Regulation of the Miscibility of the Active Layer by Random Terpolymer Acceptors to Realize High-Performance All-Polymer Solar Cells

Abstract

The main limitations on the power conversion efficiency (PCE) of all-polymer solar cells (all-PSCs) are the weak absorption coefficients of widely used naphthalene diimide (NDI)-based polymer acceptors and the difficulty of morphology control. Herein, a 3,3′-difluoro-2,2′-bithiophene (2FT) unit is introduced into the NDI-based polymer N2200 by random copolymerization, creating three terpolymer acceptors PNDI-2FT-0.1, PNDI-2FT-0.2, and PNDI-2FT-0.3. Incorporation of 2FT into the backbone is found to significantly improve the absorption coefficients of terpolymers. More importantly, it can be observed that random copolymerization of 2FT into the backbone not only can reduce the strong aggregation of the polymer but also can produce more flexible main chains to favor closer contact and better miscibility with the crystalline donor PBDB-T relative to the N2200 bipolymer. Under the optimal condition, a PBDB-T:PNDI-2FT-0.1-based device achieves a notable PCE of 9.46% with a short-circuit current (J SC) of 16.62 mA cm–2. Note that both the PCE and J SC are the outstanding values in NDI-based all-PSCs. Moreover, the optimized morphology of a bulk heterojunction induced by random terpolymers enables an active layer that has good thickness tolerance. These results demonstrate that the simultaneous regulation of light absorption and miscibility between a donor and an acceptor by random copolymerization is a promising strategy to realize high-performance all-PSCs.

Regioregularity-control of conjugated polymers: from synthesis and properties, to photovoltaic device applications

“…Thus, the light-absorption prole of random terpolymers with various chemical compositions can be tuned over a broad wavelength range. [119][120][121][122][123][124][125] Notably, the absorption coefficient of rre PDTSTTBDT is signicantly higher than that of rra polymer, indicating the highly efficient light harvesting capabilities. In addition to its optoelectrical properties, rre PDTSTTBDT exhibited higher order peaks in the GIXS pattern compared to that of the rra analog, suggesting that the molecular ordering of the D-A copolymers can be enhanced when the sequential RR is controlled.…”

Polymer Acceptors with Flexible Spacers Afford Efficient and Mechanically Robust All‐Polymer Solar Cells

“…Among these, ternary copolymerization provides effective means to modulate the solubility, optical property, energy level and aggregation behaviors of the P A s, and, thus, the blend morphology with the P D s. [ 27–32 ] For instance, Li et al developed random ternary PSMAs to improve the solubility, molecular crystallinity, and morphology of the blends. [ 33 ] Their all‐PSCs based on a P A containing 30% ester‐substituted thiophene as a third component exhibited better PCE and photostability as compared with those based on their parent P A .…”

Impact of Sequential Fluorination of Donor and/or Acceptor Polymers on the Efficiency and Morphology of All-Polymer Solar Cells

“…This is explained by the larger polarizability of small molecules than polymers, which links to the dispersion component, , whereas the polar component becomes predominant in the polymer:polymer blend. We have also calculated the Flory–Huggins interaction parameter (χ) according to the following equation reported in the previous literature with the SFE values of donor and acceptor components (γ donor and γ acceptor , respectively). − …”