Three-Dimensional Spirothienoquinoline-Based Small Molecules for Organic Photovoltaic and Organic Resistive Memory Applications

A new electron-rich spirothienoquinoline
unit, tBuSAF-Th, has been developed via
incorporation of a thienyl unit instead of a phenyl unit into the
six-membered ring of the spiroacridine (SAF) and utilized for the
first time as a building block for constructing small-molecule electron
donors in organic solar cells (OSCs) and as active layers in organic
resistive memory devices. The resulting three-dimensional spirothienoquinoline-containing 1–4 exhibit high-lying highest occupied
molecular orbital (HOMO) energy levels. By the introduction of electron-deficient
benzochalcogenodiazole linkers, with the chalcogen atoms being varied
from O to S and Se, a progressively lower lowest unoccupied molecular
orbital (LUMO) energy level has been achieved while keeping the HOMO
energy levels similar. This strategy has allowed an enhanced light-harvesting
ability without compromising open-circuit voltage (Voc) in vacuum-deposited bulk heterojunction OSCs using 1–4 as donors and C70 as the
acceptor. Good photovoltaic performances with power conversion efficiencies
(PCEs) of up to 3.86% and high short-circuit current densities (Jsc) of up to 10.84 mA cm–2 have been achieved. In addition, organic resistive memory devices
fabricated with these donor–acceptor small molecules exhibit
binary logic memory behaviors with long retention times and high on/off
current ratios. This work indicates that the spirothienoquinoline
moiety is a potential building block for constructing multifunctional
organic electronic materials.