Simple 3,6‐disubstituted Carbazoles as Potential Hole Transport Materials: Photophysical, Electrochemical and Theoretical Studies

Abstract

Developing effective and low‐cost organic hole‐transporting materials (HTMs) is crucial for the construction of high‐performance perovskite solar cells (PSCs) and to promote their production in commercial ventures. In this context, we herein report the molecular design, synthesis and characterization of two novel D‐A‐D‐A‐D architectured 9‐(2‐ethylhexyl)‐9H‐carbazoles, connecting the mono/dimethoxyphenyl substituted cyanovinylene sidearms symmetrically at 3rd and 6th positions of the carbazole heterocycle (CZ1‐2), as potential hole‐transporting materials (HTMs). The current work highlights their structural, photophysical, thermal, electrochemical and theoretical investigations, including their structure‐property correlation studies. Evidently, the optical studies showcased their excellent fluorescence ability due to their push–pull natured structure with extended π‐conjugation. Further, in‐depth solvatochromic studies demonstrated their intramolecular charge‐transfer (ICT)‐dominated optoelectronic behavior, supported by various correlation studies. Also, the optical results revealed that CZ1 and CZ2 display λabs and λemi in the order of 410–430 nm and 530–560 nm, respectively, with a bandgap in the range of 2.5–2.6 eV. Finally, their quantum chemical simulations have provided an insight into the predictions of their structural, molecular, electronic and optical parameters. Conclusively, the study furnishes a deeper understanding of the intricacies involved in the structural modification of carbazole‐based HTMs for achieving better performance.

Simple carbazole derivatives with mono/dimethoxyphenylacrylonitrile substituents as hole‐transporting materials: Performance studies in hybrid perovskite solar cells

“…The newly designed 9‐(2‐ethylhexyl)‐9 H ‐carbazole‐based organic materials CZ 1‐2 connecting the mono/dimethoxyphenyl substituted cyanovinylene side arms symmetrically at 3‐ and 6‐positions of the carbazole core, were synthesized using standard synthetic protocols as described in our previous paper. [ 25 ] New PSCs were fabricated employing CZ 1‐2 and Spiro‐OMeTAD as HTMs adopting the procedure as described below and their current‐voltage measurements were performed under simulated Air Mass 1.5 global illumination. Also, their photovoltaic spectral response measurements were made.…”

“…Scheme outlines the synthetic methods followed for CZ 1‐2 . In continuation of our previous work [ 25 ] , in this present study, we investigated comprehensively the device performance of these entities as well as well‐known Spiro‐OMeTAD as effective HTMs in new PSCs along with their in‐depth optical, electrochemical, thermal, and theoretical studies, to correlate the above‐mentioned properties with their structures.…”

Carbazole based organic dyes as effective photosensitizers: A comprehensive analysis of their structure‐property relationships

“…[ 17–26 ] Among the aforementioned systems, the heteroaromatic carbazole moiety is considered to be one of the most widely used electron donors in the design of the photosensitizers, mainly due to the fact that it has very good hole carrying ability with wide energy bandgap and allows facile substitution for hydrogen at different positions along with decent thermal and photochemical stability. [ 27–29 ] Further, the benzene and its analogs are used efficiently as the π‐spacer in the molecular engineering of the dyes due to their tunable spectroscopic and electrochemical behaviors, good charge transporting ability and increased overall stability and rigidity in the resulting dyes. [ 30 ] Further, the cyanoacetic acid and carboxyl groups have been reported to be effective electron acceptor/anchoring units for the design of new D‐π‐A type sensitizers and such dyes have been shown to display superior power conversion efficiency ( PCE ).…”

“…[17][18][19][20][21][22][23][24][25][26] Among the aforementioned systems, the heteroaromatic carbazole moiety is considered to be one of the most widely used electron donors in the design of the photosensitizers, mainly due to the fact that it has very good hole carrying ability with wide energy bandgap and allows facile substitution for hydrogen at different positions along with decent thermal and photochemical stability. [27][28][29] Further, the benzene and its analogs are used efficiently as the π-spacer in the molecular engineering of the dyes…”

Improving the Performance of Carbon-Based Perovskite Solar Modules (70 cm2) by Incorporating Cesium Halide in Mesoporous TiO2

“…The conventional PSC architecture consists of a transparent electrode TiO 2 as an electron transport layer (ETL), perovskite as a light harvester, Spiro-OMeTAD or PEDOT:PSS as the hole transport material (HTM), and the back electrode Au/Ag. , Although this architecture leads to the highest PCEs, the problem of instability of the organic HTM as well as perovskite in the presence of moisture in ambient air challenges the long-term use of the device, creating many hurdles for commercialization . Also, organic HTMs are expensive, increasing cost constraints for their production .…”