Effect of a Co-evaporated Alq3:Liq cathode buffer layer on the performance of a polymer photovoltaic cell

Abstract

The effect of co-evaporated tris(8-hydroxyquinolinato)aluminium:8-hydroxy-quinolinato lithium (Alq3:Liq) on the performance of a photovoltaic (PV) cell was investigated by characterizing the performance of a PV cell fabricated on poly (3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl- C61butyric-acidmethyl-ester (PCBM) bulk heterojunctions with Alq3:Liq as an exciton/holeblocking and electron-injection layer. Inserting Alq3:Liq layer into the PV cell strongly affected the power conversion efficiency (PCE) and fill factor (FF) of the PV cell; i.e., 1-nm-thick Alq3:Liq layer increased the PCE and the FF of the PV cell by 55.22 and 7.15%, respectively, compared with the cell without the Alq3:Liq layer. In particular, the PCE and the short circuit current density (J SC ) of the PV cell with an Alq3:Liq layer were 4.14 and 6.2% higher than those of a 2,9-dimethyl- 4,7-diphenyl-1, 10-phenanthroline (BCP)/LiF bi-layer cell, respectively, because the Liq deposited on Alq3 reduced the electron injection barrier between the workfunction of the aluminum electrode and the lowest unoccupied molecular orbital (LUMO) level of the organic material, resulting in the peak of the binding energy moving toward the high highest occupied molecular orbital (HOMO) level.