Novel cross-linked films from epoxy-functionalized conjugated polymer and amine based small molecule for the interface engineering of high-efficiency inverted polymer solar cells

The modification of metal/metal oxide electrode is of great importance to the performance of inverted organic optoelectronic devices. Cross-linked films provide good chance to modify the metal/metal oxide electrode and enable the fabrication of high-performance multi-layer organic optoelectronic devices due to its superior ability to resist solvent erosion. However, most of the reported methods to prepare cross-linked films are suffering from harsh processing conditions such as high-temperature thermal treatment or long-time UV radiation. Here, we develop novel robust cross-linked thin films which are prepared from an epoxy-functionalized conjugated polymer (PFEX) and an amine-based small molecule (TAA). The cross-linking processing can be realized under mild heating due to the highly-efficient amine-epoxide reaction, and the resulting cross-linked films show good solvent resistibility. Moreover, the cross-linked films showed large tolerance with the composition of PFEX and TAA, which provides opportunity to modify the metal/metal oxide electrodes in a wide range using the cross linked films. The modified indium tin oxide (ITO) using the cross-linked films show much lowered work function and hydrophobic property than pristine ITO, which indicates great potential application in inverted organic optoelectronic devices. Inverted polymer solar cells (IPSCs) using the modified ITO show remarkable enhanced power conversion efficiency (9.4%) than those with pristine ITO (6.8%). Our design and preparation of the novel cross-linked films and the finding on the correlation between cross-linked film and photovoltaic performance will be useful to design and prepare high-performance cross-linked films for inverted organic optoelectronic devices.