Perovskite Solar Cells Employing a PbSO4(PbO)4 Quantum Dot-Doped Spiro-OMeTAD Hole Transport Layer with an Efficiency over 22%

2,2',7,7'-Tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9'-spirobifluorene (spiro-OMeTAD), the most widely used hole transport material in high-efficiency perovskite solar cells (PSCs), still has serious defects, such as moisture absorption and poor long-term conductivity, which seriously restrict further improvement of the power conversion efficiency (PCE) and stability of the cell. Herein, to overcome these problems, inorganic salt PbSO4(PbO)(4) quantum dots (QDs) are incorporated into spiro-OMeTAD as the hole transport layer (HTL) for the first time. The incorporated PbSO4(PbO)(4) QDs significantly hinder the agglomeration of lithium bis(trifluoromethanesulfonyl)-imide and improve the long-term conductivity through the oxidative interaction between PbSO4(PbO)(4) QDs and spiro-OMeTAD and hydrophobicity of the HTL. Furthermore, the spiro-OMeTAD:PbSO4(PbO)(4) composite film can effectively passivate perovskite defects at the perovskite/HTL interface, resulting in suppressed interfacial recombination. As a result, the PSC based on the spiro-OMeTAD:PbSO4(PbO)(4) HTL shows an improved PCE of 22.66%, which is much higher than that (18.89%) of the control device. PbSO4(PbO)(4) also significantly improves the moisture stability for 50 days at room temperature (at RH similar to 40-50%) without encapsulation. This work indicates that inorganic PbSO4(PbO)(4) QDs are crucial materials that can be employed as an additive in spiro-OMeTAD to enhance the efficiency and stability of PSCs.