Chenchao Xie

Nickel oxide (NiO _x ) is a common hole transport layer (HTL) in perovskite photovoltaics, but the chemical reactivity of NiOx surfaces accelerates degradation when contacting perovskites. We developed an ultrathin, conformal tin oxide (SnO _x ) interlayer to suppress interfacial reactivity between NiO _x and perovskite. SnO _x is typically an electron transport layer, but we show that the energy alignment can be modified for hole extraction using molecules with dipoles. This synergy yielded high efficiency in perovskite photovoltaic devices and showed an ~10x improvement in T 90 lifetime in open-circuit conditions under AM1.5G at 65°C. This structure also improves resilience to thermomechanical durability, as minimodules retained 95.7% of their initial performance after 1000 thermal cycles (−65° to 85°C), highlighting the importance of interfaces for robust perovskite photovoltaic modules.

Current encapsulation architectures for thin‐film metal halide perovskite do not adequately eliminate all ambient stressors. Here, we develop low transmission rate barrier layers using atomic layer deposited (ALD) aluminum oxide grown directly on the completed photovoltaic (PV) device stack to provide an additional seal, prior to full packaging. We investigate the effect of deposition temperature and oxidant chemistries on the barrier growth for protection of perovskite photovoltaic devices. We characterize the layers individually, then integrate into devices to detail the tradeoff between protection and deposition compatibility. To enhance compatibility and impermeability, we present an approach using water as the aluminum oxidant during nucleation and switching from water to ozone for the remainder of the growth. At 50 nm, the barrier results in a water vapor transmission rate (WVTR) of 4.5·10 ⁻⁴ g/m ² /day, and 1,000‐hour device stability under 45°C with 85% relative humidity without further packaging. This barrier provides sufficient protection to enable minimal degradation of the perovskite solar cells while completely submerged in water for 140 minutes. Additionally, we characterize the oxygen transmission rate (OTR) to be 0.49 cm ³ /m ² /day at 23°C and 0% relative humidity, which is 1.5 orders of magnitude improvement over the OTR of the current encapsulation.

A new electrochemical metric quantifies detrimental redox activity in nickel oxide hole transport layers, directly linking surface reactivity to solar cell efficiency and guiding targeted passivation for stable, high-performance photovoltaics.