Water‐Soluble V ₂ O _5‐x Enables Efficient Inverted Perovskite Solar Cells With High Operational and Reverse Bias Stability

ABSTRACT Perovskite solar cells (PSCs) face challenges in long‐term stability, especially under reverse bias. Here, a water‐soluble vanadium pentoxide (V 2 O 5‐x ) hole‐collecting layer (HCL) is introduced into inverted PSCs to improve the photovoltaic performance and multiple‐scenario stability under operational, thermal recycle, and reverse bias. V 2 O 5‐x annealed at 50–250°C are characterized for multiple physical properties, revealing that 150°C annealing optimizes oxygen vacancy to reduce trap density and improve interface carrier collection. The champion device based on (FA 0.83 MA 0.17 ) 0.95 Cs 0.05 Pb(I 0.95 Br 0.05 ) 3 absorber achieves power conversion efficiency (PCE) of 23.3% with negligible hysteresis (HI = 0.64%) and good stability (retains ∼88% of initial PCE after 1000 h of storage). Further, with Cs 0.05 MA 0.1 FA 0.85 PbI 3 as absorber, the PCE of the device can be further improved to be 25.88% with an HI of 3.26%, superior to the device without V 2 O 5‐x (PCE = 24.94%, HI = 5.47%). Moreover, the operational and thermal cycling stability of the device has been obviously improved. Crucially, V 2 O 5‐x enhances the reverse breakdown voltage from about |−2| to |−6| V, endowing the device with higher reverse bias stability and tolerance to the shadow effect. These results demonstrate that V 2 O 5‐x can simultaneously boost PCE and stability of PSCs, offering a promising route toward efficient and durable PSCs.