Pulsed rapid thermal process for tailoring the surface sulfurization of CIGSe thin film at low temperature

Surface sulfurization is an effective way for CIGSe thin film to implement front graded bandgap. The controllable high S content with shallow diffusion depth into the film is key for the sulfurization. However, the degree of the sulfurization is closely related to the reaction temperature, thus it is difficult to control the diffusion depth of S into the CIGSe thin film effectively with high S content in such shallow depth. In this study, a pulsed sulfurization process is employed to realize a surface sulfurization as well as a high S content in a shallow diffusion depth of S into CIGSe at low substrate temperature, which provides an important way to fabricate double graded bandgap films prepared by post-selenization process. Structural analysis confirms the feasibility of the pulsed rapid thermal processing sulfurization. The device with surface sulfurization has the EA of N1 defects shifted to shallow position from 54 meV to 143 meV down to about 26 meV and 110 meV, respectively. The Voc, FF, and Jsc are improved obviously. Finally, the efficiency of CIGSSe thin film solar cell, based on the electrodeposition and selenization, increases by 20% with the improvement of Voc and FF. •A pulsed process is employed to realize a surface sulfurization at low temperature.•The feasibility of the pulsed rapid thermal processing was confirmed.•A double graded bandgap films were prepared.•The EA of N1 defects shifted to shallow position.•The efficiency of CIGSSe thin film solar cell increases by 20 % with the improvement of Voc and FF.