The alkanediol series such as 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol and 1,10-decanediol was introduced to poly(3-hexylthiophene, P3HT):[6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) based bulk-heterojunction (BHJ) polymer solar cells as processing additives. When 1,3-propanediol was introduced to photo-active layer as a processing additive, power conversion efficiency (PCE) was dramatically increased from 3.5% (for the reference device) to 5.3%. To investigate the causes of improvement of the PCE of PSCs after addition of alkanediol series, photon absorbance properties were observed using UV-vis spectroscopy and photoluminescence (PL). Then, the degree of crystallinity of P3HT was examined through X-ray analysis. In addition, changes in the nano-structure and surface morphology of P3HT:PCBM blend film were observed through AFM and TEM. The series resistance (R-S) of the fabricated PSCs was 5.19 Omega cm(2), and short circuit current density (J(SC)), open circuit voltage (V-OC) and fill factor (FF) were 16.2 mA/cm(2), 0.63 V and 51.9% respectively. (C) 2013 Elsevier B.V. All rights reserved.