Metal-Free Tetrathienoacene Sensitizers for High-Performance Dye-Sensitized Solar Cells

Abstract

A new series of metal-free organic chromophores (TPA-TTAR-A (1), TPA-T-TTAR-A (2), TPA-TTAR-T-A (3), and TPA-T-TTAR-T-A (4)) are synthesized for application in dye-sensitized solar cells (DSSC) based on a donor-π-bridge-acceptor (D-π-A) design. Here a simple triphenylamine (TPA) moiety serves as the electron donor, a cyanoacrylic acid as the electron acceptor and anchoring group, and a novel tetrathienoacene (TTA) as the π-bridge unit. Because of the extensively conjugated TTA π-bridge, these dyes exhibit high extinction coefficients (4.5-5.2 × 10(4) M(-1) cm(-1)). By strategically inserting a thiophene spacer on the donor or acceptor side of the molecules, the electronic structures of these TTA-based dyes can be readily tuned. Furthermore, addition of a thiophene spacer has a significant influence on the dye orientation and self-assembly modality on TiO2 surfaces. The insertion of a thiophene between the π-bridge and the cyanoacrylic acid anchoring group in TPA-TTAR-T-A (dye 3) promotes more vertical dye orientation and denser packing on TiO2 (molecular footprint = 79 Å(2)), thus enabling optimal dye loading. Using dye 3, a DSSC power conversion efficiency (PCE) of 10.1% with Voc = 0.833 V, Jsc = 16.5 mA/cm(2), and FF = 70.0% is achieved, among the highest reported to date for metal-free organic DSSC sensitizers using an I(-)/I3(-) redox shuttle. Photophysical measurements on dye-grafted TiO2 films reveal that the additional thiophene unit in dye 3 enhances the electron injection efficiency, in agreement with the high quantum efficiency.

An Experimental and Theoretical Investigation of the Electronic Structures and Photoelectrical Properties of Ethyl Red and Carminic Acid for DSSC Application

“…This has limited the application of metal-bearing dyes for DSSCs [7]. Recently, much research has focused on the study of metal-free organic DSSCs due to the rich raw materials, flexible molecular design, easy synthesis, low cost [8,9,10,11,12,13,14], and organic optoelectronic materials [15,16]. It is worth noting that Yao and co-workers [11] synthesized a metal-free organic dye (C281), which showed over 80% external quantum efficiency in a broad spectral range from 480 to 735 nm, and a high PCE of 13.0% under irradiance of simulated AM 1.5G sunlight (100 mW·cm −2 ).…”

Organic dyes with a fused segment comprising benzotriazole and thieno[3,2-b]pyrrole entities as the conjugated spacer for high performance dye-sensitized solar cells

“…These sensitizers absorb broadly and intensely as the planarized π−spacer is helpful to the delocalization of π-electrons and electron transfer from the donor to the acceptor. 11,12 Reduction of reorganization energy during photoinduced charge transfer is also anticipated with the rigidified π−spacer. 13,14 Accordingly, these sensitizers have very promising cell performance, which rivals that of N719 based standard DSSC.…”

Molecular design of novel indacenodithiophene‐based organic dyes for efficient dye‐sensitized solar cells applications

“…Recently, by increasing the structural coplanarity, spacers with better π‐conjugation have been fused into the organic dyes to red‐shift optical spectrum and to yield panchromatic light harvesting . Metal‐free organic dyes with fused thiophene, anthracene, and dithieno[3,2‐b:2′,3′‐d]pyrrole have been reported with desirable power conversion efficiencies.…”