Effect of strong base addition to hole-collecting buffer layer in polymer solar cells

We report a brief study on the effect of strong base addition to the hole-collecting buffer layer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)] on the performance of polymer solar cells made using blend films of poly(3-hexylthiophene) and soluble fullerene. A concentrated aqueous solution of sodium hydroxide (NaOH) was added to the PEDOT:PSS solution to decrease its acidity. The optical absorption spectra of modified buffer layers were measured to investigate the influence of NaOH addition on the spectral shape, while the surface of modified buffer layers was examined using atomic force microscopy. Results showed that the acidity of PEDOT:PSS solutions was remarkably reduced by adding the NaOH solution. However, the performance of solar cells was slightly degraded, which has been attributed to the decreased charge transportability as evidenced from the dark current-voltage characteristics.