7 10-3Ω-1.

Transition from amorphous to microcrystalline Si:H: effects of substrate temperature and hydrogen dilution

Structural changes in silicon films with variations of hydrogen dilution and substrate temperature have been studied. At a critical value of hydrogen dilution in silane ( φ) a sharp transition from amorphous to microcrystalline phase has been observed. An increase of substrate temperature from 170 to 340 °C shifts the transition point from φ=95.5% to 93.5%. The change in dark conductivity and absorption corroborate with the change in crystalline volume fraction in the films. The grain size varies from 45 to 360 Å depending on deposition conditions. Optical absorption and hydrogen content in the film decreases drastically with formation of microcrystalline structure. Silicon films developed at 340 °C show moderate photosensitivity together with low light induced degradation at low crystallinity, which might be suitable properties for solar cell application.

Hydrogenated microcrystalline silicon: how to correlate layer properties and solar cell performance

Undoped hydrogenated microcrystalline silicon (μc-Si:H) layers and cells have been deposited by plasma chemical vapour deposition at low temperature at different powers and silane dilutions. Electronic transport properties and defect density of the layers have been compared to the cell performances to identify the important material properties for solar cell applications. A correlation is found between the defect density, μ 0 τ 0 quality parameter, and cell efficiency. Anisotropy of the transport properties in some μc-Si:H is also demonstrated.

Structural and electrical properties of silicon epitaxial layers grown by LPE on highly resistive monocrystalline substrates

The present paper reports on the properties of liquid-phase epitaxy (LPE) silicon layers grown on monocrystalline highly resistive (1 0 0)-oriented float zone (FZ) silicon substrates. All layers were grown in an indium/gallium solution saturated with Si at temperatures near 920°C. For the optimisation of layer properties for solar cell applications, parameters such as growth rate and Ga concentration of the In solution were varied. Hall measurements, X-ray spectroscopy, mechanical surface profiling (Dektak) and a lifetime analyser were used to characterise the 100–200 μm thick LPE layers.