Enhanced efficiency of inverted polymer solar cells using surface modified Cs-doped ZnO as electron transporting layer

•Surface modified Cs-doped ZnO as ETL for inverted polymer solar cell.•Cs doping improves the conductivity of ZnO film.•Surface modification reduces the contact barrier between active layer and ETL.•PCE of the optimized device is improved from 2.98% to 4.03%.

Cs doping technique and surface modification by polar solvent ethanolamine (EA) has been introduced during the fabrication of ZnO electron transporting layer (ETL) for inverted polymer solar cell (iPSC) to improve its performance. The conductivity of 0.005 M Cs-doped ZnO (CZO) film exhibited one order of magnitude higher than that of undoped ZnO film, and Cs-doped ZnO film showed a rougher surface morphology resulting in a larger contact area between ETL and active layer. And the CZO films were modified by EA solution with different concentration to reduce the contact resistance and bimolecular recombination at the interface of ETL and active layer. The power conversion efficiency of the iPSC with CZO ETL modified by 1% EA was improved from 2.98% to 4.03% compared with that of the device with undoped ZnO ETL.