Suppressing the Dark Current Density of Organic Photodetectors by Narrowing the Molecular Weight Distribution

Abstract

The functionality of organic photodetectors highly depends on parameters including the band distributions in the photosensitive layer. However, the optoelectronic performances of the semiconducting polymers are closely related to the molecular weight and dispersity (Đ) of polymers varying from batch to batch. Based on Flory−Huggins solution theory, we herein demonstrate the fractionation of batches of semiconducting polymers (including PTzBI-dF, PM6, and PTB7-TH) with comparable molecular weights but diverse dispersity through dissolution fractionation in a column (DFC) strategy. This approach can macroscopically and statistically tailor the energy bandwidth, significantly reducing the dark current density of organic photodetectors. The impressively lower dark current densities of 1.37 × 10 −11 A cm −2 and higher specific detectivity of 2.19 × 10 14 Jones are obtained for PTzBI-dF polymers with smaller Đ, superior to the original batch (with 2.12 × 10 −8 A cm −2 and 5.58 × 10 12 Jones). The improvement can be attributed to the reduced trap state density, an increased band-to-band channel gap, and a higher injection potential barrier. These results demonstrate new possibilities for further performance improvement of organic photodetectors and show a cost-effective way for high-performance photoactive donor polymers to overcome batch-to-batch variations.