Electroactive and Self-healing Polyurethane Doped Tin Oxide Interlayers for Efficient Organic Solar Cells†

Abstract

Tin oxide (SnO₂) has been widely used as an electron transport layer (ETL) in optoelectronic devices. However, there are numerous surface or bulk defects in SnO₂, working as charge recombination centers to degrade device. Here, an electroactive and self-healing polyurethane (PHNN) was designed by integrating conjugated unit – naphthalene diimide (NDI) into a typical polyurethane backbone. Numerous hydrogen bonds and π interactions in PHNN work as non-covalent interactions to endow this polymer with superior self-healing properties. PHNN contains lots of aliphatic amine and carbonyl groups, which effectively passivate the defects in SnO₂. The π stacking of NDI units will facilitate electron delocalization, endowing PHNN with electrical activity compared with traditional polyurethane. Doping SnO₂ with PHNN can improve the conductivity and reduce the work function of SnO₂ layer, which is conducive to efficient charge extraction and transport. Using PHNN doped SnO₂ as ETL for PM6: Y6 and PM6: BTP-eC9 based inverted organic solar cells can achieve a high efficiency of 17.16% and 17.51%, respectively. Devices containing doped SnO₂ ETL show significantly improved efficiency and stability. Thus, the electroactive polyurethane doped SnO₂ interlayers show high performance interfacial modification to align energy-levels in solar cell devices, which have promising applications in organic electronics.