Fabrication and characterization of inverted organic PTB7:PC70BM solar cells using Hf-In-ZnO as electron transport layer

In this study, we report the use of Hafnium-Indium-Zinc-Oxide (HIZO) as electron transport layer (ETL) in inverted organic solar cells (iOSCs) using a bulk heterojunction of Poly({4,8-bis[(2-ethylhexy)oxy]benzo[1,2-b:4,5-b'] dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl)) (PTB7) and [6,6)-phenyl C71 butyric acid methyl ester (PC70BM) as active layer. The absorption spectrum and performance parameters obtained are compared to those obtained for similar iOSCs where the ETL was poly [(9,9-bis (30-(N,N-dimethylamino) propyl) -2,7-fluorene) -alt-2,7- (9,9-dioctylfluorene)] (PFN). Initially, devices showed the S-shaped current-voltage curve that has been modeled using a three-diode equivalent circuit model. This phenomenon can be removed by repeating electrical sweep-cycles under illumination. The degradation under nitrogen atmosphere and under encapsulation was also analyzed and compared with the degradation of the iOSCs using PFN. It was observed that the degradation of encapsulated HIZO-iOSC was twice slower than that of PFN-iOSCs. This increase in stability can be attributed to the Hf atoms, which have a stronger thermodynamic tendency to form metal oxides, suppressing the dissociation of HIZO.