Graphene Intermediate Layer in Tandem Organic Photovoltaic Cells

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 (Voc) of 1 V and a high short-circuit current density (Jsc) of 11.6 mA cm-2 could be obtained in series and parallel connection, respectively, in contrast to a Voc of 0.58 V and Jsc of 7.6 mA cm-2 in single PV cell. The value of Voc (Jsc) in the tandem cell is very close to the sum of Voc (Jsc) 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.