An n -doped organic layer assists the anode modification of inverted organic solar cell for the efficiency improvement

Inverted organic solar cells have been fabricated with an anode modifying bilayer, comprised of thermally evaporated MoO 3 and ytterbium n -doped bathocuproine (BCP:Yb). In the bilayer, MoO 3 and BCP:Yb play the roles of forming ohmic contacts with photoactive layer and anode, respectively; due to the Fermi level alignment, MoO 3 and BCP:Yb form a low-barrier interface, benefiting hole injection and extraction. The MoO 3 /BCP:Yb bilayer enables higher open-circuit voltage of inverted device than the conventional MoO 3 layer, mostly because BCP:Yb suppresses the reduction of MoO 3 work function by anode. Moreover, the introduction of BCP:Yb helps increase the optical absorption of inverted device and thereby short-circuit current density. Although BCP:Yb gives increased electron mobility than MoO 3 , the MoO 3 /BCP:Yb bilayer decreases hole mobility of inverted device and thereby fill factor than the MoO 3 layer, mostly due to the interfacial p -doping effect of MoO 3 on BCP:Yb. The power conversion efficiency based on MoO 3 /BCP:Yb bilayer is 6.60%, higher than that (6.25%) based on the MoO 3 layer. The current research indicates that n -doped organic layers are helpful to improve the efficiencies of inverted OSCs via assisting the anode modification.