Study On The Structure-property Relationship Of Self N-doped Fullerene Ammonium

Polymer solar cells have attracted extensive attentions due to their light weight, foldable and simple production process. Recently, the development of new cathode interlayer materials is the hotspot. Fullerene derivatives could be ideal cathode interlayer materials in considering their n-type semiconductor character, higher electron mobility, and improving the interface contact. Self n-doped stable and highly conductive fullerene ammoniums with excellent thickness-tolerance could act as promising cathode interlayers to facilitate electron transfer and improve power conversion efficiencies (PCEs) of large-area PSCs. Based on the previous research, this paper studied on the structure-property relationship of fullerene ammonium iodide(PCBANI) and illuminated the cross self n-doping mechanism. Two aspects are mainly included as below:1. We performed systematic studies on the electronic and spatial structure of the fullerene core, iodide dopant and the function of the side-chain of the model compound-fullerene ammonium iodide(PCBANI) to elucidate the mechanism of the so-called "cross self n-doping" with comprehensive methods, shch as XPS, NMR, electrochemical analysis, computational modeling. This doping process forms strong anion-n interactions between iodides and fullerene cores accompanied with side-chain's head-to-tail cation-? interactions that contribute to the stabilization of the n-doped fullerene. The high conductivity related with increased electron mobility of PCBANI could be attributed to delocalization of valence electrons of iodides to fullerene cores. Moreover, two possible pathways of the cross self n-doping involving intermolecular exchange and transfer of iodide have been verified by experiment combined with computational modeling. On this basis, the electron transfer model of PCBANI was amended.2. Based on the study of PCBANI, the other two halogen ions (Br-and Cl-) were exchanged and two analogs (PCBANBr and PCBANC1) were prepared. Using ESR, XPS, NMR and other experimental methods, preliminary study of structure-property relationship of fullerene ammonium salt with different anions was explored. Experimental results showed they have similar n-doping effects and spatial structure with PCBANI.The research work provides a strategy for electrically doping and assembling of fullerenes to improve their performance in photovoltaic devices and endow them with new functionalities that could be applied to optoelectronics and organic electronics.