Marcus D. Cole
Integration of well-designed interfaceal layers into photovoltaic devices is crucial for optimizing power conversion efficiency (PCE) and device stability. Interfacial layers improve device performance through several mechanisms, including work function modification of metal electrodes, promoting energy level-alignment within multi-layer devices, and enhancing charge injection at metal electrodes. This poster will describe the synthesis and characterization of main-chain polymer electrolytes, known as polyionenes, as well as polymer zwitterions containing perylene diimide (PDI) moieties in the polymer backbone. Starting from PDI-based monomers, containing tertiary amines at the imide positions, and solubilizing groups at the 1 and 7 positions of the perylene core, a new class of n-type polymers was prepared. PDI incorporation into the polymer backbone was modulated by the monomer feed ratio and the solution properties of these polymers were investigated by UV-vis and photoluminescence spectroscopy in both aqueous and alcoholic media. The utility of these PDI-based polymers as electron-transporting layers was assessed via ultraviolet photoelectron spectroscopy (UPS). The PDI-containing polyelectrolytes were employed as electron-transporting layers in bulk heterojunction (BHJ) photovoltaic devices. Device performance and thin film morphology were studied as a function of PDI content. Through this study, an ideal “conjugation density” of 50 mole percent PDI was identified as providing optimum thickness tolerance of the interlayers and performance of the resultant solar cells. The polyionene platform affords a unique opportunity to modulate conjugation and charge density within the polymers and examine their relationship to interfacial dipole at metal interfaces and electron-transporting properties.