Journal Article perovskite solar cells solar cells 1 µm-thick photoactive layer CsPbI3 CsPbI3 quantum dots CsPbI3 quantum dots solar cells P/N homojunctions PbS quantum dots block copolymers charge transfer charge-transfer doping di-n-propylamine guanidinium thiocyanate hybrid heterointerfaces interfacial passivation large-scale printing technology lead sources ligand exchange perovskite quantum dots surface ligand engineering surface passivation