Cubic Germanium monochalcogenides (π-GeS and π-GeSe): Emerging materials for optoelectronic and energy harvesting devices

Interfacial Strain Engineering in Wide-Bandgap GeS Thin Films for Photovoltaics

“…The bandgap of GeS was further calculated to be 1.7 eV using the equation (α h ν) 1/2 = A ( h ν – E g ) (Figure b), where A is a constant, h is the Planck’s constant, and ν is the frequency of incident photon . This value is in agreement with previous reports − and shows the great potential of GeS for top cells in tandem solar cells and IPVs.…”

“…We then calculated the stress (σ) in GeS film using the equation: where E p is the modulus of GeS, υ p is the Poisson’s ratio in GeS, α s and α f are the thermal expansion coefficients of substrate and GeS, respectively, and Δ T is the temperature difference between the annealing temperature and room temperature. Figure b shows the annealing temperature-dependent stress in GeS arising from the large thermal expansion mismatch between Mo (0.48 × 10 –5 K –1 ) and GeS (3.1 × 10 –5 K –1 ).…”

“…We turned our attention to germanium monosulfide (GeS), a simple binary semiconductor with a wide bandgap of 1.6–1.7 eV. − In contrast with its counterpart GeSe with a narrow bandgap of 1.14 eV, the bandgap of GeS is too wide for single-function solar cells but is optimal for indoor light harvesting and top cells in tandem devices. Furthermore, GeS has a high optical absorption coefficient (greater than 10 4 cm –1 ) and a high carrier mobility (about 86 cm 2 V –1 s –1 ). , It also exhibits great stability in ambient atmosphere, and the composition elements of Ge and S are low-toxic and earth-abundant. − All these attributes indicate the great potential of GeS for wide-bandgap solar cells.…”

Solution-processed Ge(ii)-based chalcogenide thin films with tunable bandgaps for photovoltaics

“…The bandgap of GeS lms is further calculated to be 1.71 eV by plotting (ahn) 1/2 versus (hn). The above optical results are consistent with the previous reports based on GeS, 52,53 further demonstrating the pure-phase of our solution-processed GeS lms.…”

Elucidating the role of lattice thermal conductivity in π‐phases of IV‐VI monochalcogenides for highly efficient thermoelectric performance

“…Generally, first-principles phonon calculations are used for obtaining sound velocities which are necessary for Cahill-Pohl model. However, for this study, we obtain these values from elastic properties of these cubic chalcogenides MX(M = Sn, Ge, X = S, Se) from our recently published articles 29,47,48 which were based on well-known Voigt-Reuss-Hill approximation. 102 Table 2 We have determined all the required transport coefficients which are essential to calculate the value of figures of merit (ZT) by the relation ZT = S 2 σ/(K e + K l ) for four types of cubic polymorphs (p-and n-type) against carrier concentration (at 300 and 800 K).…”