In this work, the role of fullerene loading on the nanomorphology and photovoltaic performance of alternating copolymer poly{2-octyldodecyloxy-benzo[1,2-b;3,4-b]dithiophene-alt-5,6-bis(dodecyloxy)-4,7bis(thiophen-2-yl)-benzo[c][1,2,5]-thiadiazole}(PBDT-ABT-1) blend films were investigated. Morphology of blend films with different PCBM mixing ratios and solvent additive were studied using atomic force microscopy (AFM) and energy filtered transmission electron microscopy (EFTEM). From the AFM and EFTEM images it was observed that 1:1,1:2,1:3 weight ratio of PBDT-ABT-1:PCBM intermixed domain showed increased domain size with increasing PCBM weight ratio due to amorphous nature of polymer which tends to intermix with the polymer. X-ray diffraction measurements on the pristine polymer and blend films casted without additive showed amorphous nature of PBDT-ABT-1. EFTEM donor acceptor composite images showed intermixed domain and was conducted to see the bulk morphology i.e domain composition in the granular morphology . Furthermore, EFTEM composite image for additive cast film gave clear insight that addition of solvent additive di-iodooctane leads to more purer domain. Photo CELIV measurement indicated fast charge extraction in case of the optimized nanomorphology sample with the weight ratio of 1:2 corresponding to highest bimolecular recombination life time and mobility.