Sb2S3 solar cells with TiO2 electron transporting layers synthesized by ALD and USP methods

Abstract

Electronic characteristics were investigated for solar cells (SCs) based on FTO/TiO₂/Sb₂S₃/P3HT/Au structure, employing TiO₂ electron transport layers (ETLs) fabricated by two different methods: ultrasonic spray pyrolysis (USP) and atomic layer deposition (ALD). Regardless of the deposition method, both ALD and USP-TiO₂ exhibit the anatase crystal structure. The calculated crystallite sizes, derived from the (101) reflection of TiO₂ layers using the Scherrer equation, show minimal variance between the two methods, with values 25 nm for USP and 30 nm for ALD TiO₂, respectively. Optical band gaps (E_g) were found to be 3.31 eV and 3.35 eV for USP and ALD methods, respectively. Exploring the thickness series of ALD-TiO₂, ranging from 100 to 1000 cycles (approximately 5–75 nm), solar cell performance was evaluated, with the highest power conversion efficiency (PCE) of 3.3 % achieved using ALD-TiO₂ of 400 cycles (approximately 30 nm thick). Notably, SCs featuring USP TiO₂ ETL layers, with a thickness of approximately 35–40 nm, outperform their ALD-TiO₂ counterparts, improving PCE by 15 %, recording 4.0 % versus 3.3 %, respectively. This superiority in PCE is attributed to the more favorable conduction band minimum (CBM) position of USP-TiO₂ relative to the Fermi level, as revealed in the band diagram. Specifically, a lower CBM spike at the USP-TiO₂/-Sb₂S₃ interface indicates reduced recombination rates compared to those at the ALD-TiO₂/-Sb₂S₃ interface. This study offers valuable insights into enhancing SC performance by optimizing deposition methods and synthesis parameters of ETL layers.