Carrier Transport Enhancement in Conjugated Polymers through Interfacial Self-Assembly of Solution-State Aggregates

We demonstrate that local and long-range orders of poly­(3-hexylthiophene) (P3HT) semicrystalline films can be synergistically improved by combining chemical functionalization of the substrate with solution-state disentanglement and preaggregation of P3HT in a θ solvent, leading to a very significant enhancement of the field effect carrier mobility. The preaggregation and surface functionalization effects combine to enhance the carrier mobility nearly 100-fold as compared with standard film preparation by spin-coating, and nearly 10-fold increase over the benefits of preaggregation alone. In situ quartz crystal microbalance with dissipation (QCM-D) experiments reveal enhanced deposition of preaggregates on surfaces modified with an alkyl-terminated self-assembled monolayer (SAM) in comparison to unaggregated polymer chains in the same conditions. Additional measurements reveal the combined preaggregation and surface functionalization significantly enhances local order of the conjugated polymer through planarization and extension of the conjugated backbone of the polymer which clearly translate to significant improvements of carrier transport at the semiconductor–dielectric interface in organic thin film transistors. This study points to opportunities in combining complementary routes, such as well-known preaggregation with substrate chemical functionalization, to enhance the polymer self-assembly and improve its interfacial order with benefits for transport properties

Mesostructured Fullerene Electrodes for Highly Efficient n–i–p Perovskite Solar Cells

Electron-transporting layers in today’s state-of-the-art n–i–p organohalide perovskite solar cells are almost exclusively made of metal oxides. Here, we demonstrate a novel mesostructured fullerene-based electron-transporting material (ETM) that is crystalline, hydrophobic, and cross-linked, rendering it solvent- and heat-resistant for subsequent perovskite solar cell fabrication. The fullerene ETM is shown to enhance the structural and electronic properties of the CH₃NH₃PbI₃ layer grown atop, reducing its Urbach energy from ∼26 to 21 meV, while also increasing crystallite size and improving texture. The resulting mesostructured n–i–p solar cells achieve reduced recombination, improved device-to-device variation, reduced hysteresis, and a power conversion efficiency above 15%, surpassing the performance of similar devices prepared using mesoporous TiO₂ and well above the performance of planar heterojunction devices on amorphous or crystalline [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM). This work is the first demonstration of a viable, hydrophobic, and high-performance mesostructured electron-accepting contact to work effectively in n–i–p perovskite solar cells

Increasing H‑Aggregates via Sequential Aggregation to Enhance the Hole Mobility of Printed Conjugated Polymer Films

Solid-state microstructures of conjugated polymers are essential for charge transport in electronic devices. However, precisely modulating aggregation pathways of conjugated polymers in a controlled fashion is challenging. Herein, we report a sequential aggregation approach via selectively modulating side chain aggregation in solution state and backbone aggregation during film formation to increase H-aggregates and consequently enhance hole mobility of printed diketopyrrolopyrrole-based polymer (PDPP-TVT) film. The sequential aggregation is realized by introducing 1-bromonaphthalene additive into chloroform solvent. The structural evolution and assembly pathways of PDPP-TVT in initial solution and during printing were revealed using small-angle neutron scattering, cryogenic transmission electron microscopy, and time-resolved optical diagnostics. The results show that the poor interactions between PDPP-TVT side chains and BrN triggers side chain aggregation to form large H-aggregate nuclei in initial solution. The additive further selectively forces backbone aggregation on H-aggregate nuclei during printing with dynamics increasing from ca. 3 to >1000 s. Such prolonged growth window and selective growth of H-aggregates produce large fibers in printed film and therefore 3-fold increase in hole mobility. This work not only provides a promising route toward high-mobility printed conjugated polymer films but also reveals the important relationship between assembly pathways and film microstructure

Hybrid Tandem Quantum Dot/Organic Solar Cells with Enhanced Photocurrent and Efficiency via Ink and Interlayer Engineering

Realization of colloidal quantum dot (CQD)/organic photovoltaic (OPV) tandem solar cells that integrate the strong infrared absorption of CQDs with large photovoltages of OPVs is an attractive option toward high-performing, low-cost thin-film solar cells. To date, monolithic hybrid tandem integration of CQD/OPV solar cells has been restricted due to the CQD ink’s catastrophic damage to the organic subcell, thus forcing the low-band-gap CQD to be used as a front cell. This suboptimal configuration limits the maximum achievable photocurrent in CQD/OPV hybrid tandem solar cells. In this work, we demonstrate hybrid tandem solar cells employing a low-band-gap CQD back cell on top of an organic front cell thanks to a modified CQD ink formulation and a robust interconnection layer (ICL), which together overcome the long-standing integration challenges for CQD and organic subcells. The resulting tandem architecture surpasses previously reported current densities by ∼20–25% and yields a state-of-the-art power conversion efficiency (PCE) of 9.4%