Long-term stability remains a key issue impeding the commercialization of halide perovskite solar cells (HPVKSCs). The diffusion of molecules and ions causes irreversible degradation to photovoltaic device performance. Here, we demonstrate a facile strategy for producing highly stable HPVKSCs by using a thin but compact semimetal Bismuth interlayer. The Bismuth film acts as a robust permeation barrier that both insulates the perovskite from intrusion by undesirable external moisture and protects the metal electrode from iodine corrosion. The Bismuth-interlayer-based devices exhibit greatly improved stability when subjected to humidity, thermal and light stresses. The unencapsulated device retains 88% of its initial efficiency in ambient air in the dark for over 6000 h; the devices maintain 95% and 97% of their initial efficiencies after 85 °C thermal aging and light soaking in nitrogen atmosphere for 500 h, respectively. These sound stability parameters are among the best for planar structured HPVKSCs reported to date.

Perovskite solar cells have emerged as one of the most promising thin-film photovoltaic (PV) technologies and have made a strong debut in the PV field. However, they still face difficulties with up-scaling to module-level devices and long-term stability issue. Here, we report the use of a room-temperature nonvolatile Lewis base additive, diphenyl sulfoxide(DPSO), in formamidinium-cesium (FACs) perovskite precursor solution to enhance the nucleation barrier and stabilize the wet precursor film for the scalable fabrication of uniform, large-area FACs perovskite films. With a parallel-interconnected module design, the resultant solar module realized a certified quasi-stabilized efficiency of 16.63% with an active area of 20.77 cm². The encapsulated modules maintained 97 and 95% of their initial efficiencies after 10,000 and 1187 hours under day/night cycling and 1-sun equivalent white-light light-emitting diode array illumination with maximum power point tracking at 50°C, respectively.

Bathocuproine (BCP) buffer layer has been commonly used in inverted p–i–n perovskite solar cells (PSCs) for high performance, but its working mechanism has not been thoroughly elucidated. Here, a series of devices have been fabricated with controlled thicknesses of BCP layers deposited by thermal evaporation. With the aid of J–V data fitting by a single-diode model, the effect of BCP layer thickness on the device performance has been identified. An optimal power conversion efficiency (PCE) up to 17.9% has been obtained for the device with a critical BCP thickness of 5 nm, thanks to the formation of ohmic contact and reduction of interfacial charge recombination. While if the BCP layer is too thin or too thick, charge accumulation will emerge due to different mechanisms and lead to device performance degradation, which have been clearly confirmed by capacitance–voltage (C–V) characteristic displaying a peak capacitance at a certain bias region under illumination. The insertion of such a critical thin BCP layer between PCBM and Ag also resulted in long-term stability improvement of the devices, of which the T₈₀ lifetime increased from ∼6 hours to ∼50 hours in ambient air. This work gives insight into improving PSCs' performance through buffer layer's optimization, and the measurement of C–V characteristic provides a new clue to detect the defection of photovoltaic device associated with charge accumulation.

A one-step dual-additive strategy enables high-quality wide-bandgap perovskite films with efficient defect passivation, resulting in a certified record PCE of 44.72%, with a high V_oc of 1.069 V, and an FF of 82.3% under U30 light.