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.

To improve the gas-sensing performance of metal-oxide-semiconductors, the effect of defects on gas-sensing properties has been widely investigated. Nevertheless, although the metal cation defect is the dominative acceptor defect in p-type semiconductors, its effect on the gas-sensing properties remains blank, which leads to a hindrance for further developing p-type semiconductor-based gas sensors. Accordingly, to eleborate the effect of metal cation defects on the sensing properties, mesoporous NiO nanosheets with different amounts of nickel vacancies were prepared by annealing at different temperatures. It was found that the amount of nickel vacancies increased with increasing the annealing temperature. Gas-sensing studies revealed that the NiO with a higher concentration of nickel vacancies exhibited higher sensitivity to NO2 at room temperature. With further increasing the annealing temperature to 600 °C, although the rapid decrease in the specific surface area of the NiO might limit the physisorption of NO2, the NiO could also present a better sensitivity to NO2 due to the abundant nickel vacancies with high activity. Furthermore, an in situ DRIFTS study demonstrated that the number of adsorbed nitrate and nitrite species on NiO surfaces increased with increasing the amount of nickel vacancies, indicating that the nickel vacancies acted as the dominative active sites participating in the gas–solid reaction and then determined the room-temperature sensing properties. According to the defect ionization equation, a hole conduction model was further proposed to decipher the dependency of sensing properties on the metal cation defects. We hope this work could make us better understand the roles of cation defect in the sensing properties, and it could also benefit the improvement of p-type semiconductor-based gas sensors.