Organic photovoltaics based on self-assembled rosette nanotubes and stacked graphene

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To overcome the drawbacks of inorganic solar cells, organic photovoltaics (OPVs) was introduced as a viable energy source with advantages such as cost-effectiveness, lightweight, and flexibility. However, low power conversion efficiency (PCE) is still limiting them from moving beyond the laboratory. This work focuses on developing a simple fabrication and characterization process for OPV manufacturing and addressing common issues with OPV devices. The second part of this thesis focuses on fabricating more affordable solar cells by finding alternatives for expensive indium-tin-oxide (ITO) electrode for optoelectronic applications. Herein, we employed chemical vapor deposition (CVD) to grow graphene in an inexpensive way by stacking several layers on top of each other to improve the performance of the electrode. Stacked graphene was characterized by Raman and UV-Vis spectroscopy and conductivity measurements. Solar cells fabricated with stacked graphene anode showed an enhancement of PCE as a function of the number of stacked layers. The highest efficiency was measured for the double-transferred graphene anode because of improved conductance an optimal transmittance. This work establishes that layered graphene is a viable substitute for ITO. The third part of this work is dedicated to improving the low PCE of OPVs to overcome the low PCE values. Poor PCE performance is a result of ill-defined morphology. By employing supramolecular nanoscale self-assembly, which is a potent method to impose well-defined ordering to organic materials, building blocks can form highly oriented spatial arrangements leading to higher PCE. It has previously been found that three porphyrin-functionalized guanine-cytosine (G^C) building blocks can be modified and characterized to serve as electron donors within the cell architecture. These motifs can form stable rosette nanotubes (RNTs) in solution via hierarchical self-assembly by hydrogen bonding and π-π stacking.8 Finally, solar cells were fabricated with porphyrin RNT as donor material and PCE was obtained and optimized. The efficiency of solar cells based on self-assembled motifs was up to 7 folds higher than un-assembled donor molecules. This work introduces a new strategy to employ one-dimensional and photoactive structures in the morphology to achieve higher charge mobility and boost up the efficiency for solution-processed OPVs.