15.28% efficiency of conventional layer-by-layer all-polymer solar cells superior to bulk heterojunction or inverted cells

Series of conventional and inverted all-polymer solar cells (APSCs) were prepared with polymer PM6 as donor and polymer PYF-T-o as acceptor based on layer-by-layer (LbL) or bulk heterojunction (BHJ) structure. The power conversion efficiency (PCE) of 15.28% and 14.97% can be achieved in conventional LbL and BHJ APSCs, respectively. The relatively high PCE of conventional LbL APSCs is mainly originated from short circuit current density (J_SC) improvement caused by optimized phase separation and more ordered molecular arrangement for efficient charge extraction and transport in layered active layers. Meanwhile, the efficient energy transfer from PM6 to PYF-T-o should provide an additional exciton utilization channel, which is also responsible for relatively high performance in conventional LbL APSCs. It is worth noting that the inverted APSCs exhibit low PCE as compared to that of corresponding conventional APSCs, especially for the inverted LbL APSCs with only 8.54% PCE. The markedly inferior PCE in inverted LbL APSCs is mainly attributed to the insufficient PYF-T-o exciton dissociation, which can be demonstrated from the greatly low EQE spectra in long wavelength region as compared to that of other type APSCs. This work provides more deep insight on the dynamic process in LbL active layers, which should contribute to the construction of highly efficient APSCs based on LbL processing method.