All‐donor poly (arylene‐ethynylene) s containing anthracene and silole‐based units: Synthesis, electronic, and photovoltaic properties

The manuscript deals with the synthesis and properties of four new all-donor alternating poly(arylene-ethynylene)s DBSA, DBSTA, DTSA, and DTSTA. The polymers have been obtained by a Sonogashira cross-coupling of 9,10-diethynyl-anthracene with the dibromo-derivatives of 9,9-dioctyldibenzosilole (DBSA), 2,7-dithienyl-9,9-dioctyl-dibenzosilole (DBSTA), 4,4-dioctyl-dithienosilole (DTSA), or 2,6-dithienyl-9,9dioctyl-dithienosilole (DTSTA). The polymers exhibited absorption profiles and frontier orbital energies strongly dependent on their primary structure. Density functional theory calculations confirmed experimental observations and provided an insight into the electronic structure of the macromolecules. In particular, the effects exerted by the thiophene units in DBSTA and DTSTA on the optical properties of the corresponding INTRODUCTION The p-conjugated polymers have widely been employed as light-harvesting electron donor materials in bulk heterojunction (BHJ) solar cells, since they can be suitably designed to provide the necessary light harvesting as well as a favorable mixing with fullerene-based electron acceptors. 1 An ideal donor material for BHJ solar cells should possess the following requisites: (i) a broad absorption spectrum in the range of wavelengths where the solar photon flux is maximum (i.e., 500–800 nm); (ii) a thermodynamically feasible electron transfer to the acceptor materials (usually fullerene derivatives); (iii) an efficient hole transport; (iv) a relatively deep highest occupied molecular orbital (HOMO) energy. All these properties independently influence polymers could be rationalized with respect to DBSA and DTSA. Preliminary photovoltaic measurements have established that the performance of DTSA is among the highest reported for an all-donor polymer. Moreover, UV irradiation of DTSA films under air evidenced a remarkable photostability of this material, providing further evidence that ethynylenecontaining electron-rich systems are promising donors for organic solar cells applications.