The emergent perovskite photovoltaics technology faces challenges like the long-term durability combining moisture, thermal, and photo stresses that prevents them from competing with established technologies. Here, we introduce a series of new fluorinated fullerenes as an electron-transporting layer (ETL) for robust perovskite photovoltaics that deliver a high power conversion efficiency of 21.27% with substantially improved durability against environmental stressing. The hydrophobic nature of the new fullerene protects the unencapsulated perovskite cell with stability over 1400 h in 85% relative humidity. Notably, the unencapsulated device maintained 80% of their original performance (T80) after being immersed in water for over 10 min. Detailed characterizations suggest that the fluorinated fullerene can immobilize the cations in perovskites and passivate the surface traps. Therefore, the T80 lifetime of the devices under constant illumination reached 1920 h. On the basis of the accelerated test, we estimate a lifetime approaching 10 years with encapsulation. The successful demonstration of the new ETL can stimulate further research and momentum for future photovoltaic technology development.

Fluorinated PC61BM can be used to fabricate BHJ perovskite films in one step using one solvent in a BHJ precursor solution system.

The effects of the spatial arrangement of the conjugated side chains of two-dimensional polymers on their optical, electrochemical, molecular-packing, and photovoltaic characteristics were investigated. Accordingly, novel polythiophenes with horizontally (PBTTTV-h) and vertically (PBTTTV-v) grafted terthiophene–vinylene (TTV) conjugated side chains were synthesized that display two and one UV-vis peaks, respectively; the difference is due to the different constitutions of the conjugated side-chains. Because the spatial arrangement affects the molecular self-assembly, PBTTTV-h shows stronger crystallinity than PBTTTV-v, which enhances the charge mobility in devices. Moreover, PBTTTV-h has a lower HOMO energy level (−5.49 eV) than PBTTTV-v (−5.40 eV). Bulk heterojunction solar cells fabricated from PBTTTV-h/PC71BM and PBTTTV-v/PC71BM exhibit power conversion efficiencies of 4.75% and 4.00%, respectively, and Voc values of 800 and 730 mV, respectively, under AM1.5G illumination (100 mW cm(−2)). Thus, the architecture of the TTV conjugated side chains affects the optical, electrochemical, and photovoltaic properties; this study provides more ideas for improving 2-D conjugated polymers for semiconductor devices.

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Forming nano-scale interpenetrating networks in electron donor/acceptor blends via phaseseparation tuning and maintaining their optimal morphology are of paramount importance for the favorable performance and operational lifetime of bulk heterojunction (BHJ) polymer solar cells. In this work, two fulleropyrrolidine derivatives that bear π-conjugated terthiophene (3T) and two hexyl (H) or ethylhexyl (EH) chains, abbreviated as 3T-H-C 60 and 3T-EH-C 60 , are separately used as a compatibilizer of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM). The effect of the loading of such an agent on the photovoltaic properties of solar devices and the morphological stability of the P3HT/PCBM blend was examined. The substitution of PCBM with a tiny amount of 3T-H-C 60 or 3T-EH-C 60 apparently enhances the short-circuit current density, reflecting the formation of small PCBM clusters within the P3HT matrix. More importantly, optical microscopy, transmission electron microscopy and photoluminence measurements verify that the presence of 1 wt% 3T-H-C 60 or 3 wt% 3T-EH-C 60 effectively hinders the thermal motion of PCBM molecules to form micro-scale clusters, leading to an extremely stable morphology even under long-term exposure to elevated temperatures. Accordingly, the power conversion efficiencies of P3HT/PCBM:3T-H-C 60 and P3HT/PCBM:3T-EH-C 60 devices remain very steady during prolonged aging at 130 °C. This work provides valuable guidelines for the design of an effective compatibilizer for thermally stable polymer/fullerene BHJ solar cells.Recently, several efforts have been made to establish a rational strategy for improving the environmental stability of solar devices by stabilizing the bulk-heterojunction (BHJ) film morphology.Sivula et al. applied a small amount of dihexyl-functionalized thiophene as a co-monomer to reduce the regioregularity of P3HT from >96% to 91%, to suppress the crystallization-induced phase separation and enhance the thermal stability of BHJ devices 15 . Kim et al. copolymerized 2-bromo-3-(6bromohexyl)thiophene and 2-bromo-3-hexylthiophene to prepare bromine-functionalized P3HT, which can be cross-linked upon irradiation under UV light, restricting the thermal motion of fullerene acceptors and the consequent formation of large clusters, preserving long-term performance 16 . Bertho et Terthiophene-C 60 dyad can be used as promising compatibilizer to suppress the thermal motion of PCBM inside the P3HT matrix, leading to an extremely robust morphology.

Molecular engineering on the conjugated side chains of two-dimensional (2D) conjugated polymers was conducted and its effect on the optical, electronic, self-assembly and photovoltaic properties was investigated. A new monomer, M2, was prepared by capping (E)-3 0 -(2-(2,5-dibromothiophen-3-yl)vinyl)-4,4 00 -bis(2-ethylhexyl)-2,2 0 :5 0 ,2 00 -terthiophene, M1, with two heptanoyl groups, and then coupled with 5,5 0 -bis(trimethylstannyl)-2,2 0 -bithiophene via microwave-assisted Stille polymerization to produce a series of polythiophene derivatives with terthiophene-vinylene conjugated side chains, TTV-PTs.Copolymer P2 shows a down-shifted HOMO energy level, enhanced solubility, and red-shifted absorption, as compared with P1; however, the bulky side chains significantly disrupt the coplanarity of thiophene rings in the polymer backbone and the ability to self-assemble into an ordered structure. The GIXRD measurements reveal that the original crystallinity of P1 can be recovered by simply inserting a few 2,1,3-benzothiadiazole units into the polythiophene main chain in P2 through a random copolymerization route to yield a terpolymer, P3, which possesses excellent crystallinity, thereby causing a three-fold increment in hole mobility. Furthermore, the P1/PC 61 BM, P2/PC 61 BM, and P3/PC 61 BM solar devices exhibit power conversion efficiencies of 3.89%, 1.52%, and 4.17%, respectively, under AM1.5G illumination with an intensity of 100 mW cm À2 .

Conversion of CO2 into carbonaceous fuels with the aid of solar energy has been an important research subject for decades. Owing to their excellent electron‐accepting capacities, fullerene derivatives have been extensively used as n‐type semiconductors. This work reports that the fulleropyrrolidine functionalized with 4,7‐di(thiophen‐2‐yl)benzo[c][1,2,5]thiadiazole, abbreviated as DTBT‐C60, could efficiently catalyze the photoreduction of CO2 to CO. The novel C60‐chromophore dyad structure facilitated better usage of solar light and effective dissociation of excitons. Consequently, the DTBT‐C60 exhibited a promising CO yield of 144 μmol gcat−1 under AM1.5G solar illumination for 24 h. Moreover, the isotope experiments demonstrated that water molecules could function as an electron source to reactivate DTBT‐C60. Impressively, DTBT‐C60 exhibited an extremely durable catalytic activity for more than one week, facilitating the practical application of photochemical CO2 reaction.

A series of novel p-type conjugated copolymers, PTTVBDT, PTTVBDT-TPD, and PTTVBDT-DPP, cooperating benzo[1,2-b:4,5-b ]dithiophene (BDT) and terthiophene-vinylene (TTV) units with/without thieno [3,4-c]pyrrole-4,6-dione (TPD) or pyrrolo [3,4-c]pyrrole-1,4-dione (DPP) via Stille polymerization were synthesized and characterized. Copolymer PTTVBDT shows a low-lying HOMO energy level and ordered molecular-packing behavior. Furthermore, two terpolymers, PTTVBDT-TPD and PTTVBDT-DPP, display stronger absorption ability, alower-lying HOMO energy level, and preferred molecular orientation, due to the replacement TTV-monomer units with electron-deficient groups. Furthermore, bulk-heterojunction organic solar cells were fabricated using blends of the PTTVBDT-TPD, and PC 61 BM gave the best power conversion efficiency of 5.01% under the illumination of AM 1.5G, 100 mW·cm −2 ; the short circuit current (J sc ) was 11.65 mA·cm −2 which displayed a 43.8% improvement in comparison with the PTTVBDT/PC 61 BM device. These results demonstrate a valid strategy combining the two-dimensional molecular structure with random copolymerization strikes promising conjugated polymers to achieve highly efficient organic photovoltaics.