Determination of carrier lifetime in thermally evaporated In 2 S 3 thin films by light induced transient grating techniq

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Determination of carrier lifetime in thermally evaporated ­In2S3 thin films by light induced transient grating technique S. Rasool1 · P.  Ščajev3 · K. Saritha1 · I. Svito2 · K. T. Ramakrishna Reddy1 · M. S.  Tivanov2 · V. Grivickas3 Received: 29 November 2019 / Accepted: 23 March 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020

Abstract In2S3 thin films were deposited onto soda lime glass substrates using thermal evaporation technique at a constant substrate temperature of 300 °C and the films were annealed in a sulfur ambient at 250 °C and 300 °C for 1 h. Light induced transient grating (LITG) technique was used to determine the carrier lifetime in ­In2S3 thin films. The determined carrier lifetime values for different excitation energy densities, I0 = 0.06–1.64 mJ/cm2 decreased from 206  to 18 ps and 150 to 14 ps for the films annealed at 250 °C and 300 °C respectively. Further, the bimolecular, Auger recombination coefficients and diffusion coefficient were determined in the films. The observed bimolecular carrier recombination origin was explained by interface and Auger recombination processes. Keywords In2S3 films · LITG · Carrier lifetime · Bimolecular coefficient · Auger coefficient

1 Introduction Cu(In,Ga)Se2 (CIGSe) and CdTe-based solar cells have reached high conversion efficiencies of 22.6% and 22.1% using CdS as a buffer layer [1, 2] and are currently commercialized. But, the large scale production of these solar cells using CdS is environmentally unsafe to handle because of the toxicity of cadmium. Therefore, alternate materials are of much interest now that can successfully replace CdS. In this context, ­In2S3 is a potential alternative material, because of its wide energy band gap (2.0–3.3 eV), n-type conductivity, non-toxic and photoconductive nature [3–6]. Recently, Spiering et al. [7] reported a record solar cell efficiency of 18.2% using evaporated ­In2S3 thin film as a buffer layer for Cu(In,Ga)Se2-based thin film solar cells. Charge carrier lifetime is one of the important parameters that significantly influence the performance of * K. T. Ramakrishna Reddy [email protected] 1



Solar Photovoltaic Laboratory, Department of Physics, Sri Venkateswara University, Tirupati, Andhra Pradesh 517 502, India

2



Faculty of Physics, Belarusian State University, Nezavisimosti 4 Av, 220030 Minsk, Belarus

3

Institute of Photonics and Nanotechnology, Vilnius University, Sauletekio ave. 3, LT‑10257 Vilnius, Lithuania



optoelectronic devices. Determination of carrier lifetime and carrier diffusion length of the material is highly essential before fabrication of any device. Generally, carrier lifetime is sensitive to impurities or defects that are present in the material. In direct band gap semiconductors, the lifetime of charge carriers is of the order of nanoseconds to microseconds, depending upon the excess carrier concentration and defect properties. The measurement of carrier lifetime is based on the dynamics of excess photo-generated charge carriers. Various techniques such a