Li-Doped Front Interface Engineering Enables Flexible Kesterite Solar Cell With 12.31% Efficiency and Module With 7.85% Efficiency

Performance of flexible kesterite Cu 2 ZnSn(S, Se) 4 (CZTSSe) solar cell is mainly limited by large open-circuit voltage deficit ( V oc, def ) due to severe carrier recombination primarily caused by numerous defects at CZTSSe/CdS interface. Here, a modification strategy by doping Li ions at front interface is proposed to reducing carrier recombination, where the sample uniformly doped Li ions into CZTSSe absorber is the reference group. In this process, the secondary phases and defects in the CZTSSe absorber are effectively inhibited. Furthermore, the highly dense absorber enables a high-quality CZTSSe/CdS heterojunction, resulting in the decreased interface defect states from 2.90 × 10 15 to 9.00 × 10 14 cm −3 . These effects result in a reduced carrier recombination and decreased V oc, def . The flexible CZTSSe solar cell has achieved a power conversion efficiency of 12.31% with a V oc of 0.555 V. Additionally, the flexible devices with 1.22 cm 2 area (champion efficiency of 9.61%) are assembled into the flexible solar module (4.56 cm 2 area) with 7.85% efficiency and V oc of over 2 V by the shingled technology. The work provides insights for promoting the efficiency of flexible kesterite solar cells and demonstrates the viability of shingled technology for flexible solar modules.