Highly Efficient All‐Polymer Solar Cells Enabled by Random Ternary Copolymer Acceptors with High Tolerance on Molar Ratios

Abstract

Finding effective molecular design strategies and fine tuning the molar ratios of donor/acceptor (D/A) random copolymers to optimize the blend microstructure of the photoactive layer is one of the main long‐standing challenges in developing and fabricating highly efficient all‐polymer solar cells (all‐PSCs). Herein, a random ternary copolymerization strategy to develop four random copolymer acceptors PYEx (x = 10, 20, 30, 40) is used by polymerizing a fused‐ring A–D–A‐type acceptor unit modified from Y5 with a thiophene‐connecting unit and a controlled amount of an ester‐substituted thiophene (EST) unit. Compared with PYT (PYE0) of only Y5‐like units and thiophene units, the ternary copolymers PYEx show slightly down‐shifted lowest unoccupied molecular orbital (LUMO) energy levels, reduced absorption coefficients, and decreased electron mobilities. However, it is also demonstrated that this design approach rationally modifies the molecular aggregations of polymer acceptors, effectively fine tuning the blend morphology and physical mechanisms, and enhances the device performance of the PYEx‐based all‐PSCs. Among them, blends of PYE20 with donor polymer PBDB‐T combine 13.6% power conversion efficiency (PCE). Of particular note is that all of the PYEx‐based devices exhibit the best PCEs of over 13%, indicating the high tolerance on molar ratios.

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

“…The all‐PSC device based on the PBDB‐T:PYTS‐0.0 blend showed a PCE of 13.01% with an open‐circuit voltage ( V oc ) of 0.92 V and a J sc of 22.38 mA cm –2 , which is comparable to the reported values. [ 55 ] Notably, the all‐PSCs with PBDB‐T:PYTS‐0.3 blend showed a remarkably high PCE of 14.68% with a high J sc of 22.91 mA cm –2 , and FF of 0.70. However, the blends with high content of the FCBS units exhibited significantly low performances (with a PCE of 1.71% for the PBDB‐T:PYTS‐1.0‐based device).…”

Achieving over 17% efficiency of ternary all-polymer solar cells with two well-compatible polymer acceptors

“…To date, although enormous research efforts have been dedicated to developing near-infrared (NIR) P A s, 16,17,23 very few can afford impressive PCEs of over 14% in all-PSCs when blended with the P D PBDB-T derivatives (Table S1). 18,22,[24][25][26][27] Of note is that all these structures are based exclusively on one kind of electron-deficient unit (a Y5 derivative) (Figure S1). In addition, these P A s, formed by polymerization of a non-fullerene acceptor, generally retain the merits of SM-NFAs, such as strong absorbing properties and/or capabilities in the NIR region, tunable energy levels, and good charge transport properties.…”

High‐Performance All‐Polymer Solar Cells with a Pseudo‐Bilayer Configuration Enabled by a Stepwise Optimization Strategy

“…[ 25,26 ] Thus, reasonable use of different morphology control strategies, such as modification of molecular structures, [ 5,9,21,27 ] selection of solvent and additive, [ 6,20,28 ] thermal annealing, [ 6,22 ] and so on, to modify domain size and phase purity in all‐PSCs is critical. For instance, various random ternary copolymerization strategies were purposed to design P A derivatives, including naphthalene diimide (NDI)‐based N2200 derivatives (PNDI‐CBS 0.5 and BSS10), [ 21,29 ] and Y6‐like PSMAs (PTPBT‐ET 0.3 and PYE 0.2 ), [ 14,30 ] etc., for improving effectively phase‐separated BHJ morphologies. Nevertheless, the consumption and risk on trial and error experiments in terms of material design are huge.…”