Using Pentaarylfullerenes to Understand Network Formation in Conjugated Polymer-Based Bulk-Heterojunction Solar Cells

Abstract

We have synthesized a series of pentaarylfullerene derivatives and incorporated them into bulk-heterojunction (BHJ) solar cells using poly(3-hexylthiophene) as the electron donating material. Through a combination of grazing incidence X-ray diffraction and atomic force microscopy we see two distinct nanoscale morphologies emerge across the series. Investigating the device physics using J–V characterization, light intensity dependence, and fluorescence quenching studies, we are able to correlate the morphology to the device physics. This has afforded the opportunity to clearly see how altering the nanoscale phase segregation can change the distinct physical processes occurring within a BHJ solar cell. We observe an order of magnitude increase in the efficiency of devices that utilize self-assembling fullerene derivatives over their nonassembled counterparts. More importantly, however, these results allow us to shed light on the mechanism behind this differential phase segregation using a fullerene self-assembly model. On the basis of the data, we propose new design rules for the structure of future generations of fullerene electron accepting materials for use in BHJ solar cells.

Crystal‐Packing Trends for a Series of 6,9,12,15,18‐Pentaaryl‐1‐hydro[60]fullerenes

“…However, for further advancement in this area, innovative approaches to developing novel fullerene acceptors are necessary and are starting to emerge 2d,g,j–m. 3, 8, 9…”

“…The parameters affecting molecular interactions between pentaarylfullerenes in the solid state needed to be investigated in more depth 8. 9 The present study scrutinizes the crystal‐packing trends for a series of chemically and structurally related pentaarylfullerenes ( 1 a – o ), focusing on the robustness of stacking motifs, that is, the propensity of each pentaarylfullerene derivative to form a solvent‐independent stacking motif (universal stacker). In addition, factors such as the density of short C⋅⋅⋅C contacts (below the sum of the van der Waals radii) between the π systems of two fullerene moieties and the dimensionality of the close‐contact networks they constitute have been analyzed.…”

Fullerenes and carbon nanotubes as acceptor materials in organic photovoltaics

“…Recent work on pentaarylfullerenes (PAFs) demonstrates that changing the substituent can result in fullerenes that form columnar stacks [58,59]. Blends of P3HT with these stacking fullerenes exhibit significantly enhanced short-circuit current densities compared to PAFs with substituents that prevent stacking.…”

“…Blends of P3HT with these stacking fullerenes exhibit significantly enhanced short-circuit current densities compared to PAFs with substituents that prevent stacking. It was proposed that a competition between the propensity of the PAF to form columnar stacks, and the semicrystalline P3HT to form crystallites, creates a favorable interpenetrating network of polymer and fullerene phases in the blend film [59]. By contrast, the morphology in blends with non-stacking PAFs seems to be dominated by crystallization of the polymer, resulting in coarsely phase-separated domains and accordingly poor OPV device performance [59].…”

Pentaarylazafullerene und ihre Triaryldihydro‐ und Tetraarylmonohydro‐Zwischenstufen

“…[2] Im Gegensatz zu der reichhaltigen Vielfalt von hçheren C 60 -Addukten und deren zugehçrigen Additionsmustern sind hçhere Azafullerenaddukte kaum beschrieben. [7] Hçhere Azafullerenaddukte mit einem zu den C 60 -Derivaten vergleichbaren Pentaadditionsmuster wurden erstmals in der Arbeitsgruppe Hirsch entdeckt, indem C 59 NAr-Addukte 3 mit einem Überschuss an ICl umsetzt wurden, was zu tetrachlorierten Aryladdukten C 59 NArCl 4 mit einer isolierten Pyrrolunterstruktur führt. Neben der Vielzahl an Fullerenderivaten ist dieses Additionsmuster einzigartig: Einer der Fünfringe des Fullerengerüsts wird vom restlichen p-System isoliert, und es entsteht somit eine im Fullerengerüst eingebettete Cyclopentadien-Struktureinheit, die wiederum nach Deprotonierung mit einer Vielfalt an Übergangsmetallen komplexiert werden kann.…”