Achieving High-Efficiency Organic Photovoltaics from a New Completely Amorphous Donor Polymer

Abstract

The development of non-fullerene acceptors (NFAs) such as ITIC and Y6 has greatly improved the efficiency of polymer solar cells. Therefore, focus should now shift towards the design of donor polymers with better compatibility with these NFAs to attempt to push efficiencies to higher levels. The indacenodithienothiophene (IDT) unit has up till now been typically incorporated into donor polymers for fullerene-based solar cells; however, the application of IDT-based polymers in NFA solar cells is rare. In order to increase the number of donor polymer candidates, we have synthesized two new polymers PIDT-T8BT and PIDT-T12BT conjugating IDT and perfluorinated benzothiadiazole moieties through octyl and dodecyl thiophene bridging units, respectively. These polymers were studied and revealed to be completely amorphous without aggregates, and their glass transition temperatures were distinct owing to the different lengths of the alkyl groups attached to the thiophene units. In addition, the length of the side groups greatly affects the solar cell performance. The longer dodecyl side groups in the polymer PIDT-T12BT resulted in a lower glass transition temperature and favorable thermal annealing conditions of the active layer blend with Y6. A promising power conversion efficiency of over 12% was achieved for PIDT-T12BT when paired with the Y6 acceptor and thermally annealed at 170 °C, which is the highest reported value so far for IDT-based donor polymers.

Mechanically Adaptive Mixed Ionic-Electronic Conductors Based on a Polar Polythiophene Reinforced with Cellulose Nanofibrils

“…Tensile elastic modulus at room temperature vs the T g of p­(g 4 2T-T) from ref (blue open circle), of conjugated polymers with alkyl side chains from refs − (blue filled symbols) and refs , [blue half-filled symbols; tensile elastic modulus estimated using E = 2 G (1 + υ ), where G is the shear elastic modulus and assuming a Poisson ratio of υ = 0.5] as well as the value measured in this study for p­(g42T-T) (pink open diamond), which increases by at least two orders of magnitude (red arrow) upon the addition of 11 or 20 vol % CNF (pink filled diamonds).…”

Enhanced Photocatalytic and Photovoltaic Performance Arising from Unconventionally Low Donor–Y6 Ratios

“…Previous studies of the Y6 system have shown it is ambipolar, with the mobility of electrons reported to be a factor of 2-3 times greater than that of holes in intrinsic Y6-only devices. [22,56] Both the Y6 hole mobility reported in these studies and the PIDT-T8BT hole mobility reported in our previous work are lower than the maximum carrier mobility determined in this work, [24] leading us to assign the mobility measured by photoCE-LIV to electron transport in Y6. To rationalize why this mobility increased by more than an order of magnitude as the D:A ratio was increased from the 1:50 to the 1:1, we consider both the complex nature of charge generation and recombination revealed by the TA measurements in this work and the data and interpretations reported in previous studies of low donor-content devices with Y6 as an electron acceptor.…”

“…However, the PIDT-T8BT:Y6 solar cells using the conventional donor:acceptor (D:A) ratio of 1:1.2 only offered modest photovoltaic performance, which discouraged the continued study of this polymer. [24] Inspired by the studies on low donor blends paired with Y6, [22][23] a series of OPVs containing PIDT-T8BT:Y6 over a broad range of D:A ratios were fabricated and investigated for this study. In this work, PIDT-T8BT:Y6 OPVs with a D:A ratio of 1:10 achieved over 10% PCE.…”

Real-time correlation of crystallization and segmental order in conjugated polymers

“…9,10 In the past decade, with the advent of more complex monomer structures, researchers found that, instead of long-range ordering (i.e., crystalline packing), the local segmental order (e.g., co-facially stacked planar backbone segments with tie polymer chains) can enable efficient long-range charge transport in a near amorphous state. [11][12][13] This unique charge transport mechanism might result from the high coplanarity of rigid backbone with long conjugation length, which in turn allows CPs to have more design space for coupling new functions, such as mechanical softness and stretchability, while maintaining electronic performance. 14 It is immediately evident that the segmental order strongly depends on the chain rearrangement, especially the crystallization process, during deposition and post-thermal treatment.…”