A multifunctional strategy to improve the efficiency and stability of organic solar cells via a 2PACz/MA composite hole transport layer†

In the field of organic solar cells (OSCs), interfacial engineering is recognized as essential for improving power conversion efficiency (PCE). While self-assembled monolayers (SAMs) as hole transport layers (HTLs) have shown great potential, their uneven surface coverage and electrical contact on rough substrates have limited their effectiveness. In response to these challenges, we propose a [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz)/myristic acid (MA) composite HTL strategy. The introduction of MA, which has a long hydrophobic alkyl chain, improves the compatibility of the HTL with hydrophobic active layers and effectively fills the defects left by the 2PACz layer with the carboxylic acid anchoring groups. This synergistic enhancement reduces non-radiative recombination at the interface, thereby facilitating efficient charge transport and extraction. OSCs fabricated using 2PACz/MA based on D18:DTC11 demonstrated an efficiency of 19.93%, compared to 19.30% for the control. Furthermore, the MA-induced hydrophobic interface also enhances the stability of OSCs and shows versatility across different active layers, as evidenced by an increase in PCE from 19.42% to 20.02% in the D18:L8-BO:BTP-eC9 ternary system. These results demonstrate a universal and effective strategy, which not only overcomes the limitations of SAMs, but also offers a novel way to improve the efficiency and stability of OSCs by optimizing interface quality.