Tuning the Work Function of the Metal Back Contact toward Efficient Cu2ZnSnSe4 Solar Cells

Carrier collection is crucial for thin film photoelectronic devices. As photoelectronic devices, the undesirable energy band structure between the metal contact and p-type absorber is a serious limitation to boost the open-circuit voltage (V-OC) of thin film solar cells. Herein, the carrier collection near the back contact of a kesterite solar cell is promoted by tailoring the work function of the back contact. By diffusing P into Mo back contact of the kesterite solar cell, the work function of the Mo back contact is increased from 4.68 to 5.62 eV and the diffused P bonds with Mo as anions, thus resulting in the energy band bending upward at the back interface and enabling the fluent transmission of holes. The efficiency of Cu2ZnSnSe4 solar cells increases from 6.8% to 11.28%. The results expand the path to improving carrier collection in solar cells and electronic devices utilizing metal film contacts.