Lead sulfide quantum dots (PbS QDs) are an attractive material system for the development of low-cost photovoltaics (PV) due to their ease of processing and stability in air, with certified power conversion efficiencies exceeding 11%. However, even the best PbS QD PV devices are limited by diffusive transport, as the optical absorption length exceeds the minority carrier diffusion length. Understanding minority carrier transport in these devices will therefore be critical for future efficiency improvement. We utilize cross-sectional electron beam-induced current (EBIC) microscopy and develop methodology to quantify minority carrier diffusion length in PbS QD PV devices. We show that holes are the minority carriers in tetrabutylammonium iodide (TBAI)-treated PbS QD films due to the formation of a p–n junction with an ethanedithiol (EDT)-treated QD layer, whereas a heterojunction with n-type ZnO forms a weaker n⁺–n junction. This indicates that modifying the standard device architecture to include a p-type window layer would further boost the performance of PbS QD PV devices. Furthermore, quantitative EBIC measurements yield a lower bound of 110 nm for the hole diffusion length in TBAI-treated PbS QD films, which informs design rules for planar and ordered bulk heterojunction PV devices. Finally, the low-energy EBIC approach developed in our work is generally applicable to other emerging thin-film PV absorber materials with nanoscale diffusion lengths.

中文翻译：

---

硫化铅量子点光伏中的少数载流子传输

硫化铅量子点（PbS QDs）是低成本光伏（PV）开发的诱人材料系统，因为它们易于加工且在空气中稳定，认证的功率转换效率超过11％。但是，即使最好的PbS QD PV器件也受到扩散传输的限制，因为光吸收长度超过了少数载流子扩散长度。因此，了解这些设备中的少数载流子运输对于将来提高效率至关重要。我们利用截面电子束感应电流（EBIC）显微镜，并开发了方法来量化PbS QD PV器件中的少数载流子扩散长度。⁺ –n结。这表明修改标准设备体系结构以包括p型窗口层将进一步提高PbS QD PV设备的性能。此外，在TBAI处理的PbS QD膜中，定量EBIC测量得出的空穴扩散长度的下限为110 nm，这为平面和有序体异质结PV器件的设计规则提供了依据。最后，我们工作中开发的低能量EBIC方法通常适用于其他具有纳米级扩散长度的新兴薄膜PV吸收材料。