Enhanced performance of polymer solar cell with ZnO nanoparticle electron transporting layer passivated by in situ cross-linked three-dimensional polymer network

An in situ cross-linked three-dimensional polymer network has been developed to passivate ZnO nanoparticles as an electron transporting layer (ETL) to improve the performance of inverted organic solar cells. The passivated ZnO ETL-based devices achieve efficiencies of 3.26% for poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) and 7.37% for poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl]] (PTB7):[6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) devices compared with 2.58% and 6.67% for the control devices respectively. The origin of the improvement is studied by investigating the influence of the transport barrier, morphology and recombination. Atomic force microscopy (AFM), photoluminescence (PL) and transient photocurrent (TPC) measurements prove the boosted performance originates from the improved film-forming quality as well as passivated defects in the ZnO film, decreasing the trap-assisted recombination rather than giving better energy alignment between the active layer and the ZnO interlayer.