Ultrathin Ammonium Heptamolybdate Films as Efficient Room-Temperature Hole Transport Layers for Organic Solar Cells

Ammonium heptamolybdate (NH4)(6)Mo7O24 center dot 4H(2)O (ARM) and its peroxo derivatives are analyzed as solution-processed room temperature hole transport layer (HTL) in organic solar cells. Such ARM based HTLs are investigated in devices with three different types of active layers, i.e., solution-processed poly(3-hexylthiophene)/[6,6]-phenyl C-61-butyric acid methyl ester(P3HT/PC60NM), poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]/[6,6]-phenyl C-70-butyric acid methyl ester(PCDTBT/PC70BM) and evaporated small molecule chloro-(subphthalocyaninato)boron(III) (SubPc)/C-60. By virtue of their high work functions, ARM based HTLs outperform the commonly used poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) HTL for devices employing deep HOMO level active materials. Moreover, devices using AHM based HTLs can achieve higher short circuit current (J(sc)) than the ones with evaporated molybdenum oxide(eMoO(3)), and thus better power conversion efficiency (PCE). In addition, P3HT/PC60BM devices with ARM based HTLs show air stability comparable to those with eMoO(3), and much better than the ones with PEDOT:PSS.