Modulating Coplanarity of Polymer Acceptor Facilitates Hierarchical All-Polymer Heterojunction for Efficient and...

All-polymer-based semitransparent organic solar cells (ST-OSCs) are better-suited candidates than small-molecule analogues for building-integrated photovoltaics due to their superior operational stability. Their deployment is however hindered by low light utilization efficiency (LUE), mainly ascribed to intimating morphological control within bulk-heterojunction architectures. To mitigate these constraints, here we synergize the polymer donor-layer thinning strategy with a novel star-shaped polymer acceptor in a quasi-planar heterojunction (QPHJ) structure. Two such acceptors, PYBSe-B and PYBSe-L, are designed and synthesized with twisted π-backbones based on a sterically hindered BTSe core flanked with tailorable side-chains to regulate molecular planarity and self-aggregation behavior. By inclusion into the bottom layer of PM6 donor in QPHJs, the relatively planar PYBSe-L is aggregated between the PM6 domains whereas the amorphous PYBSe-B is well-mixed. PYBSe-L is found to expand interdomain spacing and promote infiltration of the upper PYIT acceptor, strengthening optical transmittance and exciton dissociation. The champion devices achieved an efficiency of 11.16% and a record LUE of 4.80% for all-polymer ST-OSCs. Remarkably, the rigid hierarchical polymer-infiltration network formed by the QPHJ structure greatly reinforced storage stability of the unencapsulated device with an extrapolated T₈₀ lifetime (degradation to 80% of initial LUE values) of over 1310 h under ambient conditions.