Disentangling degradation pathways of Narrow bandgap lead-tin perovskite material and photovoltaic devices

Narrow bandgap mixed lead-tin perovskites are critical for efficient all-perovskite multi-junction solar cells, but their poor stability under operating conditions is a significant challenge. This work investigates the instability causes under heat and light stress (ISOS L-2 conditions), showing phase, absorbance, and background hole density remain stable while device degradation occurs. The study identifies mobile ions as the primary source of early-time performance degradation and demonstrates that choosing alternative hole transport layers significantly mitigates this issue. Over time, impurity phase growth and hole transport material changes also impact performance, providing insights into the dominant degradation pathways for various device architectures.