Conjugation-break spacers (CBS) have been shown to enhance the mechanical properties of conjugated polymers. In particular, incorporation of CBS units into semi-random polymers has revealed high ductility and low elastic moduli, attributed to the combined influence of the CBS units and the semi-random architecture. To further elucidate the structure–property relationships in these polymers, two new families of semi-random polymers are reported here. In the first, poly­(3-hexylthiophene)-based semi-random polymers incorporating diketo­pyrrolopyrrole (DPP) units were synthesized in which CBS units with 4–10 carbons were incorporated from 10 to 40% with an equivalent content of 2-decyltetradecyl-DPP (dtdDPP) to overcome solubility limitations previously observed with 2-ethylhexyl-DPP (ehDPP). These polymers had much higher solubility and could attain higher molecular weights, formed films with high integrity, and displayed extraordinary mechanical properties, with elastic moduli as low as 5.45 MPa and fracture strains as high as 398%. In the second family, the content of ehDPP was held constant at 10%, while the CBS content was varied from 10 to 50% (with an eight-carbon spacer) to deconvolute the influence of CBS and DPP content on mechanical properties. Polymer solubility, molecular weight, and processability were not shown to improve dramatically relative to the previous generation of ehDPP polymers with matched DPP and CBS content, but the mechanical properties of this series were quite notable, with elastic moduli as low as 4.08 MPa, an increase in toughness, and fracture strains as high as 432%. The extraordinary mechanical properties exhibited by these polymers can serve as a guide in the judicious selection of monomers and backbone architectures in the future synthesis of semiconducting polymers for flexible electronic applications.

Organic solar cells based on multinary components are promising to further boost the device performance. The complex interplay of the morphology and functionality needs further investigations. Here, we report on a systematic study on the morphology evolution of prototype ternary systems upon adding sensitizers featuring similar chemical structures but dramatically different crystallinity, namely poly­(3-hexyl­thiophene) (P3HT) and indene-C60-bis-adduct (ICBA) blends with poly­[(4,4′-bis­(2-ethylhexyl)­dithieno­[3,2-b:2′,3′-d]­silole)-2,6-diyl-alt-(4,7-bis­(2-thienyl)-2,1,3-benzo­thiadi-azole)-5,5′-diyl] (Si-PCPDTBT) and poly­[2,6-(4,4-bis­(2-ethyl­hexyl)-4H-cyclopenta­[2,1-b;3,4-b′]-dithiophene)-alt-4,7-(2,1,3-benzo­thiadiazole)] (C-PCPDTBT), employing energy-filtered transmission electron microscopy (EFTEM) and resonant soft X-ray scattering (RSoXS). In addition, a combined density functional theory (DFT) and artificial neuronal network (ANN) computational approach has been utilized to calculate the solubility parameters and Flory–Huggins intermolecular parameters to evaluate the influence of miscibility on the final morphology. Our experiments reveal that the domain spacing and purity of ICBA-rich domains are retained in Si-PCPDTBT-based systems but are strongly reduced in C-PCPDTBT-based ternary systems. The P3HT fiber structure are retained at low sensitizer content but dramatically reduced at high sensitizer content. The theoretical calculations reveal very similar miscibility/compatibility between the two sensitizers and ICBA as well as P3HT. Thus, we conclude that mainly the crystallization of Si-PCPDTBT drives the nanostructure evolution in the ternary systems, while this driving force is absent in C-PCPDTBT-based ternary blends.

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Here, brand new ternary hybrid solar cells comprising perovskite nanocrystals (NCs) with a complementary absorption profile of the organic host matrix are reported. In particular, NH2CH[double bond, length as m-dash]NH2PbI3 (FAPbI3) perovskite NCs are implemented in bulk heterojunction organic solar cells based on the pDPP5T-2 electron donating polymer and a [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) acceptor at various loading amounts and the fabricated hybrid photovoltaics are thoroughly studied by employing different optoelectrical characterization methods. Current-voltage measurements and photoinduced charge carrier extraction by linear increasing voltage (photo-CELIV) reveal improved charge generation and charge transport properties upon incorporation of perovskite NCs into the photo-active layer of the hybrid solar cell. The power conversion efficiency (PCE) of the hybrid solar cell comprising 5% perovskite NCs is 10% enhanced compared to the organic reference, mainly due to the enlarged light harvesting and increased short circuit current density (Jsc). However, results suggest that introducing a higher amount of perovskite content induces bimolecular and trap-assisted recombination in the ternary devices. We perform a comprehensive transient absorption study of the charge transfer/transport mechanisms by employing femto-second pump-probe transient absorption spectroscopy (fs-TAS). fs-TAS measurements demonstrate a slower charge carrier recombination rate due to the introduction of perovskite NCs into the photoactive layer. Results reveal that DPP injects electrons from the singlet excited state into the perovskite NCs, which causes the desired cascading charge carrier transfer. In ternary blends, a small amount of FAPbI3 NCs provides an additional pathway in favor of the charge-separated state via the NCs, which, despite accelerating the depopulation of DPP's singlet excited state slightly slows down the charge-separation process between DPP and PC61BM. Interestingly, the loss processes are slowed down; an effect that is more important and, hence, explains the improved solar cell efficiency.