Optical and photoelectric properties of lamellar nanocomposites obtained by Cd intercalation of GaTe

Date du colloque : 05/2013 International audienc

Development of Bi2S3 thin film solar cells by close-spaced sublimation and analysis of absorber bulk defects via in-depth photoluminescence analysis

This study was funded by the Estonian Research Council projects PSG689 “Bismuth Chalcogenide Thin-Film Disruptive Green Solar Technology for Next Generation Photovoltaics”, PRG627 “Antimony chalcogenide thin films for next-generation semi-transparent solar cells applicable in electricity producing windows”, and PRG1023; the Estonian Centre of Excellence project TK141 (TAR16016EK, TAR16016) “Advanced materials and high-technology devices for energy recuperation systems”, and the European Union's H2020 programme under the ERA Chair project 5GSOLAR grant agreement No 952509.The emergence of new PV applications in society requires the design of new materials and devices based on green and earth-abundant elements, with a different set of properties and wider applicability. In this perspective, Bi2S3 semiconductor material have gained attention as a defect-tolerant, non-toxic, and highly stable material for earth-abundant thin film PV technologies. Related to Bi2S3 non-toxic nature, so far it has been very popular to synthesize the material by chemical solution routes, while little research efforts have been dedicated to absorber deposition by physical deposition techniques. In particular, there are no studies on absorber development via rapid, high-volume, and in-line close-spaced sublimation technique. Moreover, in-depth analysis of material defects employing low temperature-dependent photoluminescence (PL) remains largely unexplored. In this work, we systematically study the impact of close-spaced sublimation (CSS) conditions on Bi2S3 absorber growth on various substrates, employing a wide range of source (400–600 °C) and substrate (200–400 °C) temperatures. CSS source temperature of 550 °C and substrate temperature of 400–450 °C were identified as optimal temperatures (grown either on glass, TiO2, or CdS substrates), allowing the fabrication of uniform and dense Bi2S3 films with enhanced [221]-oriented grains. For the first time, a proof of concept solar cell with CSS Bi2S3 is demonstrated and an in-depth analysis on the interrelation between grain structure, interface recombination, and device performance is provided. Employing low-temperature dependence PL, new and complementary insights on possible defects and recombination mechanisms are presented.--//-- M. Koltsov, S.V. Gopi, T. Raadik, J. Krustok, R. Josepson, R. Gržibovskis, A. Vembris, N. Spalatu, Development of Bi2S3 thin film solar cells by close-spaced sublimation and analysis of absorber bulk defects via in-depth photoluminescence analysis, Solar Energy Materials and Solar Cells, Volume 254, 2023, 112292, ISSN 0927-0248, https://doi.org/10.1016/j.solmat.2023.112292.(https://www.sciencedirect.com/science/article/pii/S0927024823001137) Published under the CC BY-NC-ND licence.Estonian Research Council projects PSG689, PRG627 and PRG1023; Estonian Centre of Excellence project TK141 (TAR16016EK, TAR16016); the European Union's H2020 programme under the ERA Chair project 5GSOLAR grant agreement No 952509; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2

Low processing temperatures explored in Sb2S3 solar cells by close-spaced sublimation and analysis of bulk and interface related defects

This study was funded by the Estonian Research Council project PRG627 “Antimony chalcogenide thin films for next-generation semi-transparent solar cells applicable in electricity producing windows”, the Estonian Research Council project PSG689 “Bismuth Chalcogenide Thin-Film Disruptive Green Solar Technology for Next Generation Photovoltaics”, the Estonian Centre of Excellence project TK141 (TAR16016EK) “Advanced materials and high-technology devices for energy recuperation systems”, and the European Union's Horizon 2020 ERA Chair project 5GSOLAR (grant agreement No. 952509). The article is based upon work from COST Action Research and International Networking project "Emerging Inorganic Chalcogenides for Photovoltaics (RENEW-PV)," CA21148, supported by COST (European Cooperation in Science and Technology); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD 01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2.Antimony trisulfide (Sb2S3) is a promising photovoltaic absorber, which has so far been fabricated mainly by chemical deposition methods. Despite its aptness for congruent sublimation, less research efforts have been made on low-temperature Sb2S3 processing by physical methods. In this regard, recent studies show large variation in the processing temperature of Sb2S3 films, which overall brings into question the need for higher substrate temperatures (>350 °C). Furthermore, in-depth analysis of defect structure of Sb2S3 employing temperature-dependent admittance spectroscopy (TAS) and photoluminescence (PL) remains largely unexplored. In this work, we systematically study the effect of close-spaced sublimation (CSS) substrate temperature on Sb2S3 absorber growth, employing a wide temperature range of 240–400 °C. Temperatures above 320 °C caused cracking phenomena in the Sb2S3 absorber film, proving the unviability of higher processing temperatures. CSS processing temperature of 300 °C was found optimal, producing crack-free Sb2S3 films with increased presence of (hk1) planes, and achieving the best CdS/Sb2S3 device with photoconversion efficiency of 3.8%. TAS study revealed two deep defects with activation energies of 0.32 eV and 0.37 eV. Low-temperature PL measurement revealed a band-to-band emission at 1.72 eV and a broad band peaked at 1.40 eV, which was assigned to a donor-acceptor pair recombination. Temperature-dependent I-V analysis showed that recombination at CdS–Sb2S3 interface remains a large limitation for the device efficiency. --//-- R. Krautmann, N. Spalatu, R. Josepson, R. Nedzinskas, R. Kondrotas, R. Gržibovskis, A. Vembris, M. Krunks, I. Oja Acik, Low processing temperatures explored in Sb2S3 solar cells by close-spaced sublimation and analysis of bulk and interface related defects, Solar Energy Materials and Solar Cells, Volume 251, 2023, 112139, ISSN 0927-0248, https://doi.org/10.1016/j.solmat.2022.112139. (https://www.sciencedirect.com/science/article/pii/S0927024822005566) Published under the CC BY licence.Estonian Research Council project PRG627; Estonian Research Council project PSG689; Estonian Centre of Excellence project TK141 (TAR16016EK); European Union's Horizon 2020 ERA Chair project 5GSOLAR (grant agreement No. 952509; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD 01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2

A post deposition annealing approach for organic residue control in TiO2 and its impact on Sb2Se3 TiO2 device performance

We report a systematic investigation on the influence of two step post deposition treatments PDTs on TiO2 buffer layers deposited by ultrasonic spray pyrolysis USP for emerging Sb2Se3 photovoltaics. Air annealing is a typical method for recrystallizing chemically deposited TiO2 films. However, organic residues such as carbon species from a precursor solution based on titanium tetraisopropoxide and acetylacetone may still remain on the TiO2 surface, therefore requiring an additional annealing step. We demonstrate that vacuum annealing can be a suitable technological approach to decrease the concentration of carbon species in TiO2 films. Vacuum annealing was performed at temperatures at 160 450 C prior to the 450 C air annealing step. It was found that vacuum annealing at 160 C followed by subsequent air annealing led to better device performance. This was explained by achieving an optimal balance between the removal of carbon content during vacuum annealing and the active recrystallization of TiO2 during air annealing. The decrease of carbon concentration by employing the two step approach was supported by changes in the lattice parameters of TiO2 and proven by X ray photoelectron spectroscopy XPS . The given study provides experimental evidence on how nanoscale carbon species in the TiO2 heterojunction partner layer of a Sb2Se3 solar cell can affect the device s performance. By this approach, we generate complementary insights on how the quality of the main interface has an impact and can take a key role despite the optimized Sb2Se3 grain structure and orientatio

Synthesis Control of Charge Separation at Anatase TiO2 Thin Films Studied by Transient Surface Photovoltage Spectroscopy

For the efficient photocatalytic oxidation of organic pollutants at surfaces of semiconductors, photogenerated holes shall be separated toward the surface and transferred to reactive surface sites, whereas the transfer of photogenerated electrons toward the surface shall be minimized. In this Research Article, the identification of suitable synthesis control of charge separation combined with an in depth understanding of charge kinetics and trapping passivation mechanisms at the related surfaces can provide tremendous opportunities for boosting the photocatalytic performance. In this work, a comprehensive transient surface photovoltage spectroscopy study of charge separation at anatase TiO2 thin films, synthesized by ultrasonic spray pyrolysis from titanium IV isopropoxide TTIP acetylacetone AcacH based precursor is reported. By varying the amount of AcacH in the precursor solution, an experimental approach of synthesis control of the charge transfer toward TiO2 surface is provided for the first time. An increased amount of AcacH in the precursor promotes transition from preferential fast electron to preferential fast hole transfer toward anatase surface, correlating with a strong increase of the photocatalytic decomposition rate of organic pollutants. Suitable mechanisms of AcacH induced passivation of electron traps at TiO2 surfaces are analyzed, providing a new degree of freedom for tailoring the properties of photocatalytic system

Optical and photosensitive properties of lamellar nanocomposites obtained by Cd intercalation of GaTe

By Cd-vapor heat treatment, at temperatures from 623 to 833 K, of GaTe single crystals, GaTe-CdTe composite is formed. CdTe amount is increasing together with heat treatment temperature. Absorption, photoconductivity and photoluminescence spectra of the composite contain particularities characteristic to GaTe and CdTe components. The absorption and photoconductivity edges display two thresholds at 1.66 eV (GaTe) and 1.50 eV (CdTe). Short lifetime recombination states form at the surface of composite samples, leading to narrowing of the photoconductivity bands in the high energy region, up to 1.8 eV. Widening of the absorption and photoconductivity bands in the low energy region is determined by absorption processes taking place in both GaTe and CdTe components

ZnO NiO heterostructures with enhanced photocatalytic activity obtained by ultrasonic spraying of a NiO shell onto ZnO nanorods

Degradation of organic pollutants such as methylene blue MB from water resources is currently of particular interest. Employment of a heterojunction device with optimized layer properties and proper interface engineering can enhance the photocatalytic performance by taking advantage of efficient charge separation. In this work, we develop an efficient photocatalytic system for the MB degradation based on ZnO nanorod ZnONR NiO core shell heterostructure with an optimized chemical and electronic structure for achieving record MB degradation efficiency of 70 . ZnONR were grown by hydrothermal technique, whereas homogeneous crystalline NiO thin films were prepared by a robust and easy for up scaling method of ultrasonic spray pyrolysis USP . The optimum preparation conditions of photocatalytically efficient ZnONR NiO heterostructures imply NiO film deposition from two USP cycles at 500 C followed by air annealing heterostructures at 600 C. The photocatalytic performance of ZnONR NiO core shell structure was investigated in comparison to counterpart layers and ZnO NiO bilayer system. Chemical composition and band alignment at the ZnONR NiO interface were investigated by X ray photoelectron spectroscopy, Kelvin probe and photoelectron yield spectroscopy. Current transport studies indicated the presence of built in electric field at the n ZnO p NiO heterointerface responsible for the enhanced photocatalytic activity and based on this the degradation mechanism of MB is discusse

Analysis of grain orientation and defects in Sb2Se3 solar cells fabricated by close spaced sublimation

The performance of a superstrate TiO2 Sb2Se3 solar cell, fabricated by close spaced sublimation technique CSS , was improved after the deployment of a seed layer. The seed layer caused columnar Sb2Se3 film growth with texture coefficient analysis TC showing increased presence of crystal planes, which are inclined towards the [001] crystal direction. Given the highly anisotropic properties of Sb2Se3, preferential growth of Sb4Se6 n rib bons along the [001] direction is best suited for effective charge collection. Hence, grain orientation of Sb2Se3 films was studied more closely via measurement of pole figures by XRD and orientation distribution maps by electron backscatter diffraction EBSD . Although the measurements did not reveal strong preferred orientation, it was observed that the columnar Sb2Se3 growth enhanced texture along the [001] direction. Temperature dependent admittance spectroscopy TAS and capacitance voltage CV profiling were performed on the seed assisted TiO2 Sb2Se3 solar cell to evaluate carrier density and deep defects in the Sb2Se3 absorber. TAS study revealed a deep defect with activation energy of 0.39 eV. CV profiles indicated that the density of defects could be as high as 1017 c

Combinative solution processing and Li doping approach to develop p type NiO thin films with enchanced electrical properties

The deposition of nickel oxide NiOx thin film from an acetylacetonate source using many solution based techniques has been avoided owing to its poor solubility in alcohol solvents. From this perspective, this work provides a systematic investigation of the development of NiOx thin film, using a combinative approach of ultrasonic spray pyrolysis USP and Li dopant for the synthesis and optimization of structural and optoelectronic properties of the films. An in depth comparative analysis of nickel acetylacetonate based precursor, employing acetonitrile and methanol as solvents, is provided. It is demonstrated that USP from acetylacetonate precursor yielded uniform, well compact, and transparent films, with polycrystalline cubic NiOx crystal structures. By screening the deposition temperature in the range of 300 450 C, a temperature of 400 C was identified as an optimal processing temperature leading to uniform, compact, highly transparent, and p type conductive films. At optimized deposition conditions 400 C , lithium doped NiOx Li NiOx thin film was deposited. The shift of the main 200 XRD peak position from 43.48 0 Li NiOx to 43.56 60 Li NiOx indicated Li incorporation into the NiOx lattice. An X ray photoelectron spectroscopy XPS study was employed to unravel the incorporation of Li into the deposited Li NiOx thin films. With the deconvolution of the Ni 2p core level for the as deposited 0, 60 Li NiOx films, the intensity of Ni3 related peak was found to increase slightly with Li doping. Furthermore, all the deposited Li NiOx thin films showed p type conductivity behavior, and the resistivity was reduced from 104 amp; 937;cm 0 Li NiOx to 102 amp; 937;cm 60 Li NiOx . Based on these results, the deposited NiOx and Li NiOx thin films suggested that USP deposited Li NiOx is highly suitable for application in inverted structure solar cells as the hole transport laye