From planar-heterojunction to n-i structure: an efficient strategy to improve short-circuit current and power conversion efficiency of aqueous-solution-processed hybrid solar cells

In this paper, inverted hybrid solar cells (HSCs) with planar heterojunction (PHJ) and n-i structure are fabricated from an aqueous-solution-processed poly(p-phenylenevinylene) (PPV) precursor and 2-mercaptoethylamine (MA)-stabilized CdTe nanocrystals (NCs). Firstly, one densely stacked, smooth CdTe film with a wide absorption range and sufficient water resistance is obtained and used for fabricating the PHJ device. A PCE of 3.75% is obtained, which is comparable to the bulk-heterojunction (BHJ) devices. Secondly, the n-i structure is constructed by replacing the PPV layer with a mixed solution consisting of the PPV precursor and CdTe NCs. The n-i structure shows improved photocurrent with lowered fill factor (FF). The low FF is attributed to the severe phase separation of the PPV: CdTe layer, which is caused by the hydrophobicity of the annealed CdTe layer. Subsequently, the hydrophilicity of the annealed CdTe layer is improved by spin-coating an aqueous solution of CdCl2, which greatly increases the FF. Eventually, a record power conversion efficiency of 4.76% is achieved and the maximum J(sc) can reach 16.08 mA cm(-2).