Low-cost synthesis of small molecule acceptors makes polymer solar cells commercially viable

Abstract

The acceptor-donor-acceptor (A–D–A) or A–DA’D–A structured small molecule acceptors (SMAs) have triggered substantial progress for polymer solar cells (PSCs). However, the high−cost of the SMAs impedes the commercial viability of such renewable energy, as their synthesis via the classical pyridine-catalyzed Knoevenagel condensation usually suffers from low reaction efficiency and tedious purifying work-up. Herein, we developed a simple and cheap boron trifluoride etherate-catalyzed Knoevenagel condensation for addressing this challenge, and found that the coupling of the aldehyde-terminated D unit and the A-end groups could be quantitatively finished in the presence of acetic anhydride within 15 minutes at room temperature. Compared with the conventional method, the high reaction efficiency of our method is related to the germinal diacetate pathway that is thermodynamically favorable to give the final products. For those high performing SMAs (such as ITIC-4F and Y6), the cost could be reduced by 50% compared with conventional preparation. In addition to the application in PSCs, our synthetic approach provides a facile and low-cost access to a wide range of D–A organic semiconductors for emerging technologies.

Tethered Small‐Molecule Acceptors Simultaneously Enhance the Efficiency and Stability of Polymer Solar Cells

“…Followed by a Vilsmeier–Haack reaction using dry N , N ‐dimethylformamide (DMF) and POCl 3 , aldehyde‐based compound 3 was obtained. Notably, the desired dimers can be nearly quantitatively obtained via our newly developed BF 3 ∙OEt 2 ‐catalyzed Knoevenagel condensation [ 44 ] from compound 3. With the flexible alkyl side chains to tether the SMAs, it can bring excellent solubility in organic solvents for device processing, which is different from the aromatic linkers in PSMAs and SMAs.…”

Asymmetric nonfullerene acceptors with isomeric trifluorobenzene-substitution for high-performance organic solar cells

“…First, an isomeric mixture of Br-IC was crystallized from different solvents to afford IC-β-Br ( 2 ) and IC-γ-Br ( 3 ), following a method described by He. 55 The two isomeric terminals, IC-β-Ar3F ( 4 ) and IC-γ-Ar3F ( 5 ), were obtained through a Suzuki coupling reaction with the brominated IC terminal-end group (compound 2 and 3 ) using Pd(dppf)Cl 2 as the catalyst, which was subsequently mixed with fluorinated IC (F-IC) to carry out the Lewis-acid catalyzed Knoevenagel condensation 56 with the aromatic-core-based mono-aldehyde (compound 6 , obtained according to a previous report 57 ) to produce the target NFAs. Compared with the classical pyridine-catalyzed method, the new approach provides facile access to NFAs with easier work-up.…”

Side chain isomerization enables high efficiency and thickness tolerant organic solar cells

“…As one of the promising photovoltaic technologies for addressing energy and environmental issues, organic solar cells (OSCs) have the characteristics of low cost, flexibility, lightweightness, environmental friendliness, large-area printing manufacture, etc. 1–5 To date, the power conversion efficiency (PCE) of OSCs has reached remarkable values exceeding 19% owing to the invention of new active layer materials, especially non-fullerene acceptors (NFAs) with acceptor–donor–acceptor (A–D–A) architectures 6–13 and efficient morphology control 14–18 for device fabrication and optimization. In the past decade, side chain engineering has proven to be an efficient method for the delicate design of active layer materials and precise regulation of the corresponding morphology because solubility, 19,20 crystallization 21 and packing modes, 22,23 etc.…”