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Ag-and Sn-doped In 2 S 3 thin films were deposited on glass substrates using the thermal evaporation technique. The doping was realized by thermal diffusion. The influences of Ag and Sn impurities on the electrical, structural, morphological, and optical properties of the In 2 S 3 films were investigated. In all deposited samples, the x-ray diffraction spectra revealed the formation of cubic In 2 S 3 phase. A significant increase in the crystallite size was observed after Ag doping, while the doping of Sn slightly decreased the crystallite size. The x-ray photoelectron spectroscopy verified the diffusion of Ag and Sn into the In 2 S 3 films after annealing. The optical study illustrated that Ag doping resulted in a reduction of the optical band gap while Sn doping led to a widening of the gap. Optical properties were investigated to determine the optical constants. Besides, it was found that the resistivity decreases significantly either after Ag or Sn incorporation. The study demonstrates that the Sn-doped In 2 S 3 thin films are more suitable for buffer layer application in solar cells than the Ag-doped In 2 S 3 thin films.

The Cu2ZnSnS4 (CZTS)-based solar cell is numerically simulated by a one-dimensional solar cell simulation software analysis of microelectronic and photonic structures (AMPS-1D). The device structure used in the simulation is Al/ZnO:Al/nZn(O,S)/pCZTS/Mo. The primary motivation of this simulation work is to optimize the composition in the ZnO1−𝑥S𝑥 buffer layer, which would yield higher conversion efficiency. By varying S/(S+O) ratio 𝑥, the conduction band offset (CBO) at CZTS/Zn(O,S) interface can range from −0.23 eV to 1.06 eV if the full range of the ratio is considered. The optimal CBO of 0.23 eV can be achieved when the ZnO1−𝑥S𝑥 buffer has an S/(S+O) ratio of 0.6. The solar cell efficiency first increases with increasing sulfur content and then decreases abruptly for 𝑥 > 0.6, which reaches the highest value of 17.55% by our proposed optimal sulfur content 𝑥 = 0.6. Our results provide guidance in dealing with the ZnO1−𝑥S𝑥 buffer layer deposition for high efficiency CZTS solar cells.

Tantalum (Ta)-doped titanium oxide (TiO2) thin films are grown by plasma enhanced atomic layer deposition (PEALD), and used as both an electron transport layer and hole blocking compact layer of perovskite solar cells. The metal precursors of tantalum ethoxide and titanium isopropoxide are simultaneously injected into the deposition chamber. The Ta content is controlled by the temperature of the metal precursors. The experimental results show that the Ta incorporation introduces oxygen vacancies defects, accompanied by the reduced crystallinity and optical band gap. The PEALD Ta-doped films show a resistivity three orders of magnitude lower than undoped TiO2, even at a low Ta content (0.8–0.95 at.%). The ultraviolet photoelectron spectroscopy spectra reveal that Ta incorporation leads to a down shift of valance band and conduction positions, and this is helpful for the applications involving band alignment engineering. Finally, the perovskite solar cell with Ta-doped TiO2 electron transport layer demonstrates significantly improved fill factor and conversion efficiency as compared to that with the undoped TiO2 layer.

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