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The high power-conversion efficiencies of hybrid perovskite solar cells encourage many researchers. However, their limited photostability represents a serious obstacle to the commercialization of this promising technology. Herein, we present an efficient method for improving the intrinsic photostability of a series of commonly used perovskite material formulations such as MAPbI3, FAPbI3, Cs0.12FA0.88PbI3, and Cs0.10MA0.15FA0.75PbI3 through modification with octenidine dihydroiodide (OctI2), which is a widely used antibacterial drug with two substituted pyridyl groups and two cationic centers in its molecular framework. The most impressive stabilizing effects were observed in the case of FAPbI3 and Cs0.12FA0.88PbI3 absorbers that were manifested in significant suppression or even blocking of the undesirable perovskite films' recrystallization and other decomposition pathways upon continuous 110 mW/cm2 light exposure. The achieved material photostability—within 9000 h for the Oct(FA)n−1PbnI3n+1 (n = 40–400) and 20,000 h for Oct(Cs0.12FA0.88)n−1PbnI3n+1 (where n = 40–400) formulations—matches the highest values ever reported for complex lead halides. It is important to note that the stabilizing effect is maintained when OctI2 is used only as a perovskite surface-modifying agent. Using a two-cation perovskite composition as an example, we showed that the performances of the solar cells based on the developed Oct(Cs0.12FA0.88)399Pb400I1201 absorber material are comparable to that of the reference devices based on the unmodified perovskite composition. These findings indicate a great potential of the proposed approach in the design of new highly photostable and efficient light absorbers. We believe that the results of this study will also help to establish important guidelines for the rational material design to improve the operational stability of perovskite solar cells. [ABSTRACT FROM AUTHOR]

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]

Two polymers with benzoxadiazole acceptor units were synthesized and investigated as electron donor materials in organic solar cells. Variation of the alkyl substituents was shown to significantly affect the optoelectronic properties of the polymers. In particular, the polymer HOMO energy level was lowered by 0.1 eV, while maintaining the same band gap, by replacement of the 2-ethylhexyl side-chains with the 2-hexyldecyl group. This modification also resulted in a higher open circuit voltage of the solar cells. [ABSTRACT FROM AUTHOR]

A series of ten conjugated polymers incorporating in their molecular frameworks extended DADAD building blocks with thiophene donor (D) and either benzotriazole, benzoxadiazole, benzothiadiazole, difluorobenzothiadiazole or quinoxaline acceptor (A) units were synthesized and characterized. The optoelectronic properties of new polymers were computed and experimentally investigated revealing a good relationship, which can guide further rational design of materials with tailored properties for organic photovoltaics using in-silico approaches. The performance of all polymers in organic bulk heterojunction solar cells was compared and some important empirical rules were formulated for reaching the best photovoltaic performance from (X-DADAD) n family of polymers. Image 1 • Conjugated polymers based on different acceptors have been synthesized. • Weak acceptor units result in wider band gaps and lower parameters of solar cells. • Good relationship between computed and experimental properties was revealed. [ABSTRACT FROM AUTHOR]

Two novel highly soluble bis(pyrrolidino)[60]fullerenes were synthesized and investigated as promising electron acceptor materials for organic solar cells. Reduced electron affinity of bis(pyrrolidino)[60]fullerenes as compared to the reference [60]PCBM enabled a spectacular increase in open-circuit voltage of organic bulk heterojunction solar cells by ~200 mV while using model P3HT and PCDTBT electron donor polymers. In addition to the improved optoelectronic properties, bis(pyrrolidino)[60]fullerenes were found to be resistant towards the photochemical cross-linking in contrast to conventional [60]PCBM and conjugated polymers. Most importantly, the designed fullerene derivatives efficiently suppressed photooxidation of conjugated polymers as revealed by ESR spectroscopy, which features a tremendous potential of applying these materials in the development of efficient and durable organic photovoltaics. ga1 • Two novel bis(pyrrolidino)[60]fullerenes are synthesized. • Bis(pyrrolidino)[60]fullerenes show better optoelectronic properties compared to PCBM. • Bis(pyrrolidino)[60]fullerenes are resistant towards the photochemical dimerization. • Bis(pyrrolidino)[60]fullerenes suppress photooxidation of conjugated polymers. [ABSTRACT FROM AUTHOR]

• Four novel methanofullerenes F1-F4 with decreased electron affinity are synthesized. • New adducts show better optoelectronic properties compared to [60]PCBM. • Solar cells with F1-F4 demonstrate increase in V OC by >100 mV and PCE. • F1-F4 have good compatibility with the amorphous conjugated polymer PCDTBT. Monocyclopropanated fullerene derivatives with decreased electron affinity as compared to standard [60]PCBM acceptor were synthesized, characterized, and investigated as promising electron acceptor materials for fullerene-based organic solar cells. This decrease in electron affinity was attributed to the presence of through-space electronic interactions between the lone electron pairs of oxygen atoms and electron-deficient π-system of the fullerene cage. Organic bulk heterojunction solar cells based on the designed materials blended with conjugated polymers P3HT and PCDTBT have demonstrated spectacular increase in open-circuit voltage by >100 mV and improved light power conversion efficiency as compared to the reference devices comprising [60]PCBM. The application of new fullerene-based acceptor materials in combination with the promising low band gap conjugated copolymer may deliver competitive device performances. [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]