Branched Electron-Donor Core Effect in D-π-A Star-Shaped Small Molecules on Their Properties and Performance in Single-Component and Bulk-Heterojunction Organic Solar Cells †

Abstract

Star-shaped donor-acceptor molecules are full of promise for organic photovoltaics and electronics. However, the effect of the branching core on physicochemical properties, charge transport and photovoltaic performance of such donor-acceptor materials in single-component (SC) and bulk heterojunction (BHJ) organic solar cells has not been thoroughly addressed. This work shows the comprehensive investigation of six star-shaped donor-acceptor molecules with terminal hexyldicyanovinyl blocks linked through 2,2′-bithiophene π-conjugated bridge to different electron-donating cores such as the pristine and fused triphenylamine, tris(2-methoxyphenyl)amine, carbazole- and benzotriindole-based units. Variation of the branching core strongly impacts on such important properties as the solubility, highest occupied molecular orbital energy, optical absorption, phase behavior, molecular packing and also on the charge-carrier mobility. The performance of SC or BHJ organic solar cells are comprehensively studied and compared. The results obtained provide insight on how to predict and fine-tune photovoltaic performance as well as properties of donor-acceptor star-shaped molecules for organic solar cells.

Effect of oligothiophene π-bridge length in D-π-A star-shaped small molecules on properties and photovoltaic performance in single-component and bulk heterojunction organic solar cells and photodetectors

“…The LUMO energies were found to be significantly lowered from À3.25 to À3.40 eV with inclusion of the first thiophene unit, whereas no significant impact of further pbridge elongation was observed. The latter can be explained by the fact that the electrochemical reduction proceeds mainly on the terminal alkyl-dicyanovinyl fragment [39,44], the local environment of which does not change significantly with the oligothiophene p-bridge elongation. Thus, the electrochemical bandgap within 0Te4T series of molecules decreases from 2.38 eV to 1.85 eV, which is in a good agreement with the optical absorption data (Table S4.1).…”

“…The star-shaped architecture in design of D-A small molecules brings a number of advantages over the linear architecture [18,36e38]. Star-shaped D-A organic molecules based on the triphenylamine (TPA) core possess promising properties such as high stability and hole mobility, good solubility in organic solvents [13,19,39,40]. Roncali et al [41,42] published pioneering works on synthesis and OSC application of star-shaped D-A small molecules based on the TPA donor core linked through monothiophene and bithiophene bridges to terminal dicyanovinyl electronwithdrawing groups.…”

Structure–properties of small donor–acceptor molecules for homojunction single-material organic solar cells

“…27 Although the low efficiency of primitive HOSCs 4 has severely hampered research in this direction, some recent reports suggest of renewal of interest in this of topic. [28][29][30][31][32][33][34][35][36][37] Research on HOSCs is a high-risk challenge but the knowledge accumulated during a half-century of OSC research represents a valuable intellectual capital which makes it possible to consider the problem on new bases. Charge-generation is the key problem posed by HOSCs.…”

“…29 D-A intramolecular interactions can also contribute to charge separation. 28,[30][31][32][33][34][35][36][37][38][39][40] In this case, the possible exciton dissociation on the molecular site of photon absorption could pave the way towards non ) excitonic * OSCs, 41 and thus erase some of the major problems posed by multi-component cells. HOSCs based on subphthalocyanines, 28 A-D-A 30,31 or star-shaped D-A systems [32][33][34][35][36] have been reported, however, simple small D-A molecules already investigated in multicomponent OSCs, 10,13 have been investigated only in one publication.…”

“…28,[30][31][32][33][34][35][36][37][38][39][40] In this case, the possible exciton dissociation on the molecular site of photon absorption could pave the way towards non ) excitonic * OSCs, 41 and thus erase some of the major problems posed by multi-component cells. HOSCs based on subphthalocyanines, 28 A-D-A 30,31 or star-shaped D-A systems [32][33][34][35][36] have been reported, however, simple small D-A molecules already investigated in multicomponent OSCs, 10,13 have been investigated only in one publication. 37 In this context, we report herein a first systematic analysis of structure-properties relationships on a homogeneous series of small D-A molecules consisting of a triarylamine donor block connected to dicyanovinyl (DCV) and indanedione-based acceptors by thienyl and phenyl conjugating bridges (Scheme 1).…”