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

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

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