Epitaxial crystallization of isotactic polystyrene (iPS) on the oriented isotactic polypropylene (iPP) substrate and the reverse process, that is, epitaxial growth of iPP crystals on the oriented iPS film initially generated by epitaxy of it on iPP, have been investigated through transmission electron and atomic force microscopies. Epitaxy of iPS on the ordered iPP substrate was achieved by cold crystallization of an amorphous thin film at 130 °C for 2 h. The results indicate that epitaxy of iPS on the iPP substrate has parallel chain relationship. Epitaxial growth of iPP on the oriented iPS film was realized by selective melting of the iPP in the epitaxial iPP/iPS system at 190 °C for 5 min and then crystallizing at varied temperatures. It was found that oriented recrystallization of iPP on the itself-induced iPS epitaxially oriented substrate occurs at temperatures below 30 °C and produces exactly the same parallel mutual chain alignment, indicating the reversibility of epitaxy between iPP and iPS. It does, however, not happen at temperatures over 60 °C, reflecting a temperature-dependent epitaxial growth of iPP on iPS oriented films. This was explained by secondary nucleation and indicates that a larger dimension of substrate crystals than the depositing epitaxial ones is necessary for the occurrence of polymer epitaxy. This provides a theoretical basis for the substrate selection of polymer epitaxies.

Zinc oxide (ZnO) is a widely used cathode interlayer material in inverted organic solar cells (OSCs). However, there are lots of surfaces or bulk film defects in ZnO layers, which degrade solar cell performance. Here, the typical phosphorylcholine-and sulfobetaine-based polymer zwitterions (PMPC and PDMAPS) are synthesized via reversible addition-fragmentation chain-transfer (RAFT) polymerization to modify ZnO interlayers for inverted OSCs. The polymer zwitterions can efficiently passivate the defects in ZnO films and thus increase the conductivity of the ZnO interlayers. Both PMPC and PDMAPS modified ZnO interlayers show some general advantages in improving the performance of fullerene-based and non-fullerene-based OSCs. The highest efficiency of 16.69% is achieved by using PMPC modified ZnO interlayers in PM6:Y6 based solar cell devices, which is among the best performance in inverted OSCs. Such an improvement in device performance is attributed to the work function reduction of the polymer zwitterions modified ZnO films, which provides an efficient cathode platform to extract and transport electrons from the active layers, to the benefit of suppressing interfacial charge recombination. As a result, the organic-inorganic hybrid composites (ZnO: polymer zwitterions) show efficient interfacial modification to align energy levels at the device interface, which have promising application prospects in organic electronics.