New medium bandgap donor D-A1 -D-A2 type Copolymers Based on Anthra[1,2-b: 4,3-b":6,7-c"'] Trithiophene-8,12-dione Groups for High -Efficient non -fullerene Polymer Solar Cells

We synthesized a new acceptor unit anthra[1,2-b: 4,3-b': 6,7-c'']trithiophene-8,12-dione (А3Т) (A2) and then used it to design D-A₁ -D-A₂ medium bandgap donor copolymers with same thiophene (D) and A2 units but different A1 i.e., fluorinated benzothiadiazole (F-BTz) and benzothiadiazole (BTz) denoted as P130 and P131, respectively. Their detailed optical and electrochemical properties were examined. The copolymers show good solubility in common organic solvents, broad absorption in the visible spectral region from 300 nm to 700 nm, and deeper HOMO levels of -5.45 and -5.34 eV for P130 and P131, respectively. Finally, an optimized polymer solar cell based on P131 as the donor and narrow bandgap non-fullerene small molecule acceptor Y6 demonstrated a PCE of more than 11.13%. To further improve the efficiency of the non-fullerene PSC, we optimized the P130 by introducing a fluorine atom into the BTz unit, F-BTz acceptor unit, PCE PSC based on P130: Y6 active layer increased to more than 15.28 %, which is higher than that for non-fluorinated analog P131:Y6. The increase in the PCE for former PSC is attributed to the more crystalline nature and compact π-π stacking distance, leading to more balanced charge transport and reduced charge recombination. These remarkable results demonstrate that A3T-based copolymer P130 with F-BTz as the second acceptor is a promising donor material for high-performance PSCs. This article is protected by copyright. All rights reserved.

Synergistic Engineering of Substituents and Backbones on Donor Polymers: Toward Terpolymer Design of High-Performance Polymer Solar Cells

Design of terpolymers via copolymerization has emerged as a potential strategy for expanding the family of high-performing donor polymers and boosting the photovoltaic performance of non-fullerene polymer solar cells (PSCs). Herein, double-ester-substituted thiophenes and thienothiophenes are incorporated as third building blocks into the donor polymer PBDB-TF, developing two groups of terpolymers with donor-acceptor 1-donor-acceptor 2 (D-A1-D-A2)-type backbones. An optimum 10% concentration of double-ester-substituted thiophene units in PBDB-TF-T10 downshifts the molecular energy and increases the dielectric constant, and delivers proper miscibility and nanostructure in blends with the high-performing acceptor Y6. These characteristics are designed to synergistically enhance the photovoltage, photocurrent, and efficiency of PSCs. The resulting power conversion efficiency (PCE) of 16.4% surpasses the conventional PBDB-TF/Y6 PSCs, and it is among the best-performing PSCs based on PBDB-TF-derived terpolymers. Gratifyingly, PBDB-TF-T10 does not show significant batch-to-batch variation and it retains high PCEs above 16% in a broad range of molecular weights. This work introduces a facile strategy to easily synthesize terpolymers in combination with Y6 for the attainment of high-performing and reproducible non-fullerene PSCs.

Modification of NFA-Conjugated Bridges with Symmetric Structures for High-Efficiency Non-Fullerene PSCs

As electron acceptors, non-fullerene molecules can overcome the shortcomings of fullerenes and their derivatives (such as high cost, poor co-solubility, and weak light absorption). The photoelectric properties of two potential non-fullerene polymer solar cells (PSCs) PBDB-T:IF-TN (PB:IF) and PBDB-T:IDT-TN (PB:IDT) are studied by density functional theory (DFT) and time-dependent DFT (TD-DFT). Based on the optimized structure of the ground state, the effects of the electron donor (D) and electron acceptor (A) (D/A) interfaces PBDB-T/IF-TN (PB/IF) and PBDB-T/IDT-TN (PB/IDT) are studied by a quantum-chemical method (QM) and Marcus theory. Firstly, for two non-fullerene acceptors (NFAs) IF-TN and IDT-TN, the NFA IDT-TN has better optical absorption ability and better electron transport ability than IF-TN. Secondly, for the D/A interfaces PB/IF and PB/IDT, they both have high optical absorption and electron transfer abilities, and PB/IDT has better optical absorption and lower exciton binding energy. Finally, some important parameters (open-circuit voltage, voltage loss, fill factor, and power conversion efficiency) are calculated and simulated by establishing the theoretical model. From the above analysis, the results show that the non-fullerene PSC PB:IDT has better photoelectric characteristics than PB:IF.

High-Performance Non-Fullerene Polymer Solar Cells Based on a Pair of Donor-Acceptor Materials with Complementary Absorption Properties

A 7.3% efficiency non-fullerene polymer solar cell is realized by combining a large-bandgap polymer PffT2-FTAZ-2DT with a small-bandgap acceptor IEIC. The complementary absorption of donor polymer and small-molecule acceptor is responsible for the high-performance of the solar-cell device. This work provides important guidance to improve the performance of non-fullerene polymer solar cells.