Correlating the Molecular Structure of A-DA′D-A Type Non-Fullerene Acceptors to Its Heat Transfer and Charge Transport Properties in Organic Solar Cells

Efficient heat transfer is beneficial to heat dissipation and the thermal durability of organic solar cell (OSCs). In this regard, heat transfer properties of organic semiconductors within OSCs should play important roles, but their thermal properties are rarely explored. Here, heat diffusion properties of Y-series non-fullerene acceptors processing different DA′D framework, named BZ4F-5, BZ4F-6, and BZ4F-7 are probed; it is found that backbone rings extension from five- to six- and seven-membered-fused rings trigger longer phonon mean free path and higher thermal diffusivities (D) in their pristine solid films and bulk heterojunction blends. Particularly, the correlation between the thermal transport properties in Y-series acceptors and their backbone geometry, molecule stacking, and thin-film crystallinity is demonstrated. More importantly, both organic thin-film transistors and OSCs confirm that thermal durability of organic semiconductor devices correlated with the thermal properties of their active layer. Although BZ5F-6 and BZ4F-7 based devices possess similar device performance at room temperature, superior heat dissipation in BZ4F-7 molecule endows it with enhanced device lifetime. These results contribute to critical design criteria for future molecular optimization in photovoltaic and optoelectronic devices.