We design and synthesize a series of high-mobility n-type polyelectrolytes with different anions via quaternisation polymerisation, which can be utilized as thickness-insensitive electron-transporting materials for polymer solar cells.

An easy and efficient approach to achieve a large-area cathode interlayer with controlled film composition, uniformity, and thickness under a nanometer scale is reported by using an electrostatic layer-by-layer (eLbL) self-assembly process. The eLbL films provide a new means for preparing efficient interlayers for polymer solar cells (PSCs) and also represent a potential candidate for use in high-performance large-area PSC modules in the future.

Materials by design are expected to deliver optimized performance for well-defined applications. [1,2] In most cases, the performance of a material depends on the chemical structure and kinetic processes that control the morphology formed, making material design a challenge to directly relate chemical structure to performance. Examples are seen in semiconducting polymers. While the conjugated backbone provides optoelectronic function, side chains, substitution groups, and molecular geometry are factors that dictate how the material will assemble. [3][4][5][6][7][8] When making multicomponents blends, as in the active layer of bulk heterojunction organic photovoltaics (OPV), elucidation of the structure of conjugated polymers and their interactions with fullerenes or other type of acceptors is essential. [9][10][11][12][13] Optimization of a material is, more often than not, a search in a multidimensional space. As seen with the PTBx series of electron donors, the quinoid resonance backbone improved solar light harvesting. [14] Side chain optimization and fluorine atom regioregularity tuning further improved the performance of the materials. [15,16] Donor-acceptor (D-A) conjugated polymers have had tremendous success in generating high power conversion efficiencies in organic solar cells, but required a fine tailoring of the chemical structure to ensure suitable energy levels and to enable intramolecular charge transfer (ICT). [17,18] The D-A conjugated polymers are commonly prepared in a one-pot synthesis through a condensation of A2+B2 intermediates, which inevitably leads to geometric defects if asymmetric monomers are used. Monofluorinated monomers, such as thieno[3,4-b] thiophene (FTT), benzothiadiazole (FBT), and pyridalthiadiazole are well-known high performance units. [16,[19][20][21] However it is essential to be able to minimize or eliminate batch-to-batch variations in the geometry and conformation of the backbone to reliably establish a structure-property relationship, so as to enable the generation of materials by design.Here we present the synthesis of unidirectional, high regioregular conjugated polymers using 5-fluoro-2,1,3-benzothiadiazole (FBT) asymmetric unit. By unidirectional we mean that positioning of the fluorine atom is always at the same position relative to the direction of the chain, which, as will be discussed, orients the dipole in each unit in the same direction. Consequently, the dipole moment would accumulate along the The chemical structure of conjugated polymers plays an important role in determining their physical properties that, in turn, dictates their performance in photovoltaic devices. 5-Fluoro-2,1,3-benzothiadiazole, an asymmetric unit, is incorporated into a thiophene-based polymer backbone to generate a hole conducting polymers with controlled regioregularity. A high dipole moment is seen in regioregular polymers, which have a tighter interchain stacking that promotes the formation of a morphology in bulk heterojunction blends with improved power conversion efficiencie...

No abstract

A series of naphthalene diimide (NDI) based n-type conjugated polymers with amino-functionalized side groups and backbones were synthesized and used as cathode interlayers (CILs) in polymer and perovskite solar cells. Because of controllable amine side groups, all the resulting polymers exhibited distinct electronic properties such as oxidation potential of side chains, charge carrier mobilities, self-doping behaviors, and interfacial dipoles. The influences of the chemical variation of amine groups on the cathode interfacial effects were further investigated in both polymer and perovskite solar cells. We found that the decreased electron-donating property and enhanced steric hindrance of amine side groups substantially weaken the capacities of altering the work function of the cathode and trap passivation of the perovskite film, which induced ineffective interfacial modifications and declining device performance. Moreover, with further improvement of the backbone design through the incorporation of a rigid acetylene spacer, the resulting polymers substantially exhibited an enhanced electron-transporting property. Upon use as CILs, high power conversion efficiencies (PCEs) of 10.1% and 15.2% were, respectively, achieved in polymer and perovskite solar cells. Importantly, these newly developed n-type polymers were allowed to be processed over a broad thickness range of CILs in photovoltaic devices, and a prominent PCE of over 8% for polymer solar cells and 13.5% for perovskite solar cells can be achieved with the thick interlayers over 100 nm, which is beneficial for roll-to-roll coating processes. Our findings contribute toward a better understanding of the structure-performance relationship between CIL material design and solar cell performance, and provide important insights and guidelines for the design of high-performance n-type CIL materials for organic and perovskite optoelectronic devices.