Electrochemical Deposition Of P-Type Cuprous Oxide Thin Films For Photovoltaic Applications
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Date
2017-03
Authors
Elfadill Elziber, Nezar Gassem
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Cuprous oxide Cu2O is a natural p-type metal-oxide semiconductor, considered to be the oldest well-known p-type semiconductors that exhibit rectifying behavior. The high resistivity of the intrinsic Cu2O material is a critical problem to fabricate efficient solar cell based on Cu2O. Doping of Cu2O by a suitable dopant element such as sodium (Na) may reduce its resistivity making it more favorable as solar cell material. In this study, a low-cost solution based electrochemical deposition (ECD) method was used to prepare p-type Cu2O films on Pt-coated Si and n-Si (100) substrates. The Cu2O growth rate and the film thickness can be estimated by monitoring of the transferred charge during the electrochemical deposition process. The study investigates the role of the deposition applied potential from (-340 to -550) mV vs. Ag/AgCl and the role of electrolyte pH (9, 10 and 11) on the growth of Cu2O film. It is found that the applied potential and electrolyte pH have a great impact on the crystal structure and morphology of Cu2O film. The results confirmed the growth of a pure phase of Cu2O when using applied potential between (-340 to -490) mV from an electrolyte having a pH above 8. The structure of the films deposited on Pt-coated Si was highly sensitive to the electrochemical deposition parameters compared to the films deposited on the bare Si substrate. It is found that the crystallographic growth direction of the prepared Cu2O can be controlled through these parameters to alter from (200), (110) and (111) orientations. Cu2O electrical characterizations showed a very high resistivity (104 -105) Ω.cm and a very low carrier concentration (1014 -1015) cm-3 for all films. A notable improvement in Cu2O electrical properties was achieved by the co-deposition of sodium Na element as a p-type dopant. The doping was achieved by adding a different amount of sodium alumina complex solution to the Cu(II) lactate electrolyte. The resistivity of the Na-doped Cu2O films deposited on both Pt-coated Si and n-Si substrate were lowered from 1.2×106 and 1.1×105 to 291 Ω.cm and 330 Ω.cm, respectively. Consequently, their free hole concentration was increased to be in the order of (≈1018) cm-3. Three p-n junction solar cells based on the optimized undoped and Na-doped p-type Cu2O films were fabricated as follows: p-Cu2O/n-Si and p-Cu2O/n-ZnO heterojunctions and p-n Cu2O homojunction with an active area 1 cm2, 1 cm2 and 0.6 cm2 respectively. J-V measurement confirms the formation of a rectifying junction on all built p-n junctions. Based on undoped p-Cu2O films, the best obtained conversion efficiency for p-Cu2O/n-ZnO and p-Cu2O/n-Si heterojunction solar cells and p-n Cu2O homojunction solar cells were 1.45 %, 0.058%, and 0.23% respectively. The conversion efficiency of the p-Cu2O/n-Si heterojunction solar cells was improved further from 0.058% to 0.31% by the introduction of Cu2O seed layer. In addition, the photovoltaic conversion efficiency of p-Cu2O/n-Si and p-Cu2O/n-ZnO heterojunction and p-n Cu2O homojunction solar cells fabricated based on the Na-doped Cu2O was improved to 0.45 %, 2% and 2.05% respectively.
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Keywords
Cuprous oxide Cu2O is a natural p-type , metal-oxide semiconductor