On the Importance of Morphology Control in Polymer Solar Cells

Abstract

Nanostructured polymer-based solar cells (PSCs) have emerged as a promising low-cost alternative to conventional inorganic photovoltaic devices and are now a subject of intensive research both in academia and industry. For PSCs to become practical efficient devices, several issues should still be addressed, including further understanding of their operation and stability, which in turn are largely determined by the morphological organisation in the photoactive layer. The latter is typically a few hundred nanometres thick film and is a blend composed of two materials: the bulk heterojunction consisting of the electron donor and the electron acceptor. The main requirements for the morphology of efficient photoactive layers are nanoscale phase segregation for a high donor/acceptor interface area and hence efficient exciton dissociation, short and continuous percolation pathways of both components leading through the layer thickness to the corresponding electrodes for efficient charge transport and collection, and high crystallinity of both donor and acceptor materials for high charge mobility. In this paper, we review recent progress of our understanding on how the efficiency of a bulk heterojunction PSC largely depends on the local nanoscale volume organisation of the photoactive layer.

Morphological Characterization of a Low‐Bandgap Crystalline Polymer:PCBM Bulk Heterojunction Solar Cells

“…While there have been advances in the synthesis of novel low bandgap polymers and block copolymers with tailored morphologies, translating these advances to large scale production mandates understanding the morphology of the active layer developed during processing, the relationship of the morphology to device performance, and routes to tailor the morphology to optimize effi ciency. [1][2][3][4] Controlling the morphology is made even more challenging, since the morphology of the active layer is far-removed from equilibrium, resulting from a competition between the ordering of the photoactive polymer, the phase separation of the components, the rate of solvent evaporation, and the mobility and inter facial segregation of the components. [ 5 , 6 ] The most-studied donor-acceptor combination for polymer solar cells is a blend of poly(3-hexylthiophene) (P3HT) and [6,6]phenyl-C 61 -butyric acid methyl ester (PCBM), solution cast from 1,2-dichlorobenzene ( o -DCB), where subsequent thermal annealing at temperatures well below the melting point of P3HT significantly improves device performance.…”

Structure‐Property Optimizations in Donor Polymers via Electronics, Substituents, and Side Chains Toward High Efficiency Solar Cells

“…These reviews have covered various aspects of this interdisciplinary research fi eld, such as design of polymers, [26][27][28] device physics, [ 29,30 ] physical chemistry, [ 31,32 ] morphology control, [33][34][35][36][37][38][39] and stability/economics. [ 40,41 ] Rather than contributing another comprehensive review, we attempt to direct the readers' attention to the latest advances in the design of new polymeric materials for BHJ solar cells.…”

Charge transport and recombination in PDPP5T:[70]PCBM organic solar cells: The influence of morphology

“…As a result of this self-assembly, charge-sepa-88 rating heterojunctions are formed throughout the bulk of 89 the material [15]. 90 The morphology of the active layer plays a fundamental 91 role in determining the efficiency of BHJs [17][18][19]. Genera-92 tion and transport of free charge carriers depends on size 93 [20][21][22], composition [22][23][24] and crystallinity [25,26] [30][31][32], co-solvent [29,34] and addi-103 tives [33], as well as the effect of post-fabrication treat-104 ments, e.g.…”