Molecular Tuning of Titanium Complexes with Controllable Work Function for Efficient Organic Photovoltaics

Nonfullerene acceptors have recently emerged as promising candidates for organic photovoltaics (OPVs) owing to their superior optoelectronic properties. However, the varied lowest unoccupied molecular orbital (LUMO) levels of the acceptors pose difficulty in aligning their energy levels with existing electron transporting layers (ETLs). The authors propose here a facile design of the ETL with a tunable work function by simply varying the annealing temperature of titanium diisopropoxide bis(acetylacetonate) (TIAA) to change the molecular structure of the titanium complex. The energy level tuning is realized without changing the morphological features of the active layer, and as a result, it can enhance the charge extraction efficiency and thus ultimately the power conversion efficiency of the nonfullerene OPV. Our design will provide new important insights for achieving efficient nonfullerene OPVs.