Fig. 1. (Color online) (a) The in-plane conductivity of HTL films with 0–2 mg/mL MoO_x or MoO₃ incorporated into PEDOT:PSS. (b) I–V curves test for Ag/MoO₃/ITO and Ag/MoO_x/ITO.

Fig. 2. (Color online) XPS profiles of (a) MoO₃ and (b) MoO_x.

Fig. 3. (Color online) (a) Device construction of the planar PSCs, and (b) cross-sectional SEM image of the planar PSC structures without an Ag electrode.

Fig. 4. (Color online) (a) The best J–V characteristics under illumination for the devices using pristine PEDOT:PSS, PEDOT:PSS-MoO_x, and PEDOT:PSS-MoO₃ as HTLs. (b) Histogram of PSCs using PEDOT:PSS-MoO_x and PEDOT:PSS-MoO₃ as HTLs.

Fig. 5. (Color online) Average photovoltaic parameter for 12 devices: (a) open-circuit voltage (V_oc), (b) series resistance (R_s), (c) short-circuit current density (J_sc), (d) fill factor (FF).

Fig. 6. (Color online) Nyquist plot of devices with various HTLs (pristine PEDOT:PSS, PEDOT:SS-MoO_x and PEDOT:PSS-MoO₃). Solid symbols are experimental results and solid lines are fitted results.

Fig. 7. (Color online) (a) OCVD measurements for three types of devices. (b) Schematic of the proposed mechanism for the trap-assisted recombination.

Fig. 8. (Color online) (a) Real part of the dielectric constant as a function of frequency in the dark. (b) Schematic diagram of electric-field distribution in the perovskite device based on PEDOT:PSS-MoO_x. (c) J–V plots of the perovskite devices based on PEDOT:PSS-MoO_x and PEDOT:PSS-MoO₃ at different scanning directions taken in the dark, inset: the schematic diagraph of testing.