Characterization of Transition Metal Oxide/Silicon Heterojunctions for Solar Cell Applications

Abstract

During the last decade, transition metal oxides have been actively investigated as hole-and electron-selective materials in organic electronics due to their low-cost processing. In this study, four transition metal oxides (V2O5, MoO3, WO3, and ReO3) with high work functions (>5 eV) were thermally evaporated as front p-type contacts in planar n-type crystalline silicon heterojunction solar cells. The concentration of oxygen vacancies in MoO3−x was found to be dependent on film thickness and redox conditions, as determined by X-ray Photoelectron Spectroscopy. Transfer length method measurements of oxide films deposited on glass yielded high sheet resistances (~10 9 Ω/sq), although lower values (~10 4 Ω/sq) were measured for oxides deposited on silicon, indicating the presence of an inversion (hole rich) layer. Of the four oxide/silicon solar cells, ReO3 was found to be unstable upon air exposure, while V2O5 achieved the highest open-circuit voltage (593 mV) and conversion efficiency (12.7%), followed by MoO3 (581 mV, 12.6%) and WO3 (570 mV, 11.8%). A short-circuit current gain of ~0.5 mA/cm 2 was obtained when compared to a reference amorphous silicon contact, as expected from a wider energy bandgap. Overall, these results support the viability of a simplified solar cell design, processed at low temperature and without dopants.

Parasitic Absorption Reduction in Metal Oxide-Based Transparent Electrodes: Application in Perovskite Solar Cells

“…[3][4][5] Their high work function, large band gap, efficient carrier selectivity, and high transparency make them viable and cost-effective candidates for these applications, where they are employed as protective buffer layers, 6-10 optical spacers [11][12][13] or charge transport layers. [14][15][16][17][18][19][20][21] TMOs are susceptible materials, which are sensitive to their environment, such as air or oxygen exposure, 22 temperature, [23][24][25][26] UV-light, 27 UV-ozone 28 or plasma treatments. [29][30][31][32][33] This is because many TMOs readily undergo redox reactions.…”

Silicon based solar cells using a multilayer oxide as emitter

“…So WAW multilayer exhibits better surface passivation performance and higher V oc potential over WO 3 layer. The real V oc measured from light J-V curves in this work seems 150 mV lower than the typical WO 3 /n-Si solar cells with a V oc of ∼570 mV, 13,15 which is largely due to the absence of back surface field (BSF) and surface passivation. Fig.…”

“…17 Whereas TMOs are sensitive to temperature significantly, the post-deposition anneal may impair their (MoO 3 and V 2 O 5 ) high work-function and carrier selectivity, resulting in the degradation of FF as well as PCE. 11,13,16 Here, we incorporate oxide/metal/oxide (OMO) multilayer into silicon based solar cells as emitter, charge-carriers lateral transportation and collection are achieved through inserting one thin metal film into TMOs. OMO multilayer, such as MoO 3 /Ag/MoO 3 (MAM), 18 22 has been developed as transparent electrode in organic devices due to high-transmittance, low-resistivity and low-damage deposition.…”

“…However, several limitations of SHJ solar cells may restrict its practical application, such as explosive dopant-gas precursors and costly film deposition equipment. Since transition metal oxides (TMOs), compromising MoO 3 , WO 3 , V 2 O 5 and TiO 2 , show the merits of highly transparent, selective charge extraction and facile deposition, 2-9 they are explored extensively as candidates for substituting boron/phosphorous doped a-Si:H. [10][11][12][13] In the last few years, MoO 3 , WO 3 , V 2 O 5 with nm-thickness capped directly on n-type silicon (n-Si) show extraordinary hole-selectivity, 14,15 which favour charge-carriers' separation by transporting holes while blocking electrons, and reaching the efficiency of 14.3% for MoO x /n-Si heterojunctions. 14 Moreover, when inserting an intrinsic a-Si:H layer into MoO x /n-Si heterojunctions for passivation, PCE as high as 22.5% has been recorded for this novel structure (MoO x /a − Si:H/n-Si) solar cells.…”

12.29% Low Temperature–Processed Dopant‐Free CdS/p‐Si Heterojunction Solar Cells

“…Recently, low temperature–processed carrier selective contacts were demonstrated by several material systems (having a considerably larger band gap than a‐Si:H) on n‐Si wafers. Sub‐stoichiometric transition metal oxides such as nickel oxide (NiO x ), tungsten oxide (WO x ), molybdenum oxide (MoO x ), and vanadium oxide (VO x ) generally have a wide band gap ( E g > 3 eV) and high work‐function (φ ≥ 5.2 eV). They can be easily thermally evaporated or spin‐coated onto the surface of c‐Si wafer to form excellent hole selective contact.…”