Exploring the relevance of thiophene rings as bridge unit in acceptor‐bridge‐donor dyes on self‐aggregation and performance in DSSCs

Abstract

The possibility of dye charge recombination in DSSCs remains a challenge for the field. This consists of: (a) back-transfer from the TiO to the oxidized dye and (b) intermolecular electron transfer between dyes. The latter is attributed to dye aggregation due to dimeric conformations. This leads to poor electron injection which decreases the photocurrent conversion efficiency. Most organic sensitizers are characterized by an Acceptor-Bridge-Donor (A-Bridge-D) arrangement that is commonly employed to provide charge separation and, therefore, lowering the unwanted back-transfer. Here, we address the intermolecular electron transfer by studying the dimerization and photovoltaic performance of a group of A-Bridge-D structured dyes. Specifically, eight famous sulfur containing π-bridges were analyzed (A and D remained fixed). Through quantum mechanical and molecular dynamics approaches, it was found that the formation of weakly stabilized dimers is allowed. The dyes with covalently bonded and fused thiophene rings as Bridges, 6d and 7d as well as 8d with a fluorene, would present high aggregation and, therefore, high probability of recombination processes. Conversely, using TiO cluster and surface models, delineated the shortest bridges to improve the adsorption energy and the stability of the system. Finally, the elongation of the bridge up to 2 and 3 units and their photovoltaic parameters were studied. These results showed that all the sensitizers are able to provide similar photocurrent outcomes, regardless of whether the bridge is elongated. © 2017 Wiley Periodicals, Inc.

Bipodal dyes with bichromic triphenylamine architectures for use in dye-sensitized solar cell applications

“…Based on the physical data above, when considering the utility of these dyes for DSSC applications, the HOMO orbital resides at a favourable energy when considering the common electrolytes and regeneration dynamics. 31 In addition, each of these dyes possess LUMO orbitals situated on the acceptor units, and therefore injection should be kinetically favourable. When compared to benchmark L1, the blue shifted or weaker absorbing profiles of OA1, OA2 and OA3 may manifest in weaker device performance, but the addition of multiple redox active centres may increase the redox robustness of the dye, and could improve electron injection rates.…”

A comparison of methods for theoretical photochemistry: Applications, successes and challenges

“…An earlier study by Zarate et al 191 also studied dye-sensitized solar cell models, employing both B3LYP with added dispersion corrections and CAM-B3LYP. Here, CAM-B3LYP was employed to calculate the vertical excitation energy, and a comparison to values as calculated by the ωB97X-D, BHHLYP, M06-2 Â, M11, HISSbPBE, HSE06, M06, PBE, and TPSSh functionals was performed.…”

Exploration of 4-substituted thiophene-based azo dyes for dye-sensitized solar cells and non-linear optical materials: synthesis and an in silico approach

“…[32][33][34] Additionally, dyes with these spacers are expected to show efficient CT, which can be used in both linear and non-linear optics, with prospective uses in optical computing, optical signal processing, telecommunications, and additional applications as a bridge for DSSCs. 15,35 In this context, with a D-A system and thiophene as a p-conjugated bridge, Kim et al produced dyes based on phenothiazine (PTZ) and cyanoacrylic acid, which indicated that the thiophene bridge affects DSSC performance. 36 A few theoretical and experimental investigations have been published on azo dyes with low PCE DSSC applications.…”