(257c) Controlling Structure-Property Relationships in Organic Semiconductors Using Tunable Highly-Ordered 2D Perovskite Interfaces

Organic Semiconductors (OSCs) have been extensively studied in a variety of fields such as device engineering and solid-state physics for their optical and electronic properties. OSCs are solution processable, which allows for high-throughput fabrication of lightweight, flexible devices, making them a competitive alternative to amorphous and polycrystalline silicon semiconductors. A challenge of utilizing OSCs is their natural tendency to crystallize into multiple molecular packing motifs, called polymorphs, which yield highly variable charge transport capabilities and optoelectronic properties. Also affected is the property of singlet fission, an exciton multiplication process in which one absorbed photon is converted into two triplet excitons. This sharing of energy from one photon to two triplet excitons could result in quantum efficiencies greater than 100% providing an opportunity to surpass the Shockley-Quisser limit and lead to the creation of higher efficiency solar cells.

In this work, two-dimensional (2D) lead halide perovskites were utilized as a highly ordered self-assembled monolayer (SAM) with tunable ligand density and variable ligands, in which six interface-stabilized polymorphs of a small molecule OSC, namely TIPS-pentacene were isolated via meniscus guided coating and subsequent thin film relaxation in-order to release strain. These interface-stabilized polymorphs were identified using grazing incidence x-ray diffraction, where incremental changes in the (101) plane spacing were elucidated, having a small range of 0.12Å. Distinct bandgap transition energies and relative deviations in steady-state photoluminescence were discerned, indicating varying degrees of intermolecular interactions arising from the unique crystal structures. Through our work, we study the effect of crystal structure on singlet fission without introducing the effects of crystal morphology, altering the polymorph, or relying on metastable structures. Singlet fission rates were enhanced due to the increased order and control of TIPS-pentacene molecular packing as a result of creating an interface-stabilized structure. This demonstrates that for singlet fission, long-range molecular coherence has a significant impact on the resulting rate. This work motivates the use of a variety of combinations of 2D lead halide perovskites and small molecule organic semiconductors to optimize and control structure-property relationships utilizing interface engineering.