The thickness of the CdS:O window layer plays an important role in CdTe-based thin-film solar cell performance. Normally with thinner CdS:O layer, the cells’ short wavelength response can be enhanced to achieve higher short-circuit current density (J_sc), while the open-circuit voltage (V_oc) and fill factor (FF) would degrade. Previous research finds that reducing the CdS:O layer thickness to less than 40 nm would decrease the cells’ efficiency (Eff.). In this work, 18% efficiency CdTe thin-film solar cell with only 30 nm CdS:O window layer is demonstrated. A post annealing process is developed to fabricate high efficiency cells with ultrathin CdS:O layers. Our results indicate that the high defect density in CdTe absorber, low built-in potential (V_bi) and high back contact barrier (Φ_b) are partially responsible for the reduced V_oc and FF of cells with ultrathin CdS:O layers. The post annealing process can increase the carrier concentration (N_CV) and V_bi, and decrease the Φ_b, in which way improves V_oc and FF for higher cell efficiency.

CdS：O窗口层的厚度在基于CdTe的薄膜太阳能电池性能中起着重要作用。通常，使用更薄的CdS：O层，可以增强电池的短波长响应，以实现更高的短路电流密度（J _sc），而开路电压（V _oc）和填充因子（FF）则会降低。先前的研究发现，将CdS：O层的厚度减小到40 nm以下会降低电池的效率（Eff。）。在这项工作中，展示了只有30 nm CdS：O窗口层的18％效率的CdTe薄膜太阳能电池。开发了后退火工艺以制造具有超薄CdS：O层的高效电池。我们的研究结果表明，在CdTe吸收，低内建电势的高缺陷密度（V _BI）和高背接触阻挡（Φ _b）是用于缩小部分负责V _OC和FF与超薄的CdS细胞：O型层。后退火处理可以提高载流子浓度（Ñ _CV）和V _BI，并减小Φ _b，以何种方式提高V_oc和FF可提高电池效率。