Abstract
The novel donor building-block - 9-(p-tolyl)-2,3,4,4a,9,9a-hexahydro-1H-carbazole was designed and employed in the synthesis of dye-sensitized solar cell (DSSCs). An effective, high-yielding synthesis of 4,6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9-(p-tolyl)-1,2,3,4,4a,9a-hexahydrocarbazole from 1,2,3,4,4a,9a-hexahydrocarbazole was realized. Three new metal-free organic sensitizers, containing the new donor building block were prepared by a stepwise approach from 4,7-dibromobenzo[c][1,2,5]chacogenadiazoles. A 2,1,3-Benzothiadiazole dye containing hexahydrocarbazole donor, thiophene as π-spacer and cyanoacrylate as anchoring electron acceptor showed photovoltaic properties higher than the well-known WS-2 sensitizer with PCE = 5.86 %. Although benzoxa- and –selenadiazole dyes have a bathochromic shift (24−30 nm) in the UV–vis spectra, and smaller energy gap Eg (about 0.1 eV), they have lower photovoltaic parameters, including PCE of 1.5–2.3 %. Introducing a new donor 9-(p-tolyl)-2,3,4,4a,9,9a-hexahydro-1H-carbazole into the construction of the DSSCs has broadened possibilities for the optimization of their photovoltaic properties.
Highlights
In the last couple of decades, dye-sensitized solar cells (DSSCs) have attracted worldwide research attention due to their potential for low cost production, easy fabrication and relatively high power conversion efficiency [1,2,3]
3.1 Synthesis and characterization The molecular structures of the dyes, containing the novel donor building-block - 9-(p-tolyl)2,3,4,4a,9,9a-hexahydro-1H-carbazole, are shown in Scheme 1. 4,6-(4,4,5,5-Tetramethyl1,3,2-dioxaborolan-2-yl)-9-(p-tolyl)-1,2,3,4,4a,9a-hexahydrocarbazole 4 was prepared in four steps from 1,2,3,4,4a,9a-hexahydrocarbazole 1 Scheme 2
Three novel D-A-π-A metal-free organic sensitizers were obtained using this donor. 2,1,3-Benzothiadiazole sensitizer MAX114 based on 9-(p-tolyl)-2,3,4,4a,9,9a-hexahydro-1H-carbazole showed higher PCE by comparison to the well-known 4-(p-tolyl)-1,2,3,3a,4,8bhexahydrocyclopenta[b]indolyl building block, which is varied from extensively investigated 4-(p-tolyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indole by one excessive CH2 group in indoline cycle
Summary
In the last couple of decades, dye-sensitized solar cells (DSSCs) have attracted worldwide research attention due to their potential for low cost production, easy fabrication and relatively high power conversion efficiency [1,2,3]. Among other components of DSSCs, the dye sensitizer is responsible for harvesting sunlight, initiating charge transfer, and injecting electrons into the photoanode. Most typical organic dyes are designed with a donor-π-bridge-acceptor (D-π-A) configuration due to easy synthesis and efficient intramolecular charge transfer (ICT) properties [12,13,14,15]. The electronic interaction between donor (D) and acceptor (A) results in strong charge-transfer absorption bands that harvest sunlight for photon-to-electron conversion. Compared to D–π–A dyes, the properties of D–A–π–A dyes can be readily adjusted by incorporation of an auxiliary acceptor between the donor and π-bridge, which broadens the absorption and enhances efficient ICT for high performance DSSCs [19]. Various other molecular engineering methods to improve the light harvesting efficiency of organic dyes involve an increase in the electronic richness of the donor moieties [28]. Triarylamine, indoline, tetrahydroquinoline, phenothiazine, phenoxazine are routinely used as donors [30]. 4-(p-
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