Solution Processable Fluorenyl Hexa‐peri‐hexabenzocoronenes in Organic Field‐Effect Transistors and Solar Cells

Abstract

The organization of organic semiconductor molecules in the active layer of organic electronic devices has important consequences to overall device performance. This is due to the fact that molecular organization directly affects charge carrier mobility of the material. Organic field‐effect transistor (OFET) performance is driven by high charge carrier mobility while bulk heterojunction (BHJ) solar cells require balanced hole and electron transport. By investigating the properties and device performance of three structural variations of the fluorenyl hexa‐peri‐hexabenzocoronene (FHBC) material, the importance of molecular organization to device performance was highlighted. It is clear from 1H NMR and 2D wide‐angle X‐ray scattering (2D WAXS) experiments that the sterically demanding 9,9‐dioctylfluorene groups are preventing π–π intermolecular contact in the hexakis‐substituted FHBC 4. For bis‐substituted FHBC compounds 5 and 6, π–π intermolecular contact was observed in solution and hexagonal columnar ordering was observed in solid state. Furthermore, in atomic force microscopy (AFM) experiments, nanoscale phase separation was observed in thin films of FHBC and [6,6]‐phenyl‐C61‐butyric acid methyl ester (PC61BM) blends. The differences in molecular and bulk structural features were found to correlate with OFET and BHJ solar cell performance. Poor OFET and BHJ solar cells devices were obtained for FHBC compound 4 while compounds 5 and 6 gave excellent devices. In particular, the field‐effect mobility of FHBC 6, deposited by spin‐casting, reached 2.8 × 10−3 cm2 V−1 s and a power conversion efficiency of 1.5% was recorded for the BHJ solar cell containing FHBC 6 and PC61BM.

Optimized solution-processed merocyanine:PCBM organic bulk heterojunction solar cell

“…Comparable values were also reported for pigment-based solar cells using acene, [13][14][15] squaraine, 16,17 boron dipyrromethene, 18 and merocyanine dyes. 19 Recently, outstanding PCE values of up to 4.4% have been reported by Tamayo et al 20 and Walker et al 21 for molecules composed of two subunits, a dye and a semiconductor part.…”

“…7 Recently, the first BHJ solar cells that are based entirely on small conjugated molecules (i.e., PCBM as electron acceptor and various electron donor components) have been published, indicating the increasing interest in this emerging research field. [8][9][10][11][12][13][14][15][16][17][18][19][20] With dendrimers or oligomers based on typical organic semiconductors derived from oligothiophenes, PCE values up to 2.5% could be achieved.…”

Synthesis and thermotropic behavior of side chain polysiloxane bearing triphenylene moiety

“…Again, the most Figure 1. Synthesis of unsymmetric triphenylene and the relevant discotic side chain polysiloxane difficult part of the process was purification of the ester (4). The attachment of the side triphenylene groups to the polysiloxane was performed in typical hydrosilylation conditions (Figure 1) in toluene using Karstedt's catalyst at 60-80°C.…”

“…The DSC heating scan (Figure 2a) reveals a phase transition temperature from the crystalline (Cr) to the liquid crystalline (LC) phase at 68°C for (4) and 67°C for (6). The temperature difference, which accompanies this transition for (4) and (6) is %T = 1°C and a corresponding small change in enthalpy is observed (%H = 0.6 J/g). Transition to the isotropic phase (Iso) occurs at the temperature of 99°C and is identical for both monomer (4) and polymer (6).…”

“…They have been extensively studied as a result of their electro-optical and semiconducting properties as well as expected applications in organic field effect transistor devices (OFET) and solar cells [4][5][6]. They can undergo an easy macroscopic alignment and can be processed in a simple way [7][8][9].…”