ORIGINAL PAPER Formulation of water to ethanol ratio as extraction solvents of Ixora coccinea and Bougainvillea glabra and their effect on dye aggregation in relation to DSSC performance Dk Nur Fhatihah Pg Damit 1 & Kalpana Galappaththi 2 & Andery Lim 1,2 & Mohammad Iskandar Petra 3 & Piyasiri Ekanayake 1,2 Received: 24 August 2015 /Revised: 29 September 2016 /Accepted: 8 October 2016 # Springer-Verlag Berlin Heidelberg 2016 Abstract Natural dye sensitizers from Ixora coccinea (anthocyanin) and Bougainvillea glabra (betalain) flowers were prepared in five different ratios of ethanol to water (0, 30, 50, 70, and 90 % ethanol), and the effect of dye aggrega- tion toward dye sensitized solar cell (DSSC) performance was evaluated. As the concentration of ethanol increases, the ten- dency of dye molecules to aggregate increased in Ixora dye extracts while no definite trend was observed in Bougainvillea dye extracts. The best DSSC performances of Ixora and Bougainvillea dyes exhibited by extracts in 70 % ethanol and 0 % ethanol are 0.58 ± 0.02 and 0.25 ± 0.02 %, respec- tively. Both high conversion efficiencies were ascribed to high electron density and low charge transfer resistance. From this study, it was revealed that the performances of DSSC could be affected by the formulation of dye aggregation on the TiO 2 surface. Keywords Anthocyanins . Betalains . Aggregation . Natural dye-sensitized solar cells Introduction Advancement in renewable energy research has been geared to the utilization of energy from the Sun as it is among the possible sources of infinite and clean energy in the future [1]. Solar technology has come a long way in terms of research, and the main motivation is to produce higher efficiency with cost-effective cells. With the ongoing increase in the world’ s population, the use of renewable energy technologies have been seen to increase more gradually in order to meet the demand for energy. This includes the third photovoltaic gen- eration, dye-sensitized solar cells (DSSCs), which were first reported by Brian O’Regan and Michael Grätzel (1991) and is currently emerging with a promising potential source of clean energy. DSSC has been considered as favorable alternatives to Si-based solar cells in the last two decades [2]. DSSC provides simple and low-cost materials for fabrica- tion as well as good portability [3, 4]. The mechanism is based on the sensitization of adsorbed dye on wide band gap n-type semiconductor [5]. The adsorption properties and the anchor- age of the dye onto the TiO 2 layer are very essential factors to DSSC performance [6] hence making sensitizers to be the key element in DSSC. Highest conversion efficiency of 12.8 % was achieved when using ruthenium (II) complexes as the dye sensitizers [7]. However, due to the presence of heavy metals that pose negative threats to the environment, natural dyes have become the viable options for their low cost and envi- ronmentally friendly properties [ 8 – 10 ]. To date, the * Piyasiri Ekanayake piyasiri.ekanayake@ubd.edu.bn Dk Nur Fhatihah Pg Damit dk.fatihah@gmail.com Kalpana Galappaththi kgalappaththi@yahoo.com Andery Lim anderylim@hotmail.com Mohammad Iskandar Petra iskandar.petra@ubd.edu.bn 1 Centre for Advanced Material and Energy Sciences, Universiti Brunei Darussalam, Jalan Tungku Link, Negara BE1410, Brunei Darussalam 2 Physical and Geological Sciences Programme, Universiti Brunei Darussalam, Jalan Tungku Link, Negara BE1410, Brunei Darussalam 3 Faculty of Integrated Technology, Universiti Brunei Darussalam, Jalan Tungku Link, Negara BE1410, Brunei Darussalam Ionics DOI 10.1007/s11581-016-1859-y