Boosting the efficiency of organic solar cells via plasmonic gold nanoparticles and thiol functionalized conjugated polymer

Conjugated polymers are promising low-cost, lightweight, and flexible candidates for scalable photovoltaic applications to establish decarbonized energy technologies. However, they possess deficiencies in terms of their lower charge mobility and exciton diffusion length compared to their inorganic counterparts, impeding the efficient charge extraction at high active layer thickness values. In this manner, active layer composition should be tuned to improve light harvesting enabling efficient charge transport. This work presents two new approaches to achieve higher photovoltaic performance for organic photovoltaic systems; thiol modification of the polymers for improved morphological features, and incorporation of ligand-free gold nanoparticles with surface plasmon absorption into the active layer to be stabilized by the covalent interaction with the thiol side groups of the polymers. To achieve this goal, a benzoxadiazole bearing polymer (POxT) and its bromine (POxT-Br) and thiol (POxT-SH) comprising derivatives were synthesized, their electrochemical, optical, photovoltaic, and morphological characterizations were performed. For photovoltaic characterizations, conventional device architecture of ITO/PEDOT:PSS/polymer:PC71BM/LiF/Al was utilized, where the POxT-SH showed the highest JSC and PCE values, 6.52 mA/cm2 and 2.71%, respectively. Gold nanoparticles were synthesized via laser ablation method, and upon incorporation, the PCE value was boosted to 3.29%, with an increase of 21.4% compared to POxT-SH comprising organic solar cells.