Sulfur-doped molybdenum oxide anode interface layer for organic solar cell application.

Efficient organic solar cells (OSCs) based on regioregular of poly (3-hexylthiophene):fullerene derivative [6,6]-phenyl-C61butyric acid methyl ester composites have been fabricated on indium tin oxide (ITO) coated glass substrates by using a sputtered sulfur-doped molybdenum oxide (S-MoO3) film as anode interface layer (AIL). With the help of X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy, we find that oxygen flow ratio control can modulate the amount of sulfur doping into MoO3, then further tune the Mo(+4)/Mo(+5)/Mo(+6) composition ratios, Fermi level, electron affinity, valence band ionization energy and band gap of MoO3. A partially occupied Mo 4d-bands of Mo(5+) and Mo(4+) states modulated by sulfur doping are the main factor which influences the valence electronic structure of S-MoO3.These orbitals overlap interrelation push the valence band close to S-MoO3's Fermi level, thus make it into a p-type semiconductor. S-MoO3 with smaller ionization energy and electron affinity is better suitable as an efficient AIL. On the basis of these AILs, a photovoltaic power conversion efficiency up to 3.69% has been achieved, which is 12% higher than that in pure MoO3 AIL case. The result thus shows that sulfur doping is a useful method to modify anode interface layer for improving the hole-transport properties of MoO3, which can improve the device performances.