摘要： Although organic solar cells have surpassed the 17% power conversion efficiency threshold, commercial modules efficiencies are only around 4-5%. One of the reason, is the lack of effective solution processable hole transport materials, that are a key element for the scale up on roll-to-roll printing equipments and the commercial development. In this work, we have developed a class of novel vanadium and molybdenum polyoxometallate salts that, alone or in combination with a traditional poly(ethylene-3,4-dioxytiophene):poly(styrene sulfonate) (PEDOT:PSS) layer, can be employed as anodic buffer layer in inverted polymer solar cells. These materials exhibit work function values around 5.8 eV that match well with HOMO energies of typical polymer donors. They have been tested with different widely used active systems, including PTB7:PC71BM, PV2000:PCBM and PffBT4T:PC71BM. Vanadium and molybdenum polyoxometallate can be deposited from solutions and, contrary to PEDOT:PSS used alone, do not cause a drop of performances compared to evaporated molybdenum oxide (e-MoOx); on the contrary, in the best cases they achieve similar performances to e-MoOx. Slot-die coated PV2000:PCBM solar cells on flexible substrate achieve a remarkable power conversion efficiency of almost 7.6%.