Russell J. Holmes, University of Minnesota, Minneapolis, MN
Displays based on organic light-emitting devices (OLEDs) are increasingly ubiquitous for mobile and wearable applications, with increasing growth in augmented/virtual reality and lighting. High performance is enabled in part by processing using high vacuum thermal evaporation (VTE), offering high uniformity and compositional control. However, vapor processing also offers a finer level of property optimization in terms of control over molecular orientation. While the films used in OLEDs are generally amorphous, their electrical and optical performance is still subject to the average molecular orientational in thin film, a parameter that can be manipulated through choice of processing conditions. In parallel, there is increasing interest in applying vapor processing for the fabrication of metal-halide perovskite thin films and devices. Perovskites are among the most promising active materials for the realization of efficient, low-cost, photovoltaic modules. These often hybrid organic-inorganic materials present unique challenges for vapor processing, in part due to the need to controllable vaporize organo-halide compounds. This talk will center around two primary focus areas. First, we will examine recent efforts to engineer organic semiconductor thin film behavior and OLED performance through choice of processing conditions that tune average molecular orientation. Specific interest is in how preferred molecular orientation impacts thin film birefringence, optical outcoupling efficiency, peak device efficiency, and device degradation. Second, we will discuss the application of vapor transport deposition (VTD) to the processing of hybrid organic-inorganic perovskites, and the impact on subsequent application of these films in photovoltaic cells. This talk will conclude with a discussion of how vapor processing of these materials opens new axes for engineering behavior, and future opportunities for advances in vapor processing of both materials classes.