Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc Full length article Highly interconnected porous TiO 2 -Ni-MOF composite aerogel photoanodes for high power conversion efficiency in quasi-solid dye-sensitized solar cells Velayutham Ramasubbu a , Poomani Ram Kumar a , Ebrahim M. Mothi a , K. Karuppasamy b , Hyun-Seok Kim b , T. Maiyalagan c , Xavier Sahaya Shajan a, ⁎ a Centre for Scientific and Applied Research (CSAR), PSN College of Engineering and Technology, Melathediyoor, Tirunelveli 627152, Tamil Nadu, India b Division of Electronics and Electrical Engineering, Dongguk University-Seoul, Seoul 04620, Republic of Korea c Electrochemical Energy Laboratory, Department of Chemistry, SRM Institute of Science and Technology, Kattankulathur 603203, India ARTICLE INFO Keywords: Titania aerogel Ni-MOF Photoanode Energy ABSTRACT Three-dimensional mesoporous TiO 2 -Ni-MOF composite aerogels were synthesized via sol–gel route and used as photoanode materials for quasi-solid dye-sensitized solar cell (QSDSC) applications. The assessment of their photovoltaic performance revealed an enhancement compared to pure aerogel-based QSDSCs; the maximum photo-conversion efficiency of the fabricated photoanode was 8.846% for 0.5% composite aerogel, which is ~30% higher than that of pure aerogel-based ones (6.805%). The achievement of other key factors required for efficiency enhancement such as increased photocurrent density, reduced charge-transfer resistance, and sup- pressed electron recombination was confirmed by photocurrent density–applied voltage curves and electro- chemical impedance measurements. The surface area of the composite aerogels ranged between 269 and 233 m 2 g -1 , which make them promising candidates for high-efficiency QSDSCs. 1. Introduction Clean energy is a significant prerequisite for the sustainability of the future generation and to overcome the adverse environmental effects of fossil fuel depletion [1,2]. Nature uses sunlight as an unpolluted and renewable energy source and, hence, the solar photovoltaic (PV) tech- nology appears very much dependable for our current and future en- ergy needs. However, the high cost of silicon PV panels has resulted in their underutilization and inaccessibility to the majority of the popu- lation [3–5]. Dye-sensitized solar cells (DSSCs), advanced and inspired by photosynthesis, are less expensive, easy to fabricate, and en- vironmentally safe, offering an excellent application potential; [6–8] their component architectures make the DSSC modules flexible and colorful, adding aesthetic value. However, high power conversion ef- ficiency (PCE) and long-term durability of the device are required for DSSCs operating with their full potential. The PCE is influenced by many factors, such as light harvesting, electron injection, regeneration, and recombination processes, while the device durability mainly suffers from liquid electrolyte leakage, evaporation, and poor stability [9,10]. Quasi-solid DSSCs (QSDSCs) developed from polymer gel electrolytes are promising in terms of long-term durability, but their cell efficiency is highly suppressed due to low conductivity and poor electrolyte penetration [11]; hence, QSDSCs with both enhanced device durability and higher power output are critical to develop. An important feature of the DSSC architecture is the interdependence among its components, such as semiconductors, dyes, and electrolytes, i.e., when one compo- nent is modified, the others will have to be optimized for achieving better performance. In this present investigation, we endeavored to develop a suitable semiconductor film for use in QSDSC. Although TiO 2 is the most common semiconductor material for DSSCs and has the advantages of low-cost, superior thermal and che- mical stability, and non-toxicity, its poor electron mobility is a major drawback [12]. Improving the electron transport pathway is a critical factor to enhance the final power output of a device. Currently, wide spread researches have devoted to enhance the properties of TiO 2 such as nano-architectural modifications, doping, and composite formation [13]. Especially, TiO 2 composites have shown great progress as efficient photoanodes in the recent years [13,14]. For example, carbon nano- tube–TiO 2 and Au–TiO 2 composites exhibited enhanced PCE of 9.0% and 10.1%, respectively, compared to that of pure TiO 2 (5.5%) [14,15]. However, most of such best performing composite materials are based on nanocarbon or Au/Ag nanoparticles, which increase the manu- facturing costs. In this context, we are interested in developing meta- l–organic frameworks (MOFs) as novel, cost-effective, and high https://doi.org/10.1016/j.apsusc.2019.143646 Received 16 February 2019; Received in revised form 2 June 2019; Accepted 10 August 2019 ⁎ Corresponding author. E-mail address: shajan89@psnresearch.ac.in (X.S. Shajan). Applied Surface Science 496 (2019) 143646 Available online 12 August 2019 0169-4332/ © 2019 Elsevier B.V. All rights reserved. T