Temperature-dependent charge transport measurements unveil morphological insights in non-fullerene organic solar cells

The morphological analysis of bulk heterojunction (BHJ) active layer stands as a critical imperative for advancing the performance of future organic solar cells. Conventional characterization tools employed for morphological investigation often require substantial resources, both in cost and physical space, thereby imposing restraints on research endeavors in this domain. Here, we extend the application of charge carrier transport characterization beyond conventional mobility assessments, utilizing it as a table-top method for preliminary morphological screening in organic thin films. The investigation focuses on several high-performance BHJ systems that utilize typical "Y" non-fullerene acceptors. It involves in-depth transport studies, including temperature- and field-dependent transport characterizations. The resulting transport data are analyzed in detail using the Gaussian disorder model to extract key transport parameters, specifically the high-temperature limited mobility (mu(infinity)) and positional disorder (& sum;). Integrating these transport parameters with morphological insights obtained through various characterization tools-including x-ray scattering, sensitive spectroscopy, and quantum chemistry simulation-provides a deep understanding of the intricate interplay between charge transport properties and morphological characteristics. The results reveal explicit relationships, associating mu(infinity) with the degree of molecular stacking in BHJs and & sum; with the structural disorder in molecule skeleton. Our findings point to the promising potential of utilizing a simple transport characterization technique for the early stage evaluation of thin film packing and geometric properties of organic materials.