A Dual Layer of NiOx Hole-Transporting Material Boosting the Efficiency of Inverted Perovskite Solar Cells up to 20.7%

For the hole transport material (HTM) of methylammonium lead(II) triiodide (MAPbI 3 )-inverted perovskite solar cells (PVSCs), we have demonstrated that a dual layer of NiO x, a nanoporous NiO x (np-NiO x ) on a compact NiO x (cp-NiO x ), outperforms a single layer of cp-NiO x . With a dual layer of cp/np-NiO x HTM, we have achieved a PCE as high as 20.7%, which is one of the highest PCEs among inverted PVSCs using NiO x as HTM without doping NiO x or an interlayer between NiO x and the perovskite. In this report, scanning electron microscopy (SEM), atomic force microscopy (AFM), and photoluminescence (PL) spectroscopy have demonstrated that the interfacial contact of MAPbI 3 is better with np-NiO x than with cp-NiO x . Direct current conductivity measurements showed a higher conductivity of cp/np-NiO x compared to cp-NiO x . A deeper HOMO energy level was found for cp/np-NiO x compared to cp-NiO x . The space-charge limited current (SCLC) method estimated a higher trap-state density in cp-NiO x than in cp/np-NiO x . The studies of light intensity-dependent open-circuit voltage ( V OC ) and short-circuit current density ( J SC ) revealed a less charge recombination in cp/np-NiO x than in cp-NiO x PVSCs. We have also found and verified that using a larger volume of the ethylenediamine stabilizer in the preparation of np-NiO x results in a higher-performance cp/np-NiO x HTM.