Panchromatic Ru(ii) sensitizers bearing single thiocyanate for high efficiency dye sensitized solar cells

Abstract

We report on a new series of Ru(II) sensitizers PRT-21–PRT-24 suitable for high performance dye sensitized solar cells (DSCs). Their molecular design consists of a tridentate anchor, a bidentate pyrazolate ancillary and a single thiocyanate. On this architecture, we examined two types of anchor, incorporating the traditional 4,4′4′′-tricarboxy-2,2′:6′,2′′-terpyridine (i.e. tctpy) and newly evaluated 4,4′-dicarboxy-6-quinolin-8-yl-2,2′-bipyridine (i.e. Qbpy). This modification, along with the synergistic incorporation of either 5-hexylthien-2-yl or 5-(hexylthio)thien-2-yl substituent at the 4-position of the pyridyl pyrazolate chelate for enhancing the optical response, leads to the achievement of DSC with a prominent J_SC of 20.4 mA cm⁻² and V_OC = 740 mV, and thus a high photon conversion efficiency of 11.16% using PRT-22. Comprehensive charge extraction, transient photovoltage and transient absorption measurements have been carried out to gain an insight into the fundamental mechanism of these new dyes and the associated device properties. These panchromatic Ru(II) sensitizers offer better product yields, higher stability and lower synthetic costs compared to that of black dye (N749), adding another dimension for better sensitizers en route to high performance DSCs.