Contents lists available at ScienceDirect Dyes and Pigments journal homepage: www.elsevier.com/locate/dyepig Blue-colored dyes featuring a diketopyrrolopyrrole spacer for translucent dye-sensitized solar cells Dong-suk Lim a,1 , Kyungah Choi b,1 , Dini Hayati a , Da-Heon Park a , Alvien Ghifari a , Kang Min Lee a , Yohan Ko c , Yongseok Jun c , Hyeon-Jeong Suk b,∗∗ , Jongin Hong a,∗ a Department of Chemistry, Chung-Ang University, 84 Heukseok-ro, Dongjak-gu, Seoul, 06974, Republic of Korea b Department of Industrial Design, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea c Department of Materials Chemistry & Engineering, 120 Neungdong-ro, Gwangjin-gu, Konkuk University, Seoul, 05029, Republic of Korea ARTICLEINFO Keywords: Dye-sensitized solar cells Diketpyrrolopyrrole Blue Density functional theory ABSTRACT We report the facile synthesis of blue-colored dyes featuring a diketopyrrolopyrrole (DPP) spacer with di- methylamine and bis(4-dibuotxylphenyl)-phenyl-amine as donor residues (CSD-08 and CSD-09), their spec- troscopic, electrochemical and colorifc properties, and their application to translucent dye-sensitized solar cells (DSSCs). In the DSSCs fabricated with 5 μm-thick TiO 2 photoanodes, CSD-08 and CSD-09 yield power-conver- sion-efciencies of 3.43% and 3.62%, respectively, under simulated one sun illumination. 1. Introduction The prosperity of human society mainly relies on fnding clean and renewable energy solutions. Solar is a clean and inexhaustible energy resource on the Earth, and thus the efcient use of solar energy has been considered as the most promising way to meet an everlasting global demand for energy. Recently, dye-sensitized solar cells (DSSCs) have attracted signifcant attention as environmentally friendly pho- tovoltaic cells instead of commercialized crystalline and thin-flm Si solar cells [1–4]. In public sectors, the DSSCs hold particular promise on fat and curved building skins for building-integrated photovoltaics (BIPV) because of their transparency and aesthetic value. To date, nu- merous eforts on device physics, material innovation and commercia- lization have been made to achieve high performance and long-term fdelity [3–9]. In particular, the photosensitizer is one of the critical components for both the power conversion efciency and the stability of the cells. Polypyridyl and porphyrin complexes of metals are typi- cally used for photosensitization in high-efciency DSSCs exhibiting power-conversion-efciency (η) higher than 11% under Air Mass 1.5 Global (AM 1.5 G) illumination [10,11]. Recently, metal-free organic dyes based on a typical donor-π conjugation spacer-acceptor (D-π-A) confguration have received intense interest because of high molar ex- tinction coefcients, bespoke structural modifcation through rich synthetic protocols and low-cost production [12–16]. Hitherto, many reddish dyes with strong absorbance below 600 nm have been suc- cessfully designed and synthesized for DSSCs. Unfortunately, they cannot efciently harvest the incident photons in the red and near-in- frared (NIR) range, and thus blue-colored dyes, as well as NIR absorbing dyes, should be developed for translucent solar aesthetics. Besides, when concerned with the visual appeal of a building's exterior, the color should ft the architectural design. Recently, a D-π-A′-π-A concept has been proposed to design novel organic sensitizers and the additional subordinate A′ unit can work as an “electron trap” to promote charge separation and electron migration in the structure [17]. Among several electron-withdrawing units, diketopyrrolopyrrole (DPP) is strongly electron-withdrawing because of the presence of two lactams and thus exhibits the electron-defcient character. Recently, organic molecules containing the DPP core have been exploited as blue-colored dyes [18–20] and other functional materials [21–25]. In this study, we re- port a facile synthesis of two DPP-based blue dyes (CSD-08 and CSD- 09, Scheme 1) with diferent donor groups, which can be conveniently prepared in two steps. Importantly, we adopt the acetylene group providing a planar linker moiety in D-π-A-π-A structure as a handle for further synthetic manipulation [15–17,26]. We also investigate the colorifc properties of the blue dyes and thus they enhance the aesthetic values of the DSSCs. https://doi.org/10.1016/j.dyepig.2019.107840 Received 3 March 2019; Received in revised form 24 August 2019; Accepted 25 August 2019 ∗ Corresponding author. ∗∗ Corresponding author. E-mail addresses: color@kaist.ac.kr (H.-J. Suk), hongj@cau.ac.kr (J. Hong). 1 Equal contribution to this article. Dyes and Pigments 173 (2020) 107840 Available online 28 September 2019 0143-7208/ © 2019 Published by Elsevier Ltd. T