Heat transfer in photovoltaic polymers and bulk‐heterojunctions investigated by scanning photothermal deflection technique

• Published in: Nano select 2021-04, Vol.2 (4), p.768-778
• Main Authors: Chiu, Ka Lok, Ho, Johnny Ka Wai, Zhang, Chujun, Cheung, Sin Hang, Yin, Hang, Chan, Mau Hing, So, Shu Kong
• Format: Article
• Language: English
• Subjects: Carrier mobility; Commercialization; Deflection; Dynamic stability; Heat conductivity; Heat transfer; Heterojunctions; organic photovoltaics; Organic semiconductors; phonon transport; Phonons; Polymers; scanning photothermal deflection; Semiconductors; Service life assessment; Stainless steel; Stainless steels; Strategic materials; Thermal diffusivity; Thermal stability; Thin films
• ISSN: 2688-4011; 2688-4011
• DOI: 10.1002/nano.202000226

Organic semiconductors in electronic devices usually have poor thermal conduction which could trap considerable amount of heat, inducing operational instability and reducing device lifetime, limiting commercialization potential. Despite the technological essence to understand and enhance device heat‐dissipation, related studies on organic semiconductors are very limited. In this study, the authors show that the scanning photothermal deflection technique can be employed to study the thermal transport in thin films of organic photovoltaic (OPV) polymers and bulk‐heterojunctions (BHJs), with a simple empirical correction for the extrinsic experimental configuration. Phonons are identified to dominate the thermal transport due to the low carrier mobility. For OPV semiconductors, the positive correlation between the thermal diffusivity and the molecular planarity, π–π stacking and crystallinity is demonstrated. High‐performance 2D polymers such as PM6 can possess values comparable to alloys like stainless steel. In BHJs, using a polymeric acceptor can retain high thermal diffusivities compared to fullerene and ITIC acceptors, attributed to the efficient heat transfer within the polymer chains. The results offer not only a simple, highly customizable but sensitive experimental method for thermal transport in OPV systems, but also insights into the phonon dynamics and clinical investigations for thermal stability, pushing forward strategic material design. Thermal stability of organic photovoltaics relies on high thermal diffusivity which indicates promising heatrelief capability. Scanning photothermal deflection serves as a highly sensitive probe for the thermal properties. Phonon transport in semiconducting polymers is found to increase with their planarity and π–π stacking. Using polymeric acceptors in bulk‐heterojunctions can retain efficient heat transfer along the polymer chains.