Interface passivation and electron transport improvement of polymer solar cells through embedding a polyfluorene layer

Abstract

In this contribution, a series of conducting polyfluorenes (PF) are introduced to improve interface adhesion and boost charge extraction of the TiO₂ electron transport layer of inverted polymer solar cells (PSCs). After employing poly (9,9-dihexylfluorenyl-2,7-diyl) (PDF), poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(1,4-benzo-{2,1′,3}-thiadiazole)] (PDFBT), and poly[(4-(5-(7-methyl-9,9-dioctyl-9H-fluoren-2-yl) thiophen-2-yl)-7-(5-methylthiophen-2-yl)benzo[c][1,2,5]thiadiazole)] (PFTBT) as capping layers, interfacial coherence improvement and energy loss decrease are both achieved, facilitating charge transfer from the active layer to the TiO₂ layer. The optimized contact, enhanced electrical conductivity, and reduced internal resistance contribute to increased short-circuit current density and fill factor, leading to an enhanced power conversion efficiency (PCE) from 5.72% up to 7.97%. The employment of the PF capping TiO₂ buffer layer provides a promising approach to develop high efficiency PSCs.