Doping of organic semiconductors (OSCs) plays an important and growing role in organic electronics, ranging from OLEDs and OPVs to bioelectronics, and neuromorphic computing. However, unlike Si where parts per million dopant concentrations can significantly alter the conductivity, doping organic semiconductors with molecular dopants requires a much higher concentration (>5%), pointing to the fundamental bottlenecks in molecular doping of OSCs. Furthermore, the conductivity of doped OSCs deviates from the linear increase with doping concentration >20% (e.g., MeO-TPD doped with F4-TCNQ), or plateaus at low doping levels (e.g., 10% for P3HT doped with F4-TCNQ). This MURI team combines expertise in synthesis (You), characterization of materials (Ginger, So, Ade), novel device concepts and engineering (So), processing and morphological characterization (Amassian, Ade), computation (Li), robotic experimentation and ML data-analytics (Amassian, Ganapathysubramanian). This integrated team will address the fundamental questions outlined above, and explore novel photoredox dopant/switchable doping that can enable photopatterning of p and n doping to fabricate OSC integrated circuits. We will implement a collaborative workflow integrating robotic experimentation and machine learning (ML) to accelerate the pace of data generation, and co-design of dopant/polymers.

In this work we will investigate superconductivity in hybrid perovskites.

This research project on development of scalable materials and processes for OPV modules is a collaboration between NC State University, Georgia Tech, the University of Colorado at Boulder, and Phillips 66. These modules can help provide light-weight portable power generation systems for a variety of DOD operations. Through the collaboration with Phillips 66 which is an industrial leader in OPV development and commercialization, we will develop the materials and processes compatible with large-scale OPV manufacturing. Team members of this project have the expertise of materials chemistry, process development, characterization, device characterization and module manufacturing. Specifically, we will focus on (i) design and synthesis of scalable donor and non-fullerene acceptor materials, (ii) development of charge extraction materials, (iii) process development compatible with roll-to-roll processing, (iv) detailed structural characterization, (v) device physics characterization and failure analysis, and (vi) incorporating the materials and processes developed under this program to be evaluated by Phillips 66 in scalable photovoltaic manufacturing. The final objective is to develop scalable materials and processes that can be used in large-scale OPV manufacturing at Phillips 66.

Organic light-emitting diodes (OLEDs) have shown a great success in display technologies and are also promising for solid-state lighting. This is because they possess the advantages of surface emission, lightweight, small form factor, and flexibility, enabling their unique applications in various portable and wearable electronics. To further promote their applications, the incorporation of nanostructures has been found to be a promising approach. On one hand, the nanostructures can be used to manipulate the emission profile for advanced applications, such as polarized emission. On the other hand, the plasmonic nanostructures can address the critical issue of the short lifetime of blue phosphorescent OLEDs (PhOLEDs) through plasmonic effect. The emission profile of normal OLEDs is unpolarized. In many applications where a polarized light source is needed, the existing technology is to add a polarizer, which not only increases the form factor, but also wastes of more than half of the energy. To address this issue, achieving polarized emission directly from OLEDs has become highly desired. However, despite a vast amount of effort devoted, the current progress is still far behind the benchmark of practical applications. For example, the main approach in the literature is to uniaxially align the electric dipole of the emitters to achieve polarized emission, which exhibits poor efficiency and low polarization ratio. Another method is to integrate a polarizer with the substrate, which filters out more than half of the light, leading to a significantly reduced efficiency. In addition, both methods impose difficulties on the manufacturing. To address these issues, we will use a facile method to fabricate devices achieving efficient polarized emission, where a periodic nanostructure and a sophisticated optical design are employed together to manipulate the outcoupling of the optical modes. Our approach not only gives good performance (high efficiency and large polarization ratio), but also is more facile to be implemented compared to the other methods. In addition to achieving polarized emission, nanostructures can also be utilized to improve the stability of PhOLEDs. It is known that the short lifetime of blue PhOLEDs is one of the main challenges in OLED based solid-state lighting. In PhOLEDs, due to the long lifetime of triplet excitons, they accumulate to a high density, which enhances triplet-triplet annihilations (TTA) and triplet-polaron annihilations (TPA), and therefore causes the device degradation. To address this issue, it is critical to promote the radiative decay rate of triplet excitons to reduce their lifetime, such that TTA and TPA can be mitigated. This can be realized through plasmonic nanostructures. To solve this problem, we will develop a new method of incorporating the plasmonic NPA with OLEDs, which is manufacturable and compatible with practical applications to enhance the device lifetime.

Transparent organic solar cells (TOSCs) have revolutionized the field of photovoltaics due to their unique characteristics and have attracted attention due to their potential for integration into greenhouse windows, powered fish farm, and automobile windshields (Figure 1). The potential market size is increasing in recent years.[1] When compared with traditional silicon-based solar cells, organic solar cells are considered as a promising technology because they have many attractive merits, such as low cost, rapid energy payback time, light weight, flexibility, and more importantly, transparency.[2,3] Conventional crystalline silicon transparent solar cells are opaque. In contrast, OSCs can be made transparent by using transparent electrodes and ultrathin films of organic materials, a good transparency throughout the visible spectrum. Furthermore, they provide a much broader range of colors and luminosity by tuning the transmission spectrum.

The general project concept investigates the utilization of triplet-triplet annihilation (TTA, also known as triplet fusion) to generate blue photoluminescence emission in next generation organic light-emitting diodes (OLEDs) that would achieve unprecedented operational lifetimes and stability. To date, we have prepared several new blue emitter molecules and electron/hole transport materials along with large numbers of blue-emitting device structures featuring operational characteristics that exclusively function through the triplet fusion phenomenon. The proposed work seeks to further this research into blue emitting materials while demonstrating full color displays operating using the same principles.

The objective of this project is to achieve polarized emission from an OLED. One approach is to mechanically align the emitting molecules, resulting in polarized emission from the device. Alternatively, a fine metallic grating is used as an external polarizer to selectively transmit the TM light and reflect the TE light. However, these approaches are not practical. Uniaxial alignment inevitably induces contamination to the emission layer and damages to the devices, and the metallic grating wastes the TE light and reduces the outcoupling efficiency by half. Another way is to make emitters with an oriented emitting dipole and various attempts have been made to make these devices. However, the efficiency of these devices is extremely low and they are not practical for display applications. Therefore, having a light source intrinsically emitting polarized light can improve the device brightness and maintain the OLED thin film optical design.

The objectives of this project start with the design and synthesis of a set of stable donor polymers and stable NFAs, yielding efficiencies close to those of the state-of-the-art devices. We will study the fundamental physics and chemistry of these donor-acceptor molecular systems with the goal of establishing a set of chemical design rules for stable bulk BHJ blends. Our goal is to understand at the molecular level how donor and acceptor chemistry affects the interfacial stability and the morphological stability of the blends. With the fundamental understanding of degradation mechanisms and the knowledge of how to control them, we will further enhance the stability of OPV cells using donor polymers and molecular acceptors with a high scalability and high reproducibility. Through careful modifications of the polymer donor and acceptor chemistry to control the chemical purity, planarity, side-groups, crystallinity and miscibility, along with detailed chemical, structural and photophysical characterizations, our final objective is to determine a set of chemistry design rules to determine: (i) the criteria for stable donor polymers and acceptor molecules, (ii) the chemical factors affecting the interface and morphological stability, and (iii) the criteria for obtaining a stable blend given a stable polymer donor and a stable acceptor.

In recent years, near-eye displays such as virtual reality (VR) and augmented reality (AR) have gained great momentum in commercialization. Despite the fast progress, VR displays are often bulky and heavy due to the light collimating refractive lenses (Fig. 1). In contrast, AR displays use micro-displays and waveguide optical components to project the images which leads to a smaller form factor. However, the throughput from the input-output diffractive/holographic components are only 10%, resulting in an overall outcoupling efficiency less than 2%. One way to improve both AR and VR displays is to use image sources with directional light emission. This eliminates the need for light collimator or optical combiners, thus reducing the display size while improving the outcoupling efficiency.

Almost 40% of the light is trapped in an organic light emitting diode (OLED) as wave-guided modes as well as surface plasmon polariton (SPP) modes, and corrugated substrates are effective to extract them. Specifically, random corrugated structures are ideal for lighting because the extracted light profile will be independent of wavelength and angle. From the results of our currently funded program, we conclude that an ideal corrugated structure for light extraction should have an optimized corrugated depth at the metal electrode interface to extract SPP modes and a large refractive contrast at the transparent electrode interface to extract waveguided modes. To realize manufacturable high efficiency OLEDs for general lighting, we will fabricate white OLEDs on random corrugated substrates having an optimized nanostructure and a large index contrast at the ITO interface. Our program objective is three-fold. First, we will develop a process to produce corrugated substrates which is compatible with large volume manufacturing. Second, we will fabricate OLEDs on random corrugated substrates with a large index contrast at the ITO/substrate interface (����������������n ��������������� 0.7) to extract the light lost to the SPP modes and with an optimized corrugated depth to extract light lost to waveguided modes. Third, we will collaborate with OLED Works to validate the resulting devices developed from this R&D project. The results from our current DOE project shows that the EQE of our corrugated green OLEDs is close to 70%. By incorporating a low index buffer layer on top of a random corrugated glass substrate to enhance the refractive index contrast, our preliminary results show that an EQE of 75% is an achievable target for a fully optimized white OLED at the end of our proposed program. Manufacturable substrates for high efficiency light extraction are one of the major roadblocks for OLED lighting and the success of this program will definitely accelerate its commercialization.