The　effects　of　surface　modification　of　ZnO　ETL　by　H-plasma　treatment　on　the　performance　of　bulk　heterojunction　(BHJ)　solar　cells　were　systemically　investigated.　The　open　circuit　voltage　(VOC)　of　devices　was　dramatically　improved　after　Hplasma　treatment.　Both　Kelvin　probe　force　microscopy　(KPFM)　and　ultraviolet　photoelectron　spectroscopy　(UPS)　measurements　indicate　that　the　improved　VOC　is　attributed　to　the　reduced　work　function　of　ZnO　caused　by　H-plasma　treatment.　After　2.5　min　Hplasma　treatment,　the　power　conversion　efficiency　(PCE)　of　solar　cells　has　been　increased　from　3.03%　to　3.84%　with　a　high　VOC　of　0.670　V.　©　2018　IEEE.