Robust and hydrophobic interlayer material for efficient and highly stable organic solar cells

Interlayer materials play a critical role in fabricating highly stable organic solar cells (OSCs). Here, we design a cross-linkable naphtha-lene diimide (NDI) derivative to prepare a robust and hydrophobic electron transporting interlayer for OSCs. A non-polar electron donor PCy2 is elaborately selected to n -dope the crosslinked c-NDI:PCy2 film, by which the doping density of c-NDI:PCy2 is increased by five times to obtain a high conductivity of 6.51 3 10-3 S/m. Meanwhile, the strong hydrophobicity of c-NDI:PCy2 effectively protects the device against water ingress, endowing OSCs with excellent water resistance. A power conversion efficiency of 17.7% is obtained with the c-NDI:PCy2 interlayer, representing the highest value for OSCs with an inverted device architecture. Strikingly, this OSC can be used underwater. By immersing the non-encapsulated cell in water, 70% of its initial efficiency is main-tained after 1,000 h in the dark or 4 h under continuous illumination (100 mW/cm2).