Effect of microfluidic electrolyte on the photovoltaic performance of ZnO-nanowire-based dye-sensitised solar cells

Abstract

ZnO-nanowire-based dye-sensitised solar cells (DSSCs) were prepared to investigate the effect of microfluidic electrolyte on the photovoltaic performance of solar cells. At first, long and well-aligned ZnO nanowires were synthesised on FTO substrate via the improved hydrothermal method. The structure and crystallinity properties of ZnO nanowires were characterised by using SEM, TEM and XRD. The photovoltaic characteristics of the assembled DSSCs were measured under various flowrates of microfluidic electrolyte. The results showed that variations of the microfluidic electrolyte had little effect on the fill factor of the cells. However, the photocurrent and photovoltage of the solar cells exhibited systematic changes with the decrease of microfluidic electrolyte: the short-circuited current of the DSSCs decreased while the open-circuit voltage increased. The phenomenon could remain in some extent after cessation of injecting the electrolyte within a short time. The possible influencing mechanism of the microfluidic electrolyte on the photovoltaic performance was discussed. DSSCs : dye-sensitised solar cells FF : fill factor J SC : short-circuited current PVA : poly (vinyl alcohol) TCO : transparent conductive oxide V OC : open-circuit voltageDye-sensitized solar cells (DSSCs) have the merit of high power conversion efficiency, excellent flexibility, lowcost, and ease-to-manufacture compared with traditional semiconductor solar cells, 1-4 and they have attracted numerous researchers' attention for decades. At present, the highest energy conversion efficiency of DSSCs is over 13%, and further increase of the efficiency is still possible. 5,6 In general, DSSCs comprise three parts: a dye-sensitised nanostructured semiconductor electrode, which is fabricated on transparent conductive oxide (TCO) substrate, a platinum counter electrode, and an electrolyte solution containing iodide ion/ tri-iodide ion redox couple. 7 During the past decades, remarkable efforts have been dedicated to developing novel photoelectrodes, 8,9 designing new light-trapping techniques, 10 new dyes 11 and redox couples 12 in order to improve the photovoltaic performance of DSSCs. Microfluidics is the science and technology of systems that process or manipulate small amount of fluids, using channels with dimensions of tens to hundreds of micrometers. 13 It offers a number of useful capabilities such as the ability to use very small quantities of samples and reagents, and to carry out separations and detections with high resolution and sensitivity, low cost, short times for analysis, and small footprints for the analytical devices. 14 The natural application scenario of microfluidics is in microbiology, 15 but it has been shown to have a multidisciplinary approach that make it promising in a wide range of research fields, including energy conversion. 16 Recently, A. Lamberti proposed the concept of microfluidic sealing, which was in favour of reaching higher photovoltaic efficiency compared to that of DSSCs assembled in the conventional way. 17 Ho...