Water soluble amino grafted silicon nanoparticles and their use in polymer solar cells

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) × 10⁵ to (13 ± 3) × 10⁵ 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.