Organic Solar Cells With Zn₂SnO₄ Nanoparticles As The Electron Extraction Layer

Bulk heterojunction?BHJ?organic photovoltaics?OPVs?have attracted tremendous effort due to its intrinsic merits of low-cost,flexibility and possibility of high throughput manufacturing.The power conversion efficiency of the solution-processed OPVs have exceeded 11%,further development is required to ensure a bright industrial future for OPVs.So far,tremendous efforts including developing novel narrow band-gap conjugated polymers that have broaden absorption spectra,high charge carrier mobility,and even unique edge-on molecular packing patterns and reengineering the interfaces via functional buffer layers,have been devoted to boost the power conversion efficiencies of OPVs.In this work,we introduced Zn₂SnO₄ nanoparticles?Zn₂SnO₄ NPs?as the electron extraction layer?EEL?to improve the performance of the inverted polymer solar cell?i-PSC?.Zn₂SnO₄ nanoparticles was synthesized through a facile hydrothermal route??100 ??,then the size of nanoparticles,the morphology and transmittance of Zn₂SnO₄ NPs film were systematically studied.In order to explore the effect of Zn₂SnO₄ NPs on the performance of i-PSC,ZnO was introduced for comparison.The i-PSC by poly[4,8-bis?2-ethylhexyloxyl?benzo[1,2-b:4,5-b?]dithio-phene-2,6-diylaltethylhexyl-3-flu-orothithieno[3,4-b]thiophene-2-ca rboxylate-4,6-diyl]?PTB7?blended with?6,6?-phenyl-C71-butyric acid methylester(PC₇₁BM)bulk heterojunction?BHJ?composite using the Zn₂SnO₄ NPs EEL exhibits comparable device performance with the i-PSC by PTB7:PC₇₁BM BHJ composite using the ZnO EEL.To further improve the performance of the i-PSC,poly[?9,9-bis?30-?N,Ndimethylamino?propyl?-2,7-fluorene?-alt-2,7-?9,9-dioctylfluorene?]?PFN?is used to modify the surface properties of Zn₂SnO₄ NPs thin film.By using the Zn₂SnO₄ NPs/PFN as the EEL,the i-PSC fabricated by PTB7 blended with PC₇₁ BM BHJ composite,exhibits a power conversion efficiency?PCE?of 8.44%,which is nearly 10% enhancement as compared with that of 7.75% observed from the i-PSC by PTB7:PC₇₁BM BHJ composite using the ZnO/PFN EEL.The open-circuit voltages,short-circuit current densities and fill factors of the i-PSCs using the ZnO/PFN or Zn₂SnO₄ NPs/PFN as the EEL were simultaneously improved,and consequently their power conversion efficiencies The enhanced PCEs are originated from improved interfacial contact between the EELs with BHJ active layer and good energy level alignment between BHJ active layer and the EELs.Considering the easily formed defects in Zn₂SnO₄ NPs thin film,the short-circuit current density of the i-PSC with Zn₂SnO₄ NPs /PFN EEL is dramatically enhanced after PFN modifying the defective Zn₂SnO₄ NPs surface,from 15.07 mA/cm² to 16.73 mA/cm².