Unveiling the damp-heat-induced degradation mechanism of AZO-incorporated silicon heterojunction solar cells and modules

Aluminum-doped zinc oxide (AZO) film is a promising alternative to indium tin oxide (ITO), typical transparent conductive oxide (TCO) used in silicon heterojunction (SHJ) solar cells. However, the long-term damp heat (DH) stability of AZO-based SHJ devices remains a critical concern due to the moisture sensitivity of AZO. In this work, the mechanism of damp-heat-induced degradation (DHID) of AZO-incorporated SHJ solar cells and modules was systematically investigated and compared with ITO references. After 1000 h of DH exposure at 85 °C and 85% relative humidity, AZO-incorporated SHJ solar cells exhibited a larger efficiency loss than the ITO reference, mainly associated with a significant reduction in fill factor (FF). The FF degradation was strongly correlated with an increase in series resistance (Rs), and the increase in AZO film resistivity was identified as an important contributor to the Rs increase observed during DH exposure. X-ray photoelectron spectroscopy (XPS) revealed a pronounced increase in the OH− intensity after DH testing, suggesting moisture-induced chemical modification of the AZO surface or near-surface region. Moreover, the observed open-circuit voltage (Voc) degradation after DH exposure implies that moisture-related degradation may extend beyond the AZO surface and affect underlying passivation layers. In addition, scanning electron microscopy (SEM) revealed the formation of surface grooves on the AZO film after DH exposure. These observations, together with the electrical degradation of the AZO films and devices, are consistent with moisture-induced degradation of AZO. Furthermore, a MgF2 capping layer improved the DH stability of AZO-incorporated SHJ solar cells by mitigating moisture-induced degradation.