Graphene Intermediate Layer in Tandem Organic Photovoltaic Cells

Abstract One strategy to harvest wide spectral solar energy is to stack different bandgap materials together in a tandem solar cell. Here, it is demonstrated that CVD grown graphene film can be employed as intermediate layer (IML) in tandem solar cells. Using MoO₃‐modified graphene IML, a high open circuit voltage (V_oc) of 1 V and a high short‐circuit current density (J_sc) of 11.6 mA cm^‐2 could be obtained in series and parallel connection, respectively, in contrast to a V_oc of 0.58 V and J_sc of 7.6 mA cm^‐2 in single PV cell. The value of V_oc (J_sc) in the tandem cell is very close to the sum of V_oc (J_sc) attained from two single subcells in series (parallel), which confirms good ohmic contact at the photoactive layer/MoO₃‐modified graphene interface. Work function engineering of the graphene IML with metal oxide is essential to ensure good charge collection from both subcells.