Pyridine End-Capped Polymer to Stabilize Organic Nanoparticle Dispersions for Solar Cell Fabrication through Reversible Pyridinium Salt Formation

Abstract

Bulk-heterojunction nanoparticle dispersions in water or alcohol can be employed as eco-friendly inks for the fabrication of organic solar cells by printing or coating. However, one major drawback is the need for stabilizing surfactants, which facilitate nanoparticle formation but later hamper device performance. When surfactant-free dispersions are formulated, a strong limitation is imposed by the dispersion concentration due to the tendency of nanoparticles to aggregate. In this work, pyridine end-capped poly­(3-hexylthiophene) (P3HT-Py) is synthesized and included as an additive for the stabilization of P3HT:indene-C60 bis-adduct (ICBA) nanoparticle dispersions. In the presence of acetic acid (AcOH), a surface-active pyridinium acetate end-capped P3HT ion pair, P3HT-PyH+AcO–, is formed which effectively stabilizes the dispersion and hence allows the formation of dispersions with smaller nanoparticle sizes and higher concentrations of up to 30 mg/mL in methanol. The dispersions exhibit an enhanced shelf-lifetime of at least 60 days at room temperature. After the deposition of light-harvesting layers from the nanoparticle dispersions, the ion-pair formation is reversed at elevated temperatures leading to regeneration of P3HT-Py and AcOH. The AcOH evaporates from the active layer, while the performance of the corresponding solar cells is not affected by the residual P3HT-Py in the devices. Enhanced nanoparticle stability is achieved with only 0.017 wt % pyridine in the P3HT/ICBA formulation.

Green‐Processed Non‐Fullerene Organic Solar Cells Based on Y‐Series Acceptors

“…Achieving high performance requires careful consideration of all these factors. [82][83][84][85][86][87][88][89][90][91][92][93][94][95] Numerous studies have been conducted on the BHJ systems of P3HT:PCBM or P3HT:ICBA, demonstrating that surfactant-free nanoparticles can lead to PCEs of around 4% in OSCs [84] However, it has been observed that other "donor-acceptor" conjugated polymers and non-fullerene acceptors cannot remain stable without surfactants, as they tend to become electrically charged and subsequently repel the nanoparticles. [96] While surfactants play a crucial role in the formation of stable nanoparticles, they also possess an insulating nature that can have negative effects on electronic properties.…”

“…Achieving high performance requires careful consideration of all these factors. [ 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 ]…”

Eco-friendly fabrication of organic solar cells: electrostatic stabilization of surfactant-free organic nanoparticle dispersions by illumination

“…Acetic acid, which was added to the non-solvent ethanol, protonated the pyridine group and then formed a floating (negatively charged) anion. 34 After nanoparticle formation and layer deposition, the process reverted back to the uncharged polymer under evaporation of acetic acid.…”

Synthesis of Crown Ether End-Capped PM6 Copolymers with Tunable Molecular Weight for Organic Solar Cells

“…40,41 Besides, compared with the backbone and side chains of conjugated copolymers, the end-capping sites generally occupied a tiny amount, and have been difficult to study the end-capping yield in depth. 23,33 It is tricky to monitor the Stille polycondensation process and control the molecular weight as demanded. 19,42 Stopping the polymerization at the right time is the most easily proposed solution to achieve suitable molecular weight 22,43 but often requires a skilled chemist to perform several careful experiments to minimize operational error.…”

“…End-capping is one of the simple but efficient ways to improve stability and device performance. ,− Classically, two-step end-capping was applied using two excessive benzene (or thiophene) derivatives to protect the two end sites (Scheme ). , Obviously, this two-step method would cost much time, which could increase the possibility of side reactions such as destannylation, debromination, and homocoupling. ,− This method will not only reduce the yield of polymerization but also lead to bad photovoltaic performance. , Besides, compared with the backbone and side chains of conjugated copolymers, the end-capping sites generally occupied a tiny amount, and have been difficult to study the end-capping yield in depth. , …”