Chloride gradient render carrier extraction of hole transport layer for high V_oc and efficient inverted organometal halide perovskite solar cell

A carrier transport layer and its interfacial effects on an organometal halide perovskite light harvesting layer play an influential factor in either photovoltaic performance or long-term stability of a perovskite solar cell (OHPSC). Although the understandings of the carrier transport layers and interfacial effects on regular structured OHPSCs have been explored, knowledge of an interface between hole transport layer of NiO_x and perovskite in an inverted OHPSC is still necessary to be developed. Here, we performed a universal NiO_x film with the sequential passivation strategy of NiCl₂ (SPS-NiCl₂ treatment) for either wide bandgap or narrow bandgap of OHPSCs. The SPS-NiCl₂ treated NiO_x film not only implements the passivation at the perovskite layer/NiO_x film interface but also confers itself a gradient energy level of valance band inducing by chloride. Comprehensive characterizations reveal that the SPS-NiCl₂ treated NiO_x film suppresses non-radiative recombination at the interface and enlarges the splitting of the quasi-Fermi level at the interfaces. The photoconversion efficiency (PCE) of the champion device comprised of the SPS-NiCl₂ treated NiO_x film can achieve 19.53% with a record V_oc of 1.16 V, the lowest V_oc deficit of 390 mV in NiO_x based inverted OHPSCs. The corresponding devices with encapsulation also exhibit superior long-term stability, and over 80% of initial PCE can be maintained after 1500 h damp-heat test. This study sheds the light on managing the interfacial issues of an inverted OHPSC and offers a feasible path to develop a universal hole transport layer for perovskite layers with different energy bandgap.