DOI: 10.1002/chem.201100211 Fluorenyl Hexa-peri-hexabenzocoronene-Dendritic Oligothiophene Hybrid Materials: Synthesis, Photophysical Properties, Self-Association Behaviour and Device Performance Wallace W. H. Wong,* [a] Chang-Qi Ma,* [b] Wojciech Pisula, [c] Alexey Mavrinskiy, [c] Xinliang Feng, [c] Helga Seyler, [a] David J. Jones, [a] Klaus Müllen, [c] Peter Bäuerle, [b] and Andrew B. Holmes [a] Introduction The design of molecules for application in organic electron- ics is a multi-parameter problem. The materials under con- sideration must have a combination of molecular and bulk properties suitable for the specific application. For bulk het- erojunction (BHJ) organic photovoltaics (OPV), the device performance is dependent on the light-harvesting capacity of the active material and its ability to efficiently transport charges to the electrodes after exciton generation and charge separation. [1] In the bulk heterojunction the electron and hole mobilities depend on the properties of the individ- ual electron acceptor and donor materials and the phase separation between the two active layer components. After exciton formation and migration to a donor-acceptor inter- face, charge separation occurs. Electrons in the active layer move through regions rich in electron-acceptor material, whereas holes migrate through the electron-donor-rich phase. With the exciton diffusion length in organic materials restricted to approximately 10 nm, the morphology of the active layer should consist of a network of interpenetrating acceptor and donor-rich phases with domain size ideally in the range of 10 to 20 nm. [2, 3] The crystallinity of the domains is also crucial to the overall charge mobility of the active layer. These two characteristics are common in both poly- mer and small-molecule-based BHJ solar cells. A well- known example is the combination of poly(3-hexylthio- phene) (P3HT) and [6,6]-phenyl-C 61 -butyric acid methyl ester (PC 61 BM). [1] The p–p interaction in the P3HT bulk material is essential for driving both the crystallinity of the P3HT domain and the phase separation from the PC 61 BM domain. In this study, hexa-peri-hexabenzocoronene (HBC) with a family of thiophene dendrons attached to its periph- ery was investigated as a self-organising electron-donor component in combination with fullerenes for BHJ solar cells. HBC is a planar aromatic molecule consisting of thirteen fused six-membered rings. [4, 5] It belongs to a family of poly- cyclic aromatic hydrocarbons consisting of flat disc-like Abstract: Apart from molecular prop- erties, intermolecular forces play a vital role in defining the performance of or- ganic electronic devices. This is particu- larly relevant in bulk heterojunction (BHJ) solar cells in which the arrange- ment of electron-donor and -acceptor materials into distinct crystalline phases of ideal size and distribution can lead to better power conversion ef- ficiencies. In this study, a series of fluo- renyl hexa-peri-hexabenzocoronenes (FHBC) decorated with thiophene den- drons (DOT) of variable size was ob- tained by using a convergent synthetic approach. With such variety of molecu- lar sizes and shapes in hand, the objec- tive of this study is to highlight the re- lationships between molecular proper- ties, bulk properties and device perfor- mance. Correlations between p–p stacking ability and dendrimer genera- tion were established from self-organi- sation studies in solution and solid state. The synergistic combination of molecular organisation at the nano- scale and photophysical characteristics derived from the FHBC and DOT moi- eties leads to a notable improvement of the photovoltaic performance. Keywords: aromatic hydrocarbons · dendrimers · organic solar cells · self-assembly · thin films [a] Dr. W. W. H. Wong, Dr. H. Seyler, Dr. D. J. Jones, Prof. A. B. Holmes School of Chemistry University of Melbourne Bio21 Institute 30 Flemington Road Parkville, Victoria 3010 (Australia) Fax: (+ 61) 3 83442384 E-mail : wwhwong@unimelb.edu.au [b] Dr. C.-Q. Ma, Prof.Dr. P. Bäuerle Institute for Organic Chemistry II and Advanced Materials University of Ulm Albert-Einstein-Allee 11 89081 Ulm (Germany) Fax: (+ 49) 731 50 22840 E-mail : changqi.ma@uni-ulm.de [c] Dr. W. Pisula, Dr. A. Mavrinskiy, Dr. X. Feng, Prof.Dr. K. Müllen Max Planck Institute for Polymer Research Ackermannweg 10 55128 Mainz (Germany) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201100211. Chem. Eur. J. 2011, 17, 5549 – 5560 # 2011 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim 5549 FULL PAPER