Hideaki Araki

Fabrication of Cu2SnS3 thin-film solar cells with power conversion efficiency of over 4%

Cu2SnS3 (CTS) thin films were produced by the co-evaporation of Cu, Sn, and cracked sulfur, followed by annealing. The as-deposited films were then annealed at 570 °C for 5 min in the presence of 100 mg of sulfur lumps in a rapid thermal processing furnace filled with N2 gas at atmospheric pressure. Solar cells were then fabricated using the CTS films as absorber layers, and their efficiency was evaluated for different Cu/Sn compositional ratios. The largest grain size was found for films with a slightly Sn-rich composition. The highest performance was obtained for solar cells containing a CTS thin film with a Cu/Sn ratio of about 1.9. A cell with a Cu/Sn ratio of 1.87 exhibited an open-circuit voltage of 258 mV, a short-circuit current density of 35.6 mA/cm2, a fill factor of 0.467, and a power conversion efficiency of 4.29%.

Cu2SnS3 Thin-Film Solar Cells from Electroplated Precursors

Cu2SnS3 (CTS) contains non-rare metals and it has suitable optical characteristics for the absorber layer of thin-film solar cells. In this study, CTS thin films were fabricated by sulfurizing Cu?Sn precursors deposited by co-electrodeposition. Solar cells with a structure glass/Mo/CTS/CdS/ZnO:Al/Al were fabricated from the films. The best cell had an efficiency of 2.84%. A relatively high conversion efficiency was obtained from films with Cu/Sn?2.

Sulfurization temperature dependences of photovoltaic properties in Cu2SnS3-based thin-film solar cells

We report on the sulfurization of metal-alloyed precursors in Cu2SnS3 (CTS)-based thin-film solar cells. CTS thin films were prepared through the sulfurization of Cu?Sn alloy precursors at sulfurization temperatures of 500?580 ?C for 2 h in a N2 atmosphere with sulfur vapor. The Cu/Sn composition ratios of the sulfurized films were determined by X-ray fluorescence analysis to be in the range of 1.77?1.89. The photovoltaic properties of CTS-based solar cells improved with increasing sulfurization temperature owing to the higher external quantum efficiency at long wavelengths. The solar cell comprising a CTS thin film with a sulfurization temperature of 580 ?C exhibited the optimum performance among the cells examined: an open-circuit voltage of 244 mV, a short-circuit current density of 29 mA/cm2, a fill factor of 0.385, and a conversion efficiency of 2.7% were obtained.

Preparation of Cu2SnS3 Thin Films by Sulfurization of Cu/Sn Stacked Precursors

Cu2SnS3 (CTS) has been reported to have various band gap energies in the range of 0.93–1.77 eV and an absorption coefficient of 1.0×104 cm-1. It consists of elements that are inexpensive due to their abundance in Earths crust. Consequently, CTS is expected to be utilized in the absorber layers of thin-film solar cells. In this study, Cu/Sn stacked-layer thin-film precursors were deposited on glass and glass/Mo substrates by electron beam evaporation. CTS thin films were fabricated by sulfurizing the precursors at temperatures of 450–580 °C for 2 h in an atmosphere of N2 and sulfur vapor. CTS films were estimated to have band gap energies of 0.96–1.00 eV by extrapolation. A solar cell fabricated using a CTS thin film sulfurized at 580 °C exhibited an open-circuit voltage of 211 mV, a short-circuit current of 28.0 mA/cm2, a fill factor of 0.43, and a conversion efficiency of 2.54%.

Fabrication of Cu2GeS3-based thin film solar cells by sulfurization of Cu/Ge stacked precursors

In- and Se-free Cu2GeS3 thin films were prepared by thermal evaporation followed by sulfurization, and photovoltaic cells with a glass/Mo/Cu2GeS3/CdS/ZnO:Al/Al structure were fabricated. The composition ratios of the obtained films were Cu/Ge = 1.96 and S/metal = 0.92 on glass, and Cu/Ge = 2.08 and S/metal = 0.94 on a Mo-coated glass substrate. By X-ray diffraction measurement, the sulfurized films were identified to be Cu2GeS3. By optical measurement, the band gap energy was estimated to be 1.5–1.6 eV. In the visible region, a Cu2GeS3 film has an optical absorption coefficient that is on the order of 104 cm−1. A solar cell fabricated using the Cu2GeS3 thin film exhibited an open-circuit voltage of 380 mV and a conversion efficiency of 1.70%.

Donor-acceptor pair recombination luminescence from monoclinic Cu2SnS3 thin film

The defect levels in Cu2SnS3 (CTS) were investigated using photoluminescence (PL) spectroscopy. A CTS thin film was prepared on a soda-lime glass/molybdenum substrate by thermal co-evaporation and sulfurization. The crystal structure was determined to be monoclinic, and the compositional ratios of Cu/Sn and S/Metal were determined to be 1.8 and 1.2, respectively. The photon energy of the PL spectra observed from the CTS thin film was lower than that previously reported. All fitted PL peaks were associated with defect related luminescence. The PL peaks observed at 0.843 and 0.867 eV were assigned to donor-acceptor pair recombination luminescence, the thermal activation energies of which were determined to be 22.9 and 24.8 meV, respectively.

Fabrication of lead halide perovskite solar cells by annealing spin-coated PbI2 thin films in CH3NH3I vapor

Lead halide perovskite (CH3NH3PbI3) solar cells possess numerous useful properties, such as appropriate direct bandgaps and high absorption coefficients, and these cells have recently attracted considerable attention owing to their excellent photovoltaic performance and low cost. In this study, perovskite layers intended for use as light-absorbing materials were fabricated by annealing spin-coated PbI2 thin-films in CH3NH3I vapor while assessing the effects of varying the annealing temperature. X-ray diffraction analysis indicated that perovskite began to form at temperatures above 140 °C, with the PbI2 peak completely disappearing above 160 °C. In addition, scanning electron microscopy observations confirmed that the grain size increased with increasing annealing temperature. Solar cells fabricated using perovskite thin-films grown at 140–150 °C for 4 h exhibited a power conversion efficiency of more than 4%.