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Abstract Five new donor-acceptor (X-DAD'AD) n type conjugated polymers have been synthesized using different X blocks based on carbazole, fluorene, silafluorene, benzodithiophene, and cyclopentadithiophene (CPDT). The strongly electron donating CPDT unit was used as a central D′ fragment to enhance intramolecular charge transfer interactions along the polymer backbone and reduce the bandgap of the resulting conjugated polymers. Apparently, the nature of the X block impacts the photophysical, morphological and optoelectronic properties of the designed polymers as well as their performance in bulk heterojunction solar cells. Fluorene-based copolymer P2 in combination with [70]PCBM delivered the best power conversion efficiency of 5.0% with a V OC of 0.78 V, a J SC of 11.1 mA/cm2 and a FF of 57%. Possibility for easy variation of the X and D′ blocks in the designed materials paves a way towards design of a variety of new materials for optoelectronic applications. Graphical abstract The proposed design strategy using a combination of two electron donor moieties (D and D′) with benzothiadiazole acceptor (A) units and different X blocks delivered a set of five new (X-DAD'AD) n conjugated polymers. The nature of the X block impacted the optoelectronic properties of the designed polymers as well as their performance in bulk heterojunction solar cells. fx1 Highlights • Novel (-X-DAD'AD) n type cyclopentadithiophene-based copolymers were synthesized. • Variation of X block strongly influences the optoelectronic properties of polymers. • Designed polymers delivered photovoltaic performances of 1.6–5.0% in solar cells. • The polymer structure strongly influences the V OC of the solar cells. [ABSTRACT FROM AUTHOR]

We report the synthesis and extensive investigation of a broad family of novel (X-DADAD) n conjugated polymers with different X building blocks. It was shown that variation of X block in polymer backbone represents an efficient approach for tuning the polymer optical properties, frontier energy levels, charge transport characteristics as well as thin-film morphology and photovoltaic characteristics. Decent power conversion efficiencies (5.1–5.7%) were achieved for solar cells based on the polymers comprised of dibenzosilole (P2) and carbazole (P3) units. Polymers P2 and P3 showed impressive indoor and outdoor stability in solar cells while clearly outperforming common benchmark materials. In the view of the obtained results, the designed (X-DADAD) n polymers can be considered as promising semiconductor materials for stable organic photovoltaics. Image 1 • Broad family of novel (X-DADAD) n conjugated polymers were designed and synthesized. • X block strongly influences optoelectronic and photovoltaic properties of polymers. • Dibenzosilole- and carbazole-based polymers deliver PCEs of ∼6%. • Two systems show impressive indoor and outdoor stability in solar cells. [ABSTRACT FROM AUTHOR]