Fig. 4. (a) The space-charge-limited-current (SCLC) of hole-only devices with the configuration of indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene)–polystyrene sulfonate (PEDOT:PSS)/p,p-spiro-OMeTAD or IDIDF (with Li-bis(trifluoromethanesulfonyl)imide (Li-TFSI) and 4-tert-butylpyridine (tBP) as additives)/Au. (b) PL emission spectra of perovskite/PMMA, perovskite/p,p-spiro-OMeTAD, and perovskite/IDIDF film under excitation at 670 nm.