Atomic layer deposition of energy band tunable tin germanium oxide electron transport layer for the SnS-based solar cells with 400 mV open-circuit voltage

Abstract

Tin germanium oxide, (Sn,Ge)O2, films were prepared using atomic layer deposition and tailored to a SnS absorber layer by incorporating various amounts of germanium into tin oxide to adjust band alignments at the interfaces of SnS/(Sn,Ge)O2 photovoltaic devices. Carrier concentrations of (Sn,Ge)O2 were suppressed from 1020 to 1018 cm−3 with germanium incorporation, with nitrogen doping further reducing carrier concentrations by another order of magnitude. Excellent tunability of both band energy levels and carrier concentrations of (Sn,Ge)O2 allowed optimizing SnS-based solar cells. SnS/(Sn,Ge)O2:N devices were demonstrated, with an open-circuit voltage as high as 400 mV, due to the effective mitigation of interfacial recombination of photogenerated carriers at the SnS/(Sn,Ge)O2:N absorber-buffer heterojunction interface.

SnS Homojunction Solar Cell with n‐Type Single Crystal and p‐Type Thin Film

“…In addition, Table 2 shows the detailed photovoltaic characteristics of the SnS solar cells, i.e., series resistance (R S ), shunt resistance (R Sh ), ideality factor of a diode (n), and the reverse saturation current (J 0 ), which were obtained from the J-V relationship of the single-junction solar cells (Section S2, Supporting Information), [29] together with the thickness of SnS layer (d). As shown in Table 2, the V OC of the homojunction solar cells fabricated in this study was remarkably high after the heterojunction solar cells fabricated by Pawar et al in 2020 ((V OC ¼ 405 mV with η ¼ 3.72%), [16] The properties of undoped SnS thin film are those of the film deposited on the SiO 2 glass substrate under the same conditions as the films deposited on the n-type SnS single crystals; b) The study by Kawanishi et al [22] Chua et al in 2019 ((V OC ¼ 400 mV with η ¼ 2.21%), [15] and Sinsermsuksakul et al in 2014 ((V OC ¼ 372 mV with η ¼ 4.4%). [13] To investigate the built-in potential (V bi ), acceptor and donor concentrations (N A and N D , respectively), and the depletion region of the n-type and p-type layers (w n and w p , respectively), the capacitance-reverse bias voltage (C-V ) characteristics were analyzed using Equation ( 1) and ( 2)…”

“…However, despite significant efforts to improve the V OC , the highest V OC is still limited to ≈400 mV, resulting in conversion efficiency ( η) of 2−4%. [ 15,16 ] A recent study reported a η of 4.8% with a V OC of 330 mV for a p‐SnS/n‐TiO 2 heterojunction, [ 17 ] which is the highest reported value for any SnS‐containing solar cells; however, this value is much lower than the theoretical value of SnS homojunction solar cell ( η = 25% at a V OC of 985 mV). [ 18 ] This implies that a further increase in the V OC of SnS heterojunction solar cell is considerably difficult.…”

“…For example, the CBO of the heterojunctions between p-type SnS and n-type CdS is À0.5 eV, [8] which results in a small V OC (<300 mV). [2,9,10] Interface band engineering, which involves the use of n-type materials such as Zn(O,S), [11,12] Zn(O,S):N, [13] Zn 1-x Mg x O, [14] (Sn,Ge)O 2 , [15] and (Zn,Cd)S [16] has been introduced as an effective method to modify the CBO of p-type SnS. However, despite significant efforts to improve the V OC , the highest V OC is still limited to %400 mV, resulting in conversion efficiency (η) of 2À4%.…”

Azimuthal angle dependent dielectric function of SnS by ellipsometry

“…Fig. 4 The critical point (CP) energies of SnS ε 2 , we fit the values in Table 1 with the cubic polynomial functions. The fit results are listed in Table 2.…”

“…Stack-layered structures materials in IV-VI group bring remarkable properties, which show high anisotropy of electrical and optical properties along with principal directions [1][2][3][4]. Strong correlation between the lattice anisotropy and optical property is indispensable information for many technological applications such as solar cells [5,6], ion batteries [7], sensors [8], thermoelectric devices [9], photovoltaics [10], and nonlinear optical applications [11][12][13][14].…”