Investigation of Interface Properties for ClAlPc/C60 Heterojunction-Based Inverted Organic Solar Cell

The interface properties of organic donor–acceptor heterojunction comprising chloroaluminium phthalocyanine (ClAlPc) and C60 in an inverted organic solar cell configuration have been investigated, with particular emphasis on the molecular orientation and interfacial energy level alignment through the combination of in situ near-edge X-ray absorption fine structure (NEXAFS) and ultraviolet photoelectron spectroscopy (UPS) measurements. In situ NEXAFS measurements reveal that ClAlPc molecules on C60 film on indium tin oxide (ITO) electrode adopt a lying configuration with their molecular π-plane nearly parallel to the substrate surface. Such lying configuration of ClAlPc films can facilitate the efficient charge transport in heterojunction based solar cell devices. As confirmed by in situ UPS measurements, the large ionization potential of ClAlPc leads to a large energy offset between the highest-occupied-molecular-orbital (HOMO) of ClAlPc and the lowest-unoccupied-molecular-orbital (LUMO) of C60 at the ClA...