Crystallographic and Optical Properties of (Cu_1−xLi_x)₂SnS₃ Photovoltaic Semiconductor

Abstract

In order to clarify a lack of knowledge on lithium alloying with Cu2SnS3 (CTS), the authors synthesized monoclinic (Cu1–xLix)2SnS3 with 0.0 ≤ x ≤ 0.10 and characterized their crystallographic and optical properties. Their lattice constants, a, b, and c increased and angle β decreased with increasing Li content. Two band‐gaps (Eg1 and Eg2) are observed for the (Cu1–xLix)2SnS3 samples because there is a double onset in the diffuse reflectance spectra. The Eg1 almost linearly increases from 0.91 eV for x = Li/(Li + Cu) = 0.0 to 0.99 eV for x = 0.1 and the Eg2 also linearly increases from 0.99 eV for x = 0.0 to 1.10 eV for x = 0.1. To understand the band diagram of the (Cu1–xLix)2SnS3 solid solution, the energy level of the valence band maximum (VBM) from the vacuum level is determined from the ionization energy measured by photoemission yield spectroscopy (PYS). The energy levels of VBM for the (Cu1−xLix)2SnS3 solid solution monotonically decreases from −5.18 eV for x = 0.0 to −5.33 eV for x = 0.1 with increasing Li content. On the other hand, the energy levels of the conduction band minimum (CBM) is kept almost constant value by changing Li content. Therefore, the authors consider that the increase in the band‐gap energy of the (Cu1–xLix)2SnS3 solid solution is mainly caused by lowering the VBM level.

Formation of Native Inx(O,S)yBuffer through Surface Oxidation of Cu(In,Ga)(S,Se)2Absorber for Significantly Enhanced Conversion Efficiency of Flexible and Cd‐Free Solar Cell by All‐Dry Process

“…Figure a,b consequently demonstrates PYS spectra of the CIGSSe absorbers on flexible SUS substrates without and with air‐annealing process at 130 °C for 6 h. It is revealed in Figure 5a that near‐surface region of the CIGSSe absorber without the air‐annealing process, having small Ga content near CIGSSe surface, [ 39–41 ] is composed of CIGSSe and In 2 S 3 with E V values of about −5.2 and −6.1 eV, respectively. It has been reported that E V values of CuInSe 2 and CuInS 2 are about −5.2 and −5.5 eV, [ 42,43 ] as well as that of In 2 S 3 is in a range from about −6.0 to −6.2 eV. [ 44,45 ] In addition, the different E V between CIGSSe and In 2 S 3 (Δ E V ) is 0.9 eV in Figure 5a.…”

Nanopillar arrays of mesoporous Bi2Se3 and CuInSe2 in layer‐based perovskite solar cells

“…In Figure 1b,c the energy level diagram of FTO/ZnO/meso‐ Bi 2 Se 3 or CuInSe 2 : MAPbI 3 /Spiro_OMeTAD/Au configuration are shown. [41–43] The most important characteristic of ETL is its role in band alignment with the perovskite layer [44]. The energy level of CuInSe 2 is well‐aligned with other layers (CH 3 NH 3 PbI 3 and ZnO with a band‐gap of 3.44 eV [26, 45]), which lowers the driving force needed for electron injection from MAPbI 3 to CuInSe 2 [12].…”

“…In Figure 1b,c the energy level diagram of FTO/ZnO/meso-Bi 2 Se 3 or CuInSe 2 : MAPbI 3 /Spiro_OMeTAD/Au configuration are shown. [41][42][43] The most important characteristic of ETL is its role in band alignment with the perovskite layer [44].…”