Solvent-resistant ITO work function tuning by an acridine derivative enables high performance inverted polymer solar cells

In order to avoid an interpenetration of the buffer and the photoactive layers during preparation of polymer solar cells (PSCs), solvent-resistant buffer films were chemically modified on indium tin oxide (ITO) surface. The conjugated aromatics acridine orange base (AOB) was introduced into the films using 3-bromopropyltrimethoxysilane (BrTMS) as coupling agent. Upon ITO surface modification, the respective work functions show a significant decrease. The modified ITO substrates were implemented in inverted PSCs based on PBDTTT-C-T:PC71BM. With the modification, the power conversion efficiency (PCE) was improved significantly from 4.10% (for the inverted PSC without this buffer layer) to 7.56%. The PCE enhancement is mainly caused by the increase of the open-circuit voltage (43%). These results indicate that the solvent-resistant film is able to facilitate electron collection and transportation, thus providing a novel route to high efficient PSCs by surface engineering.