Ag Incorporation with Controlled Grain Growth Enables 12.5% Efficient Kesterite Solar Cell with Open Circuit Voltage Reached 64.2% Shockley–Queisser Limit

The large open-circuit voltage deficit ( V oc,def ) is the key issue that limits kesterite (Cu 2 ZnSn(S,Se) 4 , [CZTSSe]) solar cell performance. Substitution of Cu + by larger ionic Ag + ((Ag,Cu) 2 ZnSn(S,Se) 4 , [ACZTSSe]) is one strategy to reduce Cu–Zn disorder and improve kesterite V oc . However, the so far reported ACZTSSe solar cell has not demonstrated lower V oc,def than the world record device, indicating that some intrinsic defect properties cannot be mitigated using current approaches. Here, incorporation of Ag into kesterite through a dimethyl sulfoxide (DMSO) solution that can facilitate direct phase transformation grain growth and produce a uniform and less defective kesterite absorber is reported. The same coordination chemistry of Ag + and Cu + in the DMSO solution results in the same reaction path of ACZTSSe to CZTSSe, resulting in significant suppression of Cu Zn defects, its defect cluster [2Cu Zn + Sn Zn ], and deep level defect Cu Sn . A champion device with an efficiency of 12.5% (active area efficiency 13.5% without antireflection coating) and a record low V oc,def (64.2% Shockley–Queisser limit) is achieved from ACZTSSe with 5% Ag content.