{"id":1333,"date":"2013-07-25T18:27:55","date_gmt":"2013-07-25T18:27:55","guid":{"rendered":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/?p=1333"},"modified":"2013-08-05T18:41:14","modified_gmt":"2013-08-05T18:41:14","slug":"mechanical-pressure-induced-solid-state-solvation-in-organics-thin-films","status":"publish","type":"post","link":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/mechanical-pressure-induced-solid-state-solvation-in-organics-thin-films\/","title":{"rendered":"Mechanical Pressure-induced Solid State Solvation in Organics Thin Films"},"content":{"rendered":"

Significant technological progress of organic semiconducting structures has led to their commercialization in the form of organic LED displays, solid state lighting, and thin film photovoltaics. A guest:host doping system is often employed, and dicyanomethylene (DCM) class dyes are used extensively as the dopant molecules in both fundamental studies and applications[1<\/a>]<\/sup>,[2<\/a>]<\/sup>. The solvation effect describes the physical reorientation of surrounding solvent molecules due to a change in solute dipole moment during transition, affecting the excitonic energy states of the emitting solute dye molecules. This local dielectric effect has been extensively studied in liquid state[3<\/a>]<\/sup> and has been reported in molecular doping studies in solid state[4<\/a>]<\/sup>,[5<\/a>]<\/sup>. In this work we demonstrate and numerically quantify a new method of probing dielectric-dependent excitonic-energy-shifts though application of pressure. Thin films of polystyrene (PS) and Alq3<\/sub> doped with laser dye DCM(II) showed bathochromic shift in photoluminescence (PL) under increasing pressure, as shown in Figure 1. Films of 5% doped PS:DCM(II) showed peak energy shifts up to 40 meV under pressure change of 0.4 GPa, which when fitted to solid state solvation theory (Figure 2)[5<\/a>]<\/sup>,[6<\/a>]<\/sup>, suggests a PS elastic modulus of 1.2\u00b10.6 GPa. Similarly, films of 1% doped Alq3:DCM(II) under pressure showed peak energy shifts up to 50meV, suggesting an Alq3<\/sub> elastic modulus of 0.9\u00b10.4 GPa. The results demonstrate the first numerically quantified solid-state solvation effect due to pressure. This ability to tune exciton energy using an external parameter creates a novel method to explore applications such as controlling exciton diffusion and optimizing optoelectronic device.<\/p>\n\n\t\t