Small Molecule Organic Semiconductors on the Move: Promises for Future Solar Energy Technology

Abstract

This article is written from an organic chemist's point of view and provides an up-to-date review about organic solar cells based on small molecules or oligomers as absorbers and in detail deals with devices that incorporate planar-heterojunctions (PHJ) and bulk heterojunctions (BHJ) between a donor (p-type semiconductor) and an acceptor (n-type semiconductor) material. The article pays particular attention to the design and development of molecular materials and their performance in corresponding devices. In recent years, a substantial amount of both, academic and industrial research, has been directed towards organic solar cells, in an effort to develop new materials and to improve their tunability, processability, power conversion efficiency, and stability. On the eve of commercialization of organic solar cells, this review provides an overview over efficiencies attained with small molecules/oligomers in OSCs and reflects materials and device concepts developed over the last decade. Approaches to enhancing the efficiency of organic solar cells are analyzed.

Molecular-Scale Understanding of Cohesion and Fracture in P3HT:Fullerene Blends

“…Although there is increasing interest in the mechanical properties of BHJ active layers, [1][2][3][4][5][6][7][8][9] and such studies are common for traditional polymers, [10][11] the efforts in the OPV arena remain limited when compared to performance efficiency studies. [12][13][14][15][16] Along with the electronic processes involved in photocurrent generation, the active-layer mechanical properties inherently depend on the multiphase morphology of the BHJ thin films [17][18][19][20][21][22] and therefore are contingent on the thin-film processing protocols and the nature and strength of non-covalent, solid-state intermolecular interactions. However, a molecular-scale understanding of these properties, which is key to the design of more mechanically and electronically robust active layers, remains elusive.…”

The (Non-)Local Density of States of Electronic Excitations in Organic Semiconductors

“…Additionally, new design paradigms such as the donor-acceptor (DA) or acceptor-donor-acceptor (ADA) architecture for small molecules, oligomers and polymers aim for stronger optical absorption both in the visible and infrared region [30][31][32]. Long-wavelength absorbers furthermore assist efforts to integrate exciton fission as a single-photon multi-exciton generation process into OPV, with the perspective to go beyond the Shockley-Queisser limit for single-junction devices [33,34].…”

New generation solar cells: concepts, trends and perspectives

“…Research in the field was initiated in 2006, 45 and since then the synthesis of many classes of chromophores, such as oligothiophenes, triphenylamines, borondipyrromethene (BODIPY) diketopyrrolopyrroles, porphyrins, phthalocyanines and other p-conjugated molecules has been described. [46][47][48] As mentioned earlier, the most commonly used processing technique in smallmolecule OPVs is vacuum deposition, as a means to enhance charge transport capabilities and overcome insolubility phenomena. Solution processing (spin-coating, inkjet printing, dip-coating, spraying technique) has, however, also been employed, giving rise to a vast number of successful configurations.…”

“…6), but low efficiencies, attributed to the poor absorption characteristics of the material, were generally observed. 46,47a A number of other oligothiophene analogues and configurations have been prepared and tested, 48 with the best performance being reported recently by Bäuerle and co-workers with a novel Fig. 5 Structures of polymer PDTP-DFBT and ICBA fullerene, used together with P3HT (Fig.…”