Performance improvement of perovskite solar cells using vanadium oxide interface modification layer

To improve the performance of perovskite solar cells (PSCs), vanadium oxide (VO_x) film was deposited as an interface modification layer (IML) by a radio frequency magnetron sputtering system. The VO_x IML was utilized to modify the interface between the indium tin oxide (ITO) anode electrode and the poly(3,4-ethylenedioxythiophene)-poly (styrene sulfonate) (PEDOT:PSS) hole transport layer (HTL). The valence band maximum (VBM) of 4.94 eV of the VO_x films was measured by an ultraviolet photoelectron spectroscopy (UPS). Using the optical energy bandgap and the VBM of the VO_x film, the conduction band minimum (CBM) energy level was 2.12 eV. This phenomenon verified that the VO_x IML could be an electron blocking layer and made a more match energy level between the work function of ITO anode electrode and the highest occupied molecular orbital (HOMO) of PEDOT:PSS HTL. Using the measurement of contact angle, the surface energy of PEDOT:PSS HTL spun on VO_x IML and ITO anode electrode was evaluated as 47.76 mJ/m² and 38.21 mJ/m², respectively. The enhanced surface energy of the PEDOT:PSS HTL spun on VO_x IML could improve the adhesion ability of the perovskite absorption layer spun on the PEDOT:PSS HTL. Consequently, the carrier extraction could be enhanced and the leakage current could be reduced by the predominant functions of VO_x IML. Therefore, the performances of the PSCs were significantly improved. The power conversion efficiency (PCE) of the PSCs with VO_x IML was enhanced from 9.43% to 13.69% in comparison with the conventional PSCs without VO_x IML.