Two quasi-interfacial p-n junctions observed by a dual-irradiation system in perovskite solar cells

In general,perovskite solar cells(PSC)with a sensitized or thin-film architecture absorb light from a single-side illumination,and carrier separation and transport only take place inside the active layer of the perovskite film.Herein,we demonstrated a dualirradiation PSC system in which light passes through both the fluorinated tin oxide(FTO)side and the Au electrode side,resulting in much faster interfacial charge carrier extraction and transportation than that in a single-irradiation system,in which light passes through from either the FTO or semitransparent Au electrode side.This dual-irradiation PSC system with a configuration of FTO/Cl-TiO_(2)/Mp-TiO_(2)/mixed perovskite/spiro-OMeTAD/Au/ITO can form two quasi-interfacial p-n junctions,which occur separately at the interfaces of TiO_(2)/perovskite and perovskite/spiro-OMeTAD.When the PSC device was illuminated simultaneously from both the FTO and Au/ITO sides,the PSC achieved a total power conversion efficiency(PCE)as high as 20.1%under high light intensity(1.4 sun),which is higher than PCE(18.4%)of a single-irradiation system.The time of flight(TOF)photoconductivity,small perturbation transient photovoltaic(TPV),finite-difference time-domain(FDTD)optical simulations,and dual illumination-sidedependent impedance spectroscopy(ISD-IS)were used to authenticate the presence of two quasi-interfacial p-n junctions in the PSC,creating more charge carriers than only one quasi p-n junction,and thus leading to a fast recombination process.