Impact of the Hafnium Oxide as Hole Blocking Layer on the Performance of Organic Solar Cells

Abstract

The effects of hafnium oxide (HfO2) as hole blocking layer (HBL) on the stability and degradation under air environment of inverted bulk heterojunction organic solar cells (iOSC), using as donor material thieno[3,4b]thiophene-alt-benzodithiophene (PTB7) and as acceptor material [6], [6]-phenyl C71 butyric acid methyl ester (PC 70 BM) are presented. The ultrathin films of HfO 2 layers 0.9 nm of thick were deposited by thermal evaporation. The highest power conversion efficiency obtained (PCE) was of 8.33%. The current density-voltage characteristic (J-V) was modeled through the ideal-diode equivalent circuit model. For comparison, cells with poly [(9,9-bis (30- (N,N-dimethylamino) propyl) −2,7-fluorene) -alt-2,7- (9,9-dioctylfluorene)] (PFN) and Zinc Oxide (ZnO) as hole blocking layer were fabricated. The three groups of cells were exposed to air for 1000 h. The electrical parameters extracted from the current density-voltage characteristic (J-V) were analyzed. The PCE for cells manufactured with HfO 2 as HBL remains around 30% after 1000 h under air environment, showing less degradation than iOSCs with ZnO.