Comparison between Benzothiadizole-Thiophene- and Benzothiadizole-Furan-Based D-A-π-A Dyes Applied in Dye-Sensitized Solar Cells: Experimental and Theoretical Insights.

Walid Sharmoukh,Jiayan Cong,Basant A Ali,Nageh K Allam,Lars Kloo

doi:10.1021/acsomega.0c02060

Abstract

Three novel donor–acceptor−π–acceptor-type compounds (WS5, WS6, and WS7) were synthesized and investigated in dye-sensitized solar cells (DSSCs) exploring the effect of conjugated linkers on device performance. The new dyes showed strong light-harvesting ability in the visible region with relatively high molar absorption coefficients (>21 800 M–1 cm–1). This can be attributed to their intrinsic charge transfer (CT) from the arylamine to the acceptor group. Density functional theory (DFT) calculations revealed a favorable lowest unoccupied molecular orbital (LUMO) energy level, allowing efficient injection into the semiconductor conduction band after excitation. Upon application in DSSC devices, the WS5 dye containing 4,7-di(furan-2-yl)benzo[c][1,2,5]thiadiazole as conjugated linker mediated the highest device power conversion efficiency (PCE) amounting to 5.5%. This is higher than that of the WS6-containing dye based on the 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole linker (3.5%) and the WS7 dye based on the 4-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole linker (4.3%) under AM 1.5 G illumination. The present results show furan-based dye linker systems to have a significant potential for improving DSSC efficiencies.

Highlights

Dye-sensitized solar cells (DSSCs) have attracted considerable attention due to their potential low cost and ease of fabrication.[1]
Photosensitizers based on porphyrins,[2] ruthenium complexes,[3−7] and metal-free molecular systems have been synthesized and used in DSSC devices.[8−13] power conversion efficiencies above 11% have been reported employing ruthenium-based sensitizers,[4,14,15] restricted access and ecological issues linked to ruthenium make it important to search for alternative dyes
Furan, thiophene’s oxygen analogue, which normally displays a high oxidation potential, is expected to increase the performance when applied in organic dyes for DSSCs.[23]

Summary

Introduction

Dye-sensitized solar cells (DSSCs) have attracted considerable attention due to their potential low cost and ease of fabrication.[1]. Much effort has been dedicated to overcome this bottleneck.[17−20] In particular, thiophene or thiophene-based heterocycles have been employed as the πconnecting linker in organic dyes, for instance, carbazole− oligothiophene,[21] coumarin−thiophene,[22] and benzothiadizole−thiophene.[12] Such organic dyes show good matching of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) mainly located on the thiophene moieties In this perspective, furan, thiophene’s oxygen analogue, which normally displays a high oxidation potential, is expected to increase the performance when applied in organic dyes for DSSCs.[23] The furan-based units are expected to bring better stability to the organic dyes synthesized

Methods

Results

Conclusion