Efficiency Limit of Colloidal Quantum Dot Solar Cells: Effect of Optical Interference on Active Layer Absorption

摘要： Recently, colloidal quantum dot (CQD) solar cells have drawn intense attention because of their accessibility in low-energy solar photons with a facile tunability in electrical properties and their promising feature to go beyond the classic Shockley?Queisser limit of solar cells. Currently, state-of-the-art performance lead sulfide CQD thin-film-based solar cells have a PCE of approximately 12% with large room for improvement. To overcome current limitations on efficiency enhancement in CQD thin-film solar cells, the active layer thickness must increase first by improving carrier transport and formation of band bending to improve collection of carriers. We must note, however, in this heterojunction architecture, estimated optimal active layer thickness has to be revisited considering the interference effect. Specifically, the large refractive index difference between the PbS CQD layer and the ZnO layers account for a significant Fresnel reflection and optical interference in PbS CQD solar cells. This interference effect on high-performing PbS CQD solar cells may not only reduce the effective light absorption but also lead to underestimating the optimal active layer thickness.