An alcohol-soluble small molecule as efficient cathode interfacial layer materials for polymer solar cells

Interface modification makes an important contribution to improving the optoelectronic performance and stability of polymer solar cells (PSCs). Here, the hexamethylenetetramine (C6H12N4) was successfully introduced into PSCs as cathode interface layers (CILs) using environmental-friendly methanol as solvent. Compared to the PSCs without CILs, the open circuit voltage (VOC) and short-circuit current density (JSC) of the device with C6H12N4 CILs was increased from 0.44 V to 12.73 mA cm−2 to 0.77 V and 15.89 mA cm−2, respectively. More importantly, under the same experimental conditions, the optimal power conversion efficiency (PCE) of the device with C6H12N4 CILs was improved to 7.79%, which is 185% higher than that of the device without C6H12N4 CILs (2.73%). We found that the active layer PTB7-Th:PC71BM showed a smoother interface morphology and better hydrophilicity after insertion of CILs, which facilitated enhance the physical contact between active layers and cathode as well as electron extraction and transport. The results show that the introduction of C6H12N4 as CILs provides an effective method for preparing high-performance PSCs. •C6H12N4 has been successfully exploited in PSCs as electron transfer layer.•C6H12N4 can reduce cathode work function and efficiently extract electrons.•C6H12N4 modifies the active layer to exhibit a smoother interfacial topography, which reduces contact resistance of PSCs.