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

• To solve the solvent orthogonal problem, buffer layers based on AOB were chemically modified on ITO through BrTMS.
• This buffer layers can efficiently lower the work function of the ITO, and greatly improve the performance of PSCs.
• After insertion of this interlayer, the PCE of PSCs based on PBDTTT-C-T:PCBM was enhanced from 4.10% to 7.56%.

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.

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