To overcome small/indirect-bandgap nature of Si, a lot of efforts have been made to employ nanostructured Si such as Si quantum dots (SQDs) or porous Si (PSi) in optoelectronic devices based on quantum confinement effect. We first report PSi heterojunction solar cells with 4.0 % power conversion efficiency (PCE) by employing graphene transparent conductive electrodes (TCEs) doped with Ag nanowires (Ag NWs). Co-doping of graphene with Au nanoparticles and bis(trifluoromethanesulfonyl)-amide enhances the PCE to 10.7 %. We also employ graphene TCEs doped with AuCl3 or Ag NWs for SQDs-based solar cells, showing 16.2% PCE, much larger than ever achieved in SQDs solar cells with metal TCEs as well as in bulk-Si solar cells with graphene TCEs. The encapsulation of the doped graphene TCEs with another graphene layer prevents the doping elements from being desorbed, thereby making the PCE higher, its doping dependence more evident, and the long-term performance more stable.