Investigating the relationship between polymer growth and homocoupling defects using high-resolution STM imaging

Conjugated polymers are key materials in the field of organic semiconductors due to their excellent electrical properties, mechanical flexibility and ease of processing, making them attractive for a range of applications from optoelectronics to bioelectronics. However, structural imperfections such as homocoupling defects can influence their charge transport properties and compromise their performance. Moreover, the role these defects play in polymer growth remains poorly understood, largely due to the limitations of conventional characterization techniques in identifying and quantifying such sequence errors. Here, we combine electrospray deposition (ESD) and scanning tunneling microscopy (STM) to visualize individual polymer chains and resolve the precise backbone sequence in three structural variants of the benchmark conjugated polymer pBTTT. Through advanced statistical analysis of defect frequency and position, we investigate whether homocoupling are randomly distributed, whether defect density correlates with polymer length, and whether defects tend to accumulate at polymer chain ends. Our results show that homocoupling defects are uniformly distributed, do not preferentially occur in shorter polymers or at chain termini, and are therefore unlikely to play a limiting role in polymer growth.