Light management in perovskite solar cell by incorporation of carbon quantum dots

In the conventional sandwich structure of perovskite solar cells (PSCs) with the metallic electrodes, the parasitic absorption losses due to the presence of glass substrate, conductive metal oxides and other functional layers below the perovskite film reduce a certain portion of photons that can be harvested by the perovskite absorber. The carbon quantum dots (CQDs) with down-converting properties can absorb high-energy UV light and convert them into the photons with lower energy lying in the visible light region. The CQDs can be used to enhance the light harvesting power of the PSCs so that the negative effect due to the parasitic absorption can be suppressed. In this work, a coating layer composed of CQDs is deposited on the illuminated side of the glass substrate. In contrast to our previous report, the deionized water (DIW) is used to disperse the CQDs instead of dispersing CQDs in the matrix of PMMA and chlorobenzene (CB). By using the new approach, the preparation of CQD coatings is more efficient and the use of toxic CB can be avoided. After systematic optimization of the preparation parameters, it is found that using water as the dispersion medium for CQDs can also yield the effective coatings for PSCs to enhance their light absorption power.