| Natural electronics is the field that incorporates biological molecules in organic electronic devices to create inexpensive, renewable, performance-enhancing, and environmentally safe alternatives for the electronics industry. Natural DNA, for example, has been incorporated as an electron blocking layer (EBL) to improve device efficiency and luminance in organic light emitting diodes (OLED). OLEDs require a diverse set of materials with optical and electrical properties that meet the rigorous design requirements of the device. DNA, being one of the few materials in OLEDs, lays the groundwork for other natural material to be explored.;The nucleic acid bases from the DNA and the RNA (adenine, guanine, cytosine, thymine, uracil) are excellent options for the next steps in natural OLED electronics. The bases form thin films directly by thermal evaporation, unlike DNA that requires a surfactant and solution processing. The bases were shown to have a wide range of opto/electronic properties such as refractive index, dielectric constant, resistivity, and electron/hole transport making them a good candidate for OLEDs. The thin film properties and performance of the bases were explored by depositing the individual bases as the EBL and hole blocking layer (HBL) in place of conventional OLED material. It was shown that adenine and guanine performed well as EBLs, exceeding the efficiency of the baseline device (52 vs 39 cd/A), which contained non-biological material. It was also demonstrated that OLEDs with very high efficiency can be obtained using a thin layer of thymine as an EBL, resulting in a peak efficiency of 76 cd/A and a higher maximum luminance (132,000 cd/m2) than the baseline OLED (100,000 cd/m2). In the hole blocking layer, uracil performed well by transporting electrons and blocking hole transport to provide the highest emission efficiency of the bases.;The final set of experiments demonstrated that adenine increased the hole injection of gold electrodes due to the natural affinity the base has with gold, corresponding to a 4-7 x increase in luminance. Thin film gold is an attractive electrode alternative for OLEDs on plant-based cellulose substrates since it does not require high temperature annealing and has high conductivity. Gold cannot be directly evaporated on the rough cellulose substrate, therefore, a template stripping procedure was employed using epoxy to lift off the gold electrode from Si wafers, in combination with adenine as a hole injector to yield high quality and efficient OLEDs. Nucleic acid bases are a diverse set materials that result in performance-enhancing, inexpensive, and natural-based OLEDs. |
