1：Experimental Design and Method Selection

Solvothermal route was selected to prepare CDs using DMF as the reaction medium while varying the source of carbon.

2：Sample Selection and Data Sources

Citric acid and gallic acid were used as carbon sources for synthesizing G-CDs and B-CDs, respectively.

3：List of Experimental Equipment and Materials

Fourier transform infra-red (FTIR) spectra and the X-ray photoelectron spectroscopy (XPS) data of the CDs were collected on a Nicolet Impact-410 IR spectrometer and PHI 5000 Versa Probe III (Physical Electronics) instrument respectively. The particle size distribution and zeta potential values were recorded on a Microtrac Nanotrac Wave particle size analyzer. The absorption and fluorescence emission spectra of the materials were recorded on a Shimadzu UV-2550 spectrophotometer and a Hitachi F-2700 fluorescence spectrophotometer respectively. A JEOL JEM 2100 instrument was used to record the transmission electron microscope (TEM) micrographs of the CDs.

4：Experimental Procedures and Operational Workflow

For preparing G-CDs, a solution of 0.6 g of citric acid in 20 mL DMF was prepared. Then 0.17 mL of ethylenediamine was added to it. The solution was then transferred to a Teflon lined autoclave and heated at 180 °C for 5 h. Once the solution cooled down, it was centrifuged and filtered with a 0.22 μm membrane. The solvent was then evaporated to obtain G-CDs in powder form. For synthesizing B-CDs, citric acid was replaced with gallic acid and 0.17 mL ethylenediamine was used to carry out the reaction.

5：Data Analysis Methods

The current density-voltage (J-V) characteristics of the DSSCs under irradiation of 1 Sun illumination (100 mW cm?2) were recorded on a Keithley 2400-LV Source Meter. The fill factors (FF) and photoconversion efficiencies (η) of the devices were calculated from the J-V plots.