The influence of alkyl chains on the performance of DSCs employing iron(II) N-heterocyclic carbene sensitizers.

Mariia Becker,Vanessa Wyss,Edwin C Constable,Catherine E Housecroft

doi:10.1039/d1dt03252f

Abstract

The photovoltaic performances of DSCs employing two new iron(ii) N-heterocyclic carbene (NHC) sensitizers are presented. The presence of n-butyl side chains had a significant impact on DSC performace. The improvement in DSC performance up to 0.93–0.95% was observed for a new heteroleptic sensitizer bearing one carboxylic acid anchoring group. The photovoltaic performance was remarkably affected by sensitization time and by a presence/absence of coadsorbent on the semiconductor surface. The highest photoconversion efficiencies (PCE) were achieved for DSCs sensitized over 17.5 hours without addition of coadsorbents. However, for a shorter dipping time of 4 hours, the presence of chenodeoxycholic acid improved the PCE from 0.46% (no coadsorbents) to 0.74%, respectively. The performance of DSCs based on a new homoleptic complex bearing two n-butyl side chains and a carboxylic acid anchor on each NHC-ligand was improved from 0.05 to 0.29% via changes in dye-bath concentration and sensitization time. The changes in the dye load on the semiconductor surface depending on the sensitization conditions were confirmed using solid-state UV-Vis spectroscopy and thermogravimetric analysis. Electrochemical impedance spectroscopy was used to gain information about the processes occurring at the different interfaces in the DSCs. The impedance response was strongly affected by the immersion time of the photoanodes in the dye-bath solutions. In the case of the homoleptic iron(ii) complex, a Gerischer impedance was observed after 17.5 hours immersion. Shorter dipping times resulted in a decrease in the resistance in the system. For the heteroleptic complex, values of the chemical capacitance and electron lifetime were affected by the immersion time. However, the diffusion length was independent of sensitization conditions.

Highlights

According to the Intergovernmental Panel on Climate Change (IPCC) that released its 6th Assessment Report on the Physical Science Basis for climate change on August 2021,1 the manmade contribution to global warming resulted in numerous extreme incidents including tropical cyclones, heavy precipitation, heatwaves and droughts
This is the result of fast deactivation from an metal-to-ligand charge transfer (MLCT) to metal-centred (MC) state.7a In 2013, the first iron(II) N-heterocyclic carbene (NHC) complex with an extended 3MLCT state lifetime of 9 ps was published by Wärnmark and co-workers, and DSCs sensitized with complex 1 (Fig. 1) gave 0.13% photoconversion efficiencies (PCE).7b This breakthrough resulted in optimization studies of DSCs sensitized with 1.8 In 2018, it was shown that the PCE could be improved from 0.13 to 0.57%
We present a study of DSCs based on new homoleptic and heteroleptic iron(II) NHC complexes 2 and 3, respectively (Fig. 2), with n-butyl functionalities, and investigate the optimization of the electrode sensitization process in terms of time, presence of coadsorbent and concentration of the dye-bath solution

Summary

Introduction

According to the Intergovernmental Panel on Climate Change (IPCC) that released its 6th Assessment Report on the Physical Science Basis for climate change on August 2021,1 the manmade contribution to global warming resulted in numerous extreme incidents including tropical cyclones, heavy precipitation, heatwaves and droughts. We present a study of DSCs based on new homoleptic and heteroleptic iron(II) NHC complexes 2 and 3, respectively (Fig. 2), with n-butyl functionalities, and investigate the optimization of the electrode sensitization process in terms of time, presence of coadsorbent and concentration of the dye-bath solution.

Results

Conclusion