Effect of a symmetry breaking layer on the open circuit voltage of conventional buIk-heterojunction solar cells

摘要

Solution processable titanium suboxide (TiO_x) was introduced as an artificial symmetry breaking layer in bulk-heterojunction (BHJ) solar cells comprising a low band gap conjugated polymer, poly[(4,4'-bis(2-ethylhexyl)dithiene[3,2-b:2',3'-d]silole)-2,6-diyl-alt-(4,7-bis(2-thienyl)-2,l,3-benzothiadiazole)-5,5'-diyl] (Si-PCPDTBT), and a soluble fullerene, [6,6]-phenyl-C_(71)-butyric methyl ester (PC_(71)BM). The inserted TiO_x layer obviously extracted the same level of open circuit voltage (V_(oc)) regardless of metal work function. Ultraviolet photoelectron spectroscopy (UPS) results indicated that the formation of the interface dipole between the TiO_x symmetry breaking layer and metal electrode successfully modifies the effective work function of the cathode electrode, thereby leading to symmetry breaking in BHJ solar cells.