An alternative hole extraction layer for inverted organic solar cells

MoO 3 p -doped 4,4′- N,N ′-dicarbazole-biphenyl (CBP:MoO 3 ) has been used as a hole extraction layer in inverted organic solar cells (OSCs). It is found that although the CBP:MoO 3 shows reduced conductivity than the conventional hole extraction layer of MoO 3 , the CBP:MoO 3 yields nearly the same quasi-Fermi level for holes in a photoactive layer as the MoO 3 does. As a result, the open-circuit voltages of inverted OSCs based on CBP:MoO 3 and MoO 3 remain almost unchanged. When the thickness of hole extraction layer is ≤ 20 nm, the CBP:MoO 3 can enable nearly the same short-circuit current density of inverted device but improved fill factor, in comparison to the MoO 3 , leading to the power conversion efficiency based on CBP:MoO 3 higher than that based on MoO 3 . The results show that the CBP:MoO 3 can act as an useful hole extraction material for fabricating high-efficiency inverted OSCs.