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 Jsc can reach 16.08 mA cm−2.