Aqueous solution-processed MoO3 as an effective interfacial layer in polymer/fullerene based organic solar cells

► Water-soluble MoO3 (sMoO3) was used to form a thin layer in organic solar cells. ► The preparation of sMoO3 layer is simple and environment-friendly. ► sMoO3 based devices are comparable to that of PEDOT:PSS in conversion efficiency. ► A better stability was obtained from sMoO3 based devices.