1：Experimental Design and Method Selection

Cu2O and Cu2O:B films were deposited by rf-magnetron sputtering in oxygen and argon ambience. The optical and electrical properties of the doped and undoped films were investigated.

2：Sample Selection and Data Sources

Flat zone c-Si(n) wafer of (100) orientation was used for fabrication of the solar cells. The thickness of the deposited films was measured using Ellipsometry and stylus thickness profilometer.

3：List of Experimental Equipment and Materials

Cu and B targets of 99.99% purity were used for the deposition. Equipment included Ellipsometry (J A Woolam Alpha SE), stylus thickness profilometer (Dektak6M), Hall measurements (Ecopia HMS-3000), XRD (PANalytical X’Pert PRO system), Raman spectrometer (Horiba Jobin-Yvon LabRam HR), XPS and UPS (Kratos Analytical AMICUS spectrometer), UV–vis–NIR spectrophotometer (Jasco V-570), AFM (Keysight 5500), FESEM (Carl Zeiss Sigma), lifetime measurement (Sinton WCT 120), and semiconductor parameter analyser (Keithley 2400).

4：Experimental Procedures and Operational Workflow

The wafer was randomly textured at one side to improve the light absorption. After standard RCA1 and RCA2 processes, the wafer was dipped in 2% HF. A thin SiOx tunnel oxide was deposited to prevent Cu diffusion. ITO was deposited as the top electrode/anti-reflecting layer. The cell was completed by evaporating the metal contacts.

5：Data Analysis Methods

The band alignment of the Cu2O:B/Si heterojunction was analysed using UV-VIS-NIR spectroscopy along with UPS and XPS measurements. The valance band offset and conduction band offset were calculated.