Understanding Transition Dipole Moment Orientation in Thin Films via Fourier Imaging Microscopy

The precise control of transition dipole moment (TDM) orientation is a critical factor in optimizing the performance of optoelectronic devices. We employ Fourier-plane imaging microscopy (FIM) to investigate the orientation of TDMs in solution-processable nanomaterials, with a particular focus on thin films used in organic light-emitting diodes (OLEDs), quantum dot LEDs, and other photonic devices. By capturing angular emission profiles, FIM provides high-precision, nondestructive analysis of the TDM alignment within the thin film layers, revealing key insights into the device physics.

This technique is shown to be effective across a wide range of materials, including organic emissive layers, hybrid organic-inorganic films, and quantum dots, where the alignment of TDMs directly impacts light outcoupling efficiency and angular emission profile. Additionally, FIM allows for detailed morphological investigations, crucial for understanding the effects of thin film processing on molecular orientation and phase behavior. Our findings highlight how FIM can serve as a powerful tool not only for enhancing the performance of light-emitting devices but also for probing the physics of various optoelectronic devices.

The results presented demonstrate the versatility of FIM in improving various optoelectronic applications. For example, in organic or quantum dot LEDs, proper TDM alignment enables significantly brighter emission by increasing photon outcoupling efficiency. Furthermore, the ability to map the morphology of organic thin films at the nanoscale provides critical information for optimizing device structures such as thermal stability of a device. In addition, the method enables unveiling the detailed physical interactions within hybrid heterojunctions.
In summary, Fourier-plane imaging microscopy offers a comprehensive method for characterizing and optimizing the TDM orientation and overall morphology in thin films, which is applicable to a wide range of optoelectronic devices. This work provides a foundation for further exploration of emerging solution-processable nanomaterials, presenting new pathways for improving the performance and functionality of devices across fields.