Polymer solar cells have attracted attention as one of the next generation energy sources due to their mechanical flexibility, light weight, and solution processibility that allow them to be printed on large areas easily and inexpensively. However, the lifetime of polymer solar cells is too short to be applied to commercial products, and the drawback has been considered to arise from the instability of the organic materials themselves.

By categorizing components from pristine photoactive polymers based on the unimodality of molecular weight distributions in GPC, the research team was able to define the characters of individual components. By isolating trap-embedded components from the pristine polymers via a marginal solvent extraction method, they selectively obtained a trap-free, high-molecular-weight component. The resulting polymer component exhibits 40 % enhanced power conversion efficiency. In addition, the elimination of the trap-embedded fractions significantly suppressed the photoactivated trap-width broadening and led to the almost absence of burn-in loss, suggesting a promising possibility of long-term stable PSCs.

During the study, the research team also noticed that a long-standing issue, the so-called batch-to-batch variance, could originate from the random coexistence of the component PCDTBTs that might come separately from the precipitated and from the dissolved reaction products in the same reaction flask.

Prof. Lee said, “The short lifetime problem in the field of organic electronics has raised a fundamental question as to whether the limited lifetime of PSCs is inherent to the photoactive polymers and fundamentally cannot be overcome. Our research answers the question: it depends simply on the purification of the polymer materials.” “We hopefully believe the results will pave the way to commercialization of polymer solar cells and other organic based electronics that suffer from the burn-in loss or short operating lifetime,” he added.