An alternative hole extraction layer for inverted organic solar cells

MoO3 p-doped 4,4′-N,N′-dicarbazole-biphenyl (CBP:MoO3) has been used as a hole extraction layer in inverted organic solar cells (OSCs). It is found that although the CBP:MoO3 shows reduced conductivity than the conventional hole extraction layer of MoO3, the CBP:MoO3 yields nearly the same quasi-Fermi level for holes in a photoactive layer as the MoO3 does. As a result, the open-circuit voltages of inverted OSCs based on CBP:MoO3 and MoO3 remain almost unchanged. When the thickness of hole extraction layer is ≤ 20 nm, the CBP:MoO3 can enable nearly the same short-circuit current density of inverted device but improved fill factor, in comparison to the MoO3, leading to the power conversion efficiency based on CBP:MoO3 higher than that based on MoO3. The results show that the CBP:MoO3 can act as an useful hole extraction material for fabricating high-efficiency inverted OSCs.