Enhancing the photovoltaic performance of polymer solar cells by manipulating photoactive/metal interface

In this work, a hybrid system composed of inorganic zinc oxide nanocrystals (ZnO NCs) and the organic conjugated polymer (poly[(9,9-bis(3-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)]) (PFN) was utilized as an electron selective interlayer (ESIL) to improve the electro-optical characteristics of bulk-heterojunction (BHJ) polymer solar cells (PSCs). To accomplish, water/alcohol-soluble cationic polyelectrolyte, PFN, was introduced into ZnO NCs (ZnO-PFN), aiming to enhance the electron extraction capability between the photoactive layer and the metal (Al) electrode in standard geometry BHJ PSCs. Importantly, the ZnO-PFN blend system achieved a higher power conversion efficiency (PCE) than pristine (ZnO NCs) ESILs. Moreover, an optimized photovoltaic (PV) performance was obtained with a low volume of PFN incorporated into the ZnO NCs ESIL. To validate the PV performance, PSCs were fabricated based on co-polymer of thienyl substituted BDT with TT:phenyl-C71-butyric acid methyl ester (PBDTTT-C-T:PC₇₁BM) and poly(3hexylthiophene-2,5-diyl):phenyl-C61-butyric acid methyl ester (P3HT:PC₆₁BM) photoactive systems and observed superior PV characteristics for ZnO-PFN hybrid ESILs. The optical transparency, microstructure, and morphological characteristics were evaluated using appropriate characterization techniques to demonstrate the superiority of the hybrid ZnO-PFN blend system. PSCs based on this ZnO-PFN composite based ESIL suggested an alternative practical approach to enhance the efficiency of the fabricated devices.