Kesterite Cu2ZnSn(S,Se)4 solar cells fabricated from DMSO molecular solutions exhibit very different open circuit voltage (Voc) when tin precursor has different oxidation state (Sn2+ vs Sn4 ). Here, the grain...

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The large open‐circuit voltage deficit (Voc,def) is the key issue that limits kesterite (Cu2ZnSn(S,Se)4, [CZTSSe]) solar cell performance. Substitution of Cu+ by larger ionic Ag+ ((Ag,Cu)2ZnSn(S,Se)4, [ACZTSSe]) is one strategy to reduce Cu–Zn disorder and improve kesterite Voc. However, the so far reported ACZTSSe solar cell has not demonstrated lower Voc,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 CuZn defects, its defect cluster [2CuZn + SnZn], and deep level defect CuSn. A champion device with an efficiency of 12.5% (active area efficiency 13.5% without antireflection coating) and a record low Voc,def (64.2% Shockley–Queisser limit) is achieved from ACZTSSe with 5% Ag content.

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