Synergistic engineering of hole transport materials in perovskite solar cells

In this work, methylammonium lead triiodide (CH₃NH₃PbI₃) perovskite solar cells with efficiencies higher than 18% were achieved using a new nanocomposite hole transport layer (HTL) by doping poly(ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) with a mixed dopant of polyaniline (PANI) and graphene oxide (GO). A synergistic engineering between GO, PANI, and PEDOT:PSS was accomplished to introduce additional energy levels between perovskite and PEDOT:PSS and increase the conductivity of PEDOT:PSS. Kelvin probe force microscope results confirmed that adding GO to PEDOT:PSS/PANI composite significantly reduced the average surface potential. This increased the open circuit voltage (V_oc) to 1.05 V for the GO/PEDOT:PSS/PANI nanocomposite perovskite solar cells from the pristine PEDOT:PSS (V_oc = 0.95 V) and PEDOT:PSS/PANI (V_oc = 0.99 V). In addition, adding PANI to the HTLs substantially enhanced short circuit current density (J_sc). This was supported by the current sensing-atomic force microscopy (CS-AFM) and conductivity measurements. The PANI doped films showed superior electrical conductivity compared with those without PANI as indicated by CS-AFM results. PANI can fill the gaps between the microflakes of GO and give rise to more compact hole transport material (HTM) layer. This led to a higher J_sc after doping with PANI, which was consistent with the incident photon-to-current efficiency and electrochemical impedance spectroscopy results. The results of X-ray diffraction (XRD) and AFM indicated the GO/PANI doped HTMs significantly improved the crystallinity, topography, and crystal size of the perovskite film grown on their surface. A higher efficiency of 18.12% for p-i-n perovskite solar cells has been obtained by adding the mixed dopant of GO, PANI, and PEDOT:PSS, demonstrating better stability than the pristine PEDOT:PSS cell. (Figure presented.).