Fig. 1: Thickness-dependent properties of neat MPTA and MPTA/Cl6-SubPc PHJ films.

a Molecular structure of MPTA (donor) and Cl6-SubPc (acceptor). b Schematic of PHJ device architecture with varying acceptor thickness. c Normalized UV-Vis absorption spectra and (d) Absolute photoluminescence spectra (measured with 514 nm excitation and normalised to matched densities of absorbed photons). e Ambient photoemission spectra and (f) HOMO levels for neat MPTA and Cl6-SubPc as well as PHJ films with different thicknesses of Cl6-SubPc.