Significant Influence of a Single Atom Change in Auxiliary Acceptor on Photovoltaic Properties of Porphyrin-Based Dye-Sensitized Solar Cells.

Haoran Zhou,Jung-Min Ji,Min Kim,Hwan Kim

doi:10.3390/nano8121030

Abstract

The rational design of porphyrin sensitizers is always crucial for dye-sensitized solar cells (DSSCs), since the change of only a single atom can have a significant influence on the photovoltaic performance. We incorporated the pyridothiadiazole group, as a stronger electron-withdrawing group, into the commonly well-established skeleton of D-porphyrin-triple bond-acceptor sensitizers by a single atom change for a well-known strong electron-withdrawing benzothiadiazole (BTD) unit as an auxiliary acceptor. The impact of the pyridothiadiazole group on the optical; electrochemical; and photovoltaic properties of D–π–A porphyrin sensitizers was investigated with comparison for a benzothiadiazole-substituted SGT-020 porphyrin. The pyridothiadiazole-substituted SGT-024 porphyrin dye was red-shifted so that the absorption range might be expected to achieve higher light harvest efficiency (LHE) than the SGT-020 porphyrin. However, all the devices were fabricated by utilizing SGT-020 and SGT-024, evaluated and found to achieve a cell efficiency of 10.3% for SGT-020-based DSSC but 4.2% for SGT-024-based DSSC under standard global AM 1.5G solar light conditions. The main reason is the lower charge collection efficiency of SGT-024-based DSSC than SGT-020-based DSSC, which can be attributed to the tilted dye adsorption mode on the TiO2 photoanode. This may allow for faster charge recombination, which eventually leads to lower Jsc, Voc and power conversion efficiency (PCE).

Highlights

A huge amount of work has recently concentrated on third-generation solar cell technology development with low cost as emerging photovoltaics, such as dye-sensitized solar cells (DSSCs) [1,2], organic photovoltaics (OPVs) [3,4,5], perovskite solar cells (PSCs) [6,7,8], etc
The results revealed that the reduction potential values are much more negative than the conducting band (CB) of TiO2 and the oxidation potential values are much more positive than the Co(bpy)32+/3+ redox couple (0.56 V vs. NHE), indicating that all of the electron transfer processes for two porphyrin sensitizers should occur efficiently due to the sufficient driving force
The results revealed that the reduction potential values are much more negative than the conducting band (CB) of TiO2 and the oxidation potential values are much more positive than the Co(bpy)32+/3+ redox couple (0.56 V vs. NHE), indicating that all of the electron transfer processes for two porphyrin sensitizers should occur efficiently due to the sufficient driFviigngurfoerc1e..Absorption spectra and emission spectra of SGT-020 and SGT-024 in THF

Summary

Introduction

A huge amount of work has recently concentrated on third-generation solar cell technology development with low cost as emerging photovoltaics, such as dye-sensitized solar cells (DSSCs) [1,2], organic photovoltaics (OPVs) [3,4,5], perovskite solar cells (PSCs) [6,7,8], etc. Among the various solar technologies, DSSCs have garnered considerable attention due to the simple fabrication process, low cost, low toxicity, and high PCE under ambient lighting conditions [9,10]. In 1991 Grätzel and O’Regan first introduced mesoporous TiO2 nanocrystal layers into the DSSC system [11]. This led to a substantial improvement in photoelectric transformation efficiency. State-of-the-art DSSCs have achieved PCEs approaching >11.9% for ruthenium complexes [15], >14% for metal-free D–π–A structural organic sensitizers [16], and 14.64% for D–π–A structural organic sensitizer-based tandem DSSCs under standard (1.5) illumination [13]. In comparison with ruthenium sensitizers [17,18] and metal-free sensitizers [19,20], D–π–A structural porphyrin sensitizers [21,22,23] have been attractive

Methods

Findings

Conclusion