to the advantages of non-flammability, reduced volatility, and improved environmental compatibility, [13][14][15] yielding a record PCE of over 7%. [16] In addition, integrated solar cell devices based on DSCs for ambient light harvesting and storage have sparked sharp increase of research attention due to the their mass production and commercial application for self-powering systems and portable electronics. [17][18][19][20] In recent years, DSCs with copper-complex-based redox mediator have achieved great progress, [21][22][23][24] especially the opencircuit voltage (V oc ) can reach now values over 1.0 V, comparable to that of the highperformance perovskite solar cells. [25][26][27][28] However, copper-electrolyte-based DSCs still suffer from relatively low short-circuit photocurrent (J sc ) issues, reducing their performance. The photosensitizer is the key component responsible for generation of the photocurrent, whose performance is determined by its visible light harvesting ability and charge generation efficiency. [10,[29][30][31] Therefore, developing tailored photosensitizers with superior photocurrent generation capability while maintaining high voltages becomes a key target to boost the DSC technology.Dithieno[3,2-b:2″,3″-d]pyrrole (DTP) has been reported as a potential conjugated linker for efficient DSCs with iodide/ triiodide or cobalt complexes as redox electrolytes. [32][33][34][35][36] It is worth noting that DTP is more easy and cheaper to synthesize than the conventional CDTP moiety providing over 90% yield in one step. [37,38] Compared to another commonly used linker, i.e., cyclopenta[1,2-b:5,4-b′]dithiophene (CPDT), that gives less than 30% yield over five steps, [39] it reflects the promise of DTP toward developing low-cost sensitizers for efficient DSCs. Importantly, DSCs employing the DTP-based dye LP225 show a comparable power conversion efficiency (PCE) to the CPDTbased dye Y123 with cobalt electrolyte, due to the increased V oc and improved charge-transfer kinetics of LP225 relative to Y123. In addition, another DTP-bridged dye G338 exhibits a better performance than the corresponding dye G337 with CPDT linker for cobalt-electrolyte-based DSCs. [33] These works reveal the potential of DTP as a key building block for efficient photosensitizers. However, the DTP-based sensitizers for copper-electrolyte-based DSCs have not been reported yet.Introducing additional electron-withdrawing groups into the dye structures, such as benzothiadiazole and quinoxaline Photosensitizers yielding superior photocurrents are crucial for copper-electrolyte-based highly efficient dye-sensitized solar cells (DSCs). Herein, two molecularly tailored organic sensitizers are presented, coded ZS4 and ZS5, through judiciously employing dithieno[3,2-b:2″,3″-d]pyrrole (DTP) as the π-linker and hexyloxy-substituted diphenylquinoxaline (HPQ) or naphthalenefused-quinoxaline (NFQ) as the auxiliary electron-accepting unit, respectively. Endowed with the HPQ acceptor, ZS4 shows more efficient electron injection and charge c...
Donor-acceptor (D-A) conjugated polymers are promising materials in optoelectronic applications, especially those forming ordered thin films. The processability of such conjugated macromolecules is typically enhanced by introducing bulky side chains, but it may affect their ordering and/or photophysical properties of the films. We show here the synthesis of surface-grafted D-A polymer brushes using alternating attachment of tailored monomers serving as electron donors (D) and acceptors (A) via coupling reactions. In such a stepwise procedure, alternating copolymer brushes consisting of thiophene and benzothiadiazole-based moieties with precisely tailored thickness and no bulky substituents were formed. The utilization of Sonogashira coupling was shown to produce densely packed molecular wires of tailored thickness, while Stille coupling and Huisgen cycloaddition were less efficient, likely because of the higher flexibility of D-A bridging groups. The D-A brushes exhibit reduced bandgaps, semiconducting properties and can form aggregates, which can be adjusted by changing the grafting density of the chains.
Alternating donor–acceptor conjugated polymers, widely investigated due to their applications in organic photovoltaics, are obtained mainly by cross-coupling reactions. Such a synthetic route exhibits limited efficiency and requires using, for example, toxic palladium catalysts. Furthermore, the coating process demands solubility of the macromolecules, provided by the introduction of alkyl side chains, which have an impact on the properties of the final material. Here, we present the synthetic route to ladder-like donor–acceptor polymer brushes using alternating copolymerization of modified styrene and maleic anhydride monomers, ensuring proper arrangement of the pendant donor and acceptor groups along the polymer chains grafted from a surface. As a proof of concept, macromolecules with pendant thiophene and benzothiadiazole groups were grafted by means of RAFT and metal-free ATRP polymerizations. Densely packed brushes with a thickness up to 200 nm were obtained in a single polymerization process, without the necessity of using metal-based catalysts or bulky substituents of the monomers. Oxidative polymerization using FeCl3 was then applied to form the conjugated chains in a double-stranded (ladder-like) architecture.
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