Stable aqueous amino-grafted silicon nanoparticles （SiNPs-NH2） were prepared via one-pot solution method. By grafting amino groups on the particle surface, the dispersion of SiNPs in water became very stable and clear aqueous solutions could be obtained. By incorporating SiNPs-NH2 into the hole transport layer of poly（3,4- ethylenedioxythiophene）/polystyrene sulfonic acid （PEDOT＇PSS）, the performance of polymer solar cells composed of poly[2-methoxy,5-（2＇-ethylhexyloxy）-1,4-phenylene vinylene] （MEH-PPV）：[6,6]-phenyl-C61-butyric acid methyl ester （PCBM） as active layer can be improved. SiNPs-NH2 are dispersed uniformly in the PEDOT：PSS solution and help form morphologies with small-sized domains in the PEDOT：PSS film. SiNPs-NH2 serve as screens between conducting polymer PEDOT and ionomer PSS to improve the phase separation and charge transport of the hole transport layer. As a result, the sheet resistance of PEDOT：PSS thin films is decreased from （93 ±5） × 10^5 to （13 ± 3） × 10^5 Ω/□. The power conversion efficiency （PCE） of polymer solar cells was thus improved by 9.8% for devices fabricated with PEDOT＇PSS containing 1 wt% of SiNPs-NH2, compared with the devices fabricated by original PEDOT：PSS.
