Fluorenyl Hexa‐peri‐hexabenzocoronene‐Dendritic Oligothiophene Hybrid Materials: Synthesis, Photophysical Properties, Self‐Association Behaviour and Device Performance

Abstract

Apart from molecular properties, intermolecular forces play a vital role in defining the performance of organic electronic devices. This is particularly relevant in bulk heterojunction (BHJ) solar cells in which the arrangement of electron-donor and -acceptor materials into distinct crystalline phases of ideal size and distribution can lead to better power conversion efficiencies. In this study, a series of fluorenyl hexa-peri-hexabenzocoronenes (FHBC) decorated with thiophene dendrons (DOT) of variable size was obtained by using a convergent synthetic approach. With such variety of molecular sizes and shapes in hand, the objective of this study is to highlight the relationships between molecular properties, bulk properties and device performance. Correlations between π-π stacking ability and dendrimer generation were established from self-organisation studies in solution and solid state. The synergistic combination of molecular organisation at the nanoscale and photophysical characteristics derived from the FHBC and DOT moieties leads to a notable improvement of the photovoltaic performance.

Polycyclic aromatic hydrocarbons for organic photovoltaics

“…The photoluminescence (PL) spectrum of FHBC-thiophene hybrid compounds 23a-d are shown in Figure 1c. [12] Emission from the HBC core was observed for compounds 3, 23a and 23b starting at 465 nm. For compounds 23c and 23d, there is clear energy transfer from the HBC core to the thiophene dendron with only emission (530 and 560 nm) from the thiophene substituent observed (Figure 1c).…”

“…Further functionalization of FHBC compounds can also affect the way FHBC molecules aggregate in solution and in solid state. [9,[12][13][14] Figure 5 shows the 2D-WAXS patterns of FHBC-thiophene derivatives. Helical packing of FHBC-thiophene compound 23b was observed presumably as a result of the steric bulk of the thiophene substituent forcing the molecules to π−π stack in a staggered manner ( Figure 5).…”

“…[10] Upon further derivatization, the UV-vis absorption of FHBC derivatives can be broadened as illustrated by thiophene dendron-substituted FHBC compounds 23a-d ( Figure 1b). [12] However, the broadening of the spectrum is largely due to the absorption of the thiophene substituent rather than any extension in conjugation between the FHBC core and the functional group. The absorption of FHBC compounds are further broadened in solid state which is indicative of strong molecular aggregation ( Figure 1b).…”

“…[9,10,[12][13][14] A typical BHJ device structure is shown in Figure 7a. The transparent electrode is indium tin oxide (ITO) on glass.…”

“…[9][10][11] The fluorene unit not only imparts solubility on the HBC core but also enables facile extension. This new strategy has led to a range of hybrid compounds incorporating thiophene [12] and porphyrin [13] chromophores as well as electroactive fullerenes. [14] In this article, we will summarize our work on FHBC derivatives and discuss insights gained particularly for organic photovoltaic applications.…”