Antimony Selenide Absorber Thin Films in All-Chemically Deposited Solar Cells

Abstract

Chemically deposited antimony selenide ͑Sb 2 Se 3 ͒ thin film has a coexisting antimony oxide ͑Sb 2 O 3 ͒ phase which may be converted to crystalline Sb 2 Se 3 thin films with an optical bandgap of 1.13 eV when heated at 300°C in nitrogen in the presence of selenium vapor. Instead of this, if the heating is done with an Sb 2 S 3 thin film on the chemically deposited Sb 2 Se 3 :Sb 2 O 3 thin film, a solid solution with the coexisting oxide phase ͑Sb 2 Se 3−x S x :Sb 2 O 3 ͒ is produced. The optical bandgap of such absorber material is 1.34-1.58 eV. The as-deposited thin films as well as those produced by heating are photoconductive. They were incorporated into solar-cell structures developed entirely by chemical deposition on SnO 2 :F-coated commercial transparent conductive oxide ͑TCO͒ glass. The cell structure, TCO/CdS/Sb 2 Se 3 :Sb 2 O 3 /PbS, showed an open-circuit voltage ͑V oc ͒ of 540 mV and short-circuit current density ͑J sc ͒ of 0.67 mA/cm 2 . In the cell TCO/CdS/Sb 2 Se 3−x S x :Sb 2 O 3 /PbS produced by heating in nitrogen, V oc is 520 mV, J sc is 4.2 mA/cm 2 , and conversion efficiency ͑͒ is 0.66%. The scalability of the all-chemically deposited solar cell is demonstrated in four series-connected cells of area 1 cm 2 each, showing short-circuit current of 1.5 mA and V oc of 1.9 V under sunlight.

A comparative study on the electronic and optical properties of Sb-=SUB=-2-=/SUB=-Se-=SUB=-3-=/SUB=- thin film

“…5, g), respectively. Table 2 it is clear that the obtained direct band gap is in good agreement with SE and UV-vis as well as reported values [26,[33][34][35][36] while indirect band gap is consistent with UV-vis, theoretical and the reported values [35,36,38]. However, the theoretical value is a little bit smaller than the experimental values due to exchange correlation [53] and the formation of nanocrystalline after annealing could be introduced quantum size effect.…”

“…Although, Sb 2 Se 3 is used in various fields, the lack of proper knowledge regarding its electronic structure and optical properties sometimes leads to contradictory interpretations of the experimental data found in literature [26]. Regarding the direct/indirect band gap nature a few contradictory reports are available in literature: 1.0 to 1.82 eV for single crystals [27][28][29][30][31], for thin films direct (1.5−2.14) eV [32][33][34], indirect transitions (1−1.2) eV [35][36][37][38][39], and the theoretical indirect band gap energy of 1.21 eV using density functional theory (DFT) within the obtained gradient approximation (GGA) with GW corrections [26], as well as 0.99 eV (indirect)−1.07 eV (direct) obtained using DFT with LDA [40].…”

Band gap temperature-dependence of close-space sublimation grown Sb2Se3 by photo-reflectance

“…Variable material quality is another key factor complicating band gap assessment. Amorphous material is often reported [7][8][9]11,18,25,26 in low-temperature Sb 2 Se 3 deposition and always has a higher gap than crystalline material. An amorphous-to-crystalline transition 7,8,11,16,26,31 occurs upon annealing above 200 • C, yet while crystalline material is easily detected by x-ray diffraction, amorphous phase fractions are more difficult to quantify.…”

“…Amorphous material is often reported [7][8][9]11,18,25,26 in low-temperature Sb 2 Se 3 deposition and always has a higher gap than crystalline material. An amorphous-to-crystalline transition 7,8,11,16,26,31 occurs upon annealing above 200 • C, yet while crystalline material is easily detected by x-ray diffraction, amorphous phase fractions are more difficult to quantify. In non-stoichiometric material, the band gap is reported to increase quadratically with increasing Se content 26 or in the presence of an oxygen impurity 5,7 (perhaps differing from the Fd3m Sb 2 O 3 phase) which is removed after annealing in N 2 and Se vapor at 300 • C. Allowing also for potential polycrystalline disorder, each of these factors likely necessitates the consideration of an Urbach tail in any fit to the absorption onset.…”

“…An amorphous-to-crystalline transition 7,8,11,16,26,31 occurs upon annealing above 200 • C, yet while crystalline material is easily detected by x-ray diffraction, amorphous phase fractions are more difficult to quantify. In non-stoichiometric material, the band gap is reported to increase quadratically with increasing Se content 26 or in the presence of an oxygen impurity 5,7 (perhaps differing from the Fd3m Sb 2 O 3 phase) which is removed after annealing in N 2 and Se vapor at 300 • C. Allowing also for potential polycrystalline disorder, each of these factors likely necessitates the consideration of an Urbach tail in any fit to the absorption onset. 26 Band gap temperature evolution (arising from thermal lattice expansion and the electronphonon interaction) 32,33 may have significant photovoltaic implications: with efficiencies falling by as much as 0.1% K 1 as reverse saturation current and band gap reduction each increase with temperature.…”