Ming-Way Lee

Sodium antimony sulfide (NaSbS2): Turning an unexpected impurity into a promising, environmentally friendly novel solar absorber material

We present a novel absorber material—NaSbS2—for solar cells. NaSbS2 is formed as an unexpected byproduct in the chemical synthesis of Sb2S3. However, NaSbS2 has many attractive features for a solar material. Here single phase NaSbS2 nanoparticles were synthesized through solution processing. NaSbS2 semiconductor-sensitized solar cells were demonstrated for the first time. The best cell yielded Jsc = 10.76 mA/cm2, Voc = 0.44 V, FF = 48.6%, and efficiency η = 2.30% under 1 sun. At the reduced 0.1 sun, the η increased to 3.18%—a respectable η for a new solar material.

Ion exchange-prepared NaSbSe2 nanocrystals: electronic structure and photovoltaic properties of a new solar absorber material

We report the calculated electronic structure, syntheses and photovoltaic properties of a new ternary solar absorber material NaSbSe2. NaSbSe2 nanocrystals (NCs) have been prepared from a Na–Sb–S precursor by the solution-based Se2− anion exchange reaction. The Na–Sb–S precursor was grown on a TiO2 electrode using the successive ionic layer adsorption and reaction (SILAR) method. X-ray diffraction shows that the synthesized NaSbSe2 NCs have the same crystal structure as the NaSbS2 precursor with the diffraction angles significantly down-shifted. Energy-dispersive X-ray spectroscopy confirms the complete anion exchange and formation of the NaSbSe2 phase. First principles calculations show that the ordered NaSbSe2 structure resulting from the ion exchange synthesis is important for the performance. The NaSbSe2 NCs have an average size of ∼17 nm and a near-optimal optical band gap Eg of 1.48 eV that is lower than the NaSbS2 precursor. Liquid-junction NaSbSe2 quantum dot-sensitized solar cells (QDSSCs) were fabricated from the synthesized NaSbSe2 NCs for the first time. The best cell, prepared using the Au counter electrode and the polysulfide electrolyte, yielded an efficiency of 2.22%, a short current density of 1.31 mA cm−2, an open-circuit voltage of 0.30 V and a fill factor of 56.4% under the reduced light intensity of 10% sun. The external quantum efficiency (EQE) spectrum covers the spectral range of 300–900 nm with a maximum EQE of 75% at λ = 500 nm. The near-optimal Eg suggests that NaSbSe2 could be a potential material for solar cells. In addition, the ion exchange method can be extended to the preparation of many new metal selenide-based solar materials from their corresponding sulfides. These materials may show improved characteristics compared to samples with more disorder.

Eco-Friendly NaSbS2 Quantum Dot-Sensitized Solar Cells

Ternary sulfide NaSbS₂ is a low-cost, environment-friendly semiconductor that has rarely been studied. This paper demonstrates, for the first time, solid-state NaSbS₂ quantum dot-sensitized solar cells (QDSSCs). NaSbS₂ nanoparticles were synthesized using the sequential ionic layer adsorption reaction method. Solid-state QDSSCs were fabricated from the synthesized nanoparticles using spiro-OMeTAD as the hole-transporting electrolyte. The best cell yielded an efficiency of 1.27% under 1 sun. At the reduced light intensity <italic>I</italic>₀ of 10% sun, the efficiency increased significantly to 4.11% with an open-circuit voltage <inline-formula><tex-math notation=LaTeX>

Lead tin sulfide (Pb1-xSnxS) nanocrystals: A potential solar absorber material.

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Bi2S3 Liquid-Junction Semiconductor-Sensitized SnO2 Solar Cells

</tex-math></inline-formula> of 0.51xa0V, a short-circuit current density <italic>J</italic>_sc of 1.68 mA/cm², and a fill factor (FF) of 47.8%. A sublinear power law of <italic>J</italic>_sc∝ <italic>I</italic>₀^0.52 accounts for the large improvement in performance under low-light intensities because of the reduced carrier recombination. The external quantum efficiency (EQE) spectrum covered the spectral region of 300–750 nm with a maximum EQE value of 72% at <italic>λ</italic> = 450 nm. The present efficiency (4.11%) represents about 30% improvement over the best previous result (3.18%) of liquid-junction QDSSCs. The respectable efficiency indicates that NaSbS₂ shows potential as an efficient solar absorber material.

Enhanced Photovoltaic Performance in AgSbS2 Liquid-Junction Semiconductor-Sensitized Solar Cells

We present a new ternary semiconductor absorber material - Pb1-xSnxS - for solar cells. Pb1-xSnxS nanocrystals (NCs) were synthesized using the successive ionic layer adsorption reaction (SILAR) process. Energy-dispersive X-ray spectroscopy revealed the Sn ratio for a sample prepared with five SILAR cycles to be x=0.55 (i.e. non-stoichiometric formula Pb0.45Sn0.55S). The optical spectra revealed that the energy gap Eg of the Pb1-xSnxS NCs decreased with an increasing number of SILAR cycles n, with Eg=1.67eV for the sample with n=5. Liquid-junction Pb1-xSnxS quantum dot-sensitized solar cells were fabricated using the polysulfide electrolyte. The best cell yielded a short-circuit current density Jsc of 10.1mA/cm2, an open circuit voltage of 0.43V, a fill factor FF of 50% and an efficiency of 2.17% under 1 sun. The external quantum efficiency spectrum (EQE) covered a spectral range of 300-800nm with a maximum EQE of ∼67% at λ=650nm. At the reduced light of 0.1 sun, the efficiency increased to 3.31% (with a normalized Jsc=17.7mA/cm2) - a respectable efficiency for a new sensitizer. This work demonstrates that Pb1-xSnxS shows potential as a solar cell absorber.