Reduced energy band offset between photoanode and dye in SnO 2 -based DSCs with Cu doping
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ORIGINAL PAPER
Reduced energy band offset between photoanode and dye in SnO2-based DSCs with Cu doping Y B Liu, S B Zou, J H Duan*
, W Q Liu and H M Wu
Engineering Laboratory for Optoelectronics Testing Technology and School of the Testing and Photoelectric Engineering, Nanchang Hangkong University, Nanchang 330063, People’s Republic of China Received: 10 December 2019 / Accepted: 29 June 2020
Abstract: Tin oxide (SnO2) film is a promising photoanode for dye-sensitized solar cells (DSCs) with excellent optical and electrical properties as well as facile accessibility. Highly efficient DSCs require a fast charge transfer from dye to SnO2 in order to reduce the recombination from trap states. Herein, we report a Cu-doped SnO2 film as a photoanode for DSCs with faster charge transfer and higher efficiency. Ultraviolet photoelectron spectroscopy study indicates that conduction band of the Cu-doped SnO2 is adjusted from - 4.75 to - 4.57 eV via 5 at.% Cu concentrations. By adjusting the Cu concentrations, energy offset between the SnO2 and dye is reduced, which accelerates the charge transfer. Power conversion efficiency of the DSCs with optimized Cu-doped SnO2 achieves 4.01%, which is 61.7% higher than its counterpart without Cu doping. Keywords: Cu-doped SnO2; DSCs; Energy band offset
1. Introduction Since O’Regan and Gra¨tzel began the seminal work on DSCs in 1991 [1], PCE of DSCs has increased at a rapid pace from 7.1% in 1991 to 13% in 2014 [2]. The photoanode plays a critical role in determining the performance of DSCs. In particular, nanostructured photoanodes with a large surface area, high electron transfer efficiency and low electron recombination facilitate the preparation of high-performance DSCs. Many semiconductor materials, such as TiO2 [3, 4], ZnO [5, 6], SnO2 [7, 8] and BaSnO3 [9], have been used as photoanode in DSCs. SnO2 is a promising photoanode owing to its high electron mobility (125–250 cm2/V-1S-1) and wide band gap (3.62 eV, at room temperature), which indicates a faster transport of photogenerated electrons and higher long-term stability of electrons [10]. However, CB value of SnO2 is relatively low, which limits its application in DSCs. To solve the low intrinsic value of CB energy level [11], band gap engineering has been proposed as one of the most effective strategies. To alter the band gap of photoanode, many efforts have been explored such as doping with appropriate metal, which may modulate the electrical and optical
properties of the photoanode. In terms of photoanode materials for DSCs, several research groups reported on the studies of some metal (such as Al, Mg, Zn and Sb)-doped SnO2 nanoparticle [12–17]. Aponsu et al. [18] reported the DSCs based on Au-doped SnO2 photoanode with a highest efficiency of PCE * 3.9% at optimized concentration. Li et al. [19] reported that 4.15% PCE of Zn-doped SnO2 DSCs was nearly four times as that of pure SnO2 device. Furthermore, Shin’s group reported Sr-doped BaSnO2 DSCs [20]. Open-circuit voltage (Voc) of Sr-doped BaSnO2 DSCs increased from 0
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