Investigating the effect of diverse structural variation of conjugated polymer electrolytes as the interlayer on photovoltaic properties

Abstract

The effect of the diverse structural variation of conjugated polymer electrolytes (CPEs) as an interlayer on the photovoltaic properties was investigated. We found that the CPE with a strong electronegative BT group in the backbone and OH salt group in the side chain offers the highest PCEs among CPEs. • Diverse structural variation of conjugated polymer electrolytes (CPEs). • Step-by-step improvement in efficiency of solar cells based on diverse CPEs as interlayer. • Optical simulations of solar cells using transfer matrix formalism. A series of conjugated polymer electrolytes (CPEs) based on dimethylamino propyl fluorene (FN), thiophene (T), benzothiadiazole (BT), and dithienyl benzothiadiazole (TBT) were synthesized by the Suzuki coupling reaction. Quaternarized polyelectrolytes were obtained from the post-polymerization treatment of the amino-terminal group. The incorporation of electron-rich (T), electron-deficient moiety (BT), and their combination (TBT) in the polymer backbone represent the different effects of polarity. Conjugated backbones are substantially strengthened by varying their electron affinity and conjugated planarity. We systematically investigated the effect of applying CPEs with different backbones and functionalities in the side chain. Different backbones produce different molecular dipoles, and the side chain functionality induces an interfacial dipole. Inverted polymer solar cells (iPSCs) based on a bulk heterojunction (BHJ) were fabricated with the ITO/ZnO/CPE/PTB7-Th:PC 71 BM/MoO 3 /Ag structure. The device performance enhancement was achieved by inserting CPEs as the interlayer. Modifying the polymer backbone leads to improved efficiency and modifying the side chain functionality improves the performance compared with that of the interlayered neutral polymer.