D-A-π-A Motif Quinoxaline-Based Sensitizers with High Molar Extinction Coefficient for Quasi-Solid-State Dye-Sensitized Solar Cells.

Yu Wang,Tianyue Li,Zhiwei Zheng,Wenjun Wu,Jianli Hua,He Tian,Neil Robertson,Huaide Xiang,Wei-Hong Zhu

doi:10.1021/acsami.6b11152

Abstract

To meet the requirement of high molar extinction coefficient, broad absorption spectrum, and photo/thermal stability for sensitizers of quasi-solid-state dye-sensitized solar cells (Qs-DSSCs) with reduced film thickness, a novel D-A-π-A configuration organic sensitizer IQ22 was specifically designed, in which the conjugation bridge of cyclopentadithiophene (CPDT) unit was incorporated to widen the light response and enhance molar coefficients for increasing the short-circuit current density (JSC), and the octane chain on CPDT was targeted for suppressing the charge recombination and improving the open-circuit voltage (VOC). As a result, the Qs-DSSC based on IQ22 exhibits very promising conversion efficiency as high as 8.76%, with a JSC of 18.19 mA cm-2, a VOC of 715 mV, and a fill factor (FF) of 0.67 under AM 1.5 illumination (100 mW cm-2), standing out in the Qs-DSSCs utilizing metal-free organic sensitizers.

Highlights

The main practical limitations for the evolution of Qs-dye-sensitized solar cells (DSSCs) are lower power conversion efficiency (PCE) arising from low electrolyte ion diffusion rates and the resulting serious electronic recombination. 11-15 In this regard, quasi-solid state dye-sensitized solar cell (Qs-DSSC) always need thin TiO2 electrode, and an ideal sensitizer should exhibit strong light-harvesting capability
MPV-I was successfully exploited for fabricating Qs-DSSCs utilizing IQ22 and IQ4 as sensitizers, achieving high conversion efficiencies of 8.76% and 8.30% under 100 mW cm-2 illumination, respectively, which is an exhilarating PCE for Qs-DSSCs based on metal-free organic sensitizers
In order to quantify any bottleneck limiting the efficiency for Qs-DSSCs, we first performed conductivity (σ) measurements of gel and volatile electrolytes (See experimental section) with electrochemical impedance spectroscopy

Summary

Introduction

The main practical limitations for the evolution of Qs-DSSCs are lower power conversion efficiency (PCE) arising from low electrolyte ion diffusion rates and the resulting serious electronic recombination. 11-15 In this regard, Qs-DSSCs always need thin TiO2 electrode, and an ideal sensitizer should exhibit strong light-harvesting capability. The desirable sensitizer with high molar extinction coefficient and broaden light response region is very critical to the thinner TiO2 electrode-based Qs-DSSCs, in which the electronic recombination can be distinctly repressed, and the intramolecular charge transfer (ICT) can be optimized. MPV-I was successfully exploited for fabricating Qs-DSSCs utilizing IQ22 and IQ4 as sensitizers, achieving high conversion efficiencies of 8.76% and 8.30% under 100 mW cm-2 illumination, respectively, which is an exhilarating PCE for Qs-DSSCs based on metal-free organic sensitizers. These devices showed excellent stability, almost maintaining the initial conversion efficiency even after 1000 h

Methods

Results

Conclusion