Scaling Up Principles for Solution-Processed Organic Single-Crystalline Heterojunctions

Abstract

The development of advanced organic devices has already broken the limit of one-component material constitution, seeking for integration of multiple components to achieve new features. It is well-known that organic single crystals have highly ordered molecular packing, which directly bounds up with electrical and optoelectrical behaviors. Thus, organic heterojunctions composed of binary organic single crystals are able to exhibit superior electrical/optoelectrical performance as well as novel functions. Intimate junction contact, high coverage, and wellaligned morphology are demanded in large-scale organic singlecrystalline heterojunctions for realizing subsequent device fabrication and further practical production. So far, fabrication of organic single-crystalline heterostructures without destroying the single crystallinity of both crystals has been extremely challenging, due to the fragile nature of weak noncovalent molecule−molecule interactions in organic single crystals. Therefore, the long-standing discrepancy will exist between the urgent need of organic singlecrystalline heterojunctions with desired morphology and enormous challenges in feasible large-scale preparation. Along with continuous developments in recent literature, we try to provide two principle frameworks including two-step crystallization and onestep crystallization methods as possible solutions.

Single-crystal dielectrics for organic field-effect transistors

“…With the development of techniques such as blade/bar coating, it is promising to realise controllable modulation of the crystallinity and orientation of PVDF-based polymer materials. 80…”

Incorporating polymers within a single‐crystal: From heterogeneous structure to multiple functions

“…99,100 Thus, the combination of "long-range ordering" and "hetero-structure" is of significance and has attracted a lot of scientific interests. In contrast to planar heterojunctions with long-range ordering, 101,102 it is difficult to achieve long-range…”

“…Thus, the combination of “long‐range ordering” and “hetero‐structure” is of significance and has attracted a lot of scientific interests. In contrast to planar heterojunctions with long‐range ordering, 101,102 it is difficult to achieve long‐range ordering in bulk‐heterojunctions (BHJ's) with two interpenetrated phases that was commonly used in organic photoelectric conversion devices 103–105 . Instead, due to the enormous nucleation events occurred inside the conventional donor‐acceptor blends, only short‐range ordered BHJ's have been fabricated (Figure 13A), which limits the further development of photoelectric conversion devices.…”

Crystallization from a Droplet: Single-Crystalline Arrays and Heterojunctions for Organic Electronics

“…The critical benefit of the vertically stacked single-crystalline heterojunction is the intact heterointerface that helps to maintain high mobility and long exciton diffusion lengths in both the single-crystalline components. 44 In ambipolar OFET applications, it leads to the simultaneous expression of the intrinsic single-crystalline property to the largest extent. For OPV applications, the van der Waals heterointerface reduces the interdiffusion between the two OSC materials and thus interfacial energy states, which potentially lead to larger opencircuit voltage.…”

“…The critical benefit of the vertically stacked single-crystalline heterojunction is the intact heterointerface that helps to maintain high mobility and long exciton diffusion lengths in both the single-crystalline components . In ambipolar OFET applications, it leads to the simultaneous expression of the intrinsic single-crystalline property to the largest extent.…”