Investigations in structural morphological and optical properties of Bi–Pb–S system thin films

Exploring the PbS–Bi2S3 Series for Next Generation Energy Conversion Materials

“…As hypothesized in the Introduction, the mixed phases between the highly dispersive electronic structure of PbS and the dense, yet less dispersive, electronic structure of Bi 2 S 3 could be expected to combine these two properties, both of which are particularly beneficial for photovoltaic applications. The high density of states and dense band structures in Figure are indicative of the latter in all of the mixed lead bismuth sulfides and are reflective of the high absorption coefficients found by Malika et al The band dispersion in each of the band structures, however, is variable, with Pb 3 Bi 2 S 6 , on a qualitative examination, displaying high local dispersion around the band edges, indicative of higher mobility, whereas Pb 2 Bi 2 S 5 has especially flat bands, particularly at the valence band maximum. To quantify this, the effective masses of both carriers were calculated for each of the five compounds, using a parabolic band approximation.…”

“…57−59 Electronic characterization, however, has been scarce: In 2013, Malika et al recorded the absorption coefficient and other optical properties of thin films of mixed PbS−Bi 2 S 3 : All of the films possessed high absorption coefficients (>1 × 10 5 cm −1 ) and variable band gaps within the 0.3−1.6 eV range bounded by PbS and Bi 2 S 3 , although they tended to cluster near the end points. 60 Ohta et al also recently considered two members of the series, Pb 3 Bi 2 S 6 and PbBi 2 S 4 , as potential thermoelectric materials, finding that both provided thermoelectric power factors of >2 μW K −2 cm −1 and zT of >0.25 at 700 K, all without tuning the carrier concentration to optimize zT. 61 These encouraging zT values were reasoned to be primarily due to low lattice thermal conductivities in all cases.…”

“…A significant amount of work on the isolation and structural characterization of natural members of the PbS–Bi 2 S 3 mixed series was performed in the 1960s and 1970s, in particular the work of Takéuchi and Takagi to refine Pb 6 Bi 2 S 9 (heyrovskyite), Pb 3 Bi 2 S 6 (lillianite), and PbBi 4 S 7 . More recently, Makovicky and co-workers reinvestigated the phase behavior of Pb 6 Bi 2 S 9 , Pb 3 Bi 2 S 6 , and PbBi 2 S 4 (galenobismutite), finding a number of high-pressure phases. − Electronic characterization, however, has been scarce: In 2013, Malika et al recorded the absorption coefficient and other optical properties of thin films of mixed PbS–Bi 2 S 3 : All of the films possessed high absorption coefficients (>1 × 10 5 cm –1 ) and variable band gaps within the 0.3–1.6 eV range bounded by PbS and Bi 2 S 3 , although they tended to cluster near the end points . Ohta et al also recently considered two members of the series, Pb 3 Bi 2 S 6 and PbBi 2 S 4 , as potential thermoelectric materials, finding that both provided thermoelectric power factors of >2 μW K –2 cm –1 and zT of >0.25 at 700 K, all without tuning the carrier concentration to optimize zT .…”

Structural and Optical Properties of Nanoscale Galinobisuitite Thin Films

“…The structural, morphological, and optical properties of the Bi–Pb–S system were investigated, since various compositions between the stable Bi 2 S 3 and PbS phases can be obtained. The differences in the crystallographic structure (orthorhombic for Bi 2 S 3 and cubic for PbS) and the absorption edges (in the visible region for Bi 2 S 3 and near infrared for PbS) constitute a sufficient argument to promote structural and optical investigations [5]. The material obtained was characterized by X-ray diffraction (XRD) and optical measurements, and the results are discussed in connection with the crystal structure of the film.…”