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

• Published in: Applied sciences Vol. 5; no. 4; pp. 695 - 705
• Main Authors: Gerling, Luis, Mahato, Somnath, Voz, Cristobal, Alcubilla, Ramon, Puigdollers, Joaquim
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01-12-2015
• Subjects: Air exposure; Amorphous silicon; Cost reduction; Electrodes; Film thickness; Heterojunctions; Lattice vacancies; Low temperature; Materials selection; Metal oxides; molybdenum oxide; Molybdenum trioxide; Open circuit voltage; Oxide coatings; Oxides; Photoelectron spectroscopy; Photoelectrons; Photovoltaic cells; rhenium oxide; Semiconductors; Short circuit currents; Short-circuit current; Silicon; silicon heterojunction solar cells; Solar cells; Spectrum analysis; Transition metal oxides; tungsten oxide; vanadium oxide; Work functions; United Kingdom > UK; England; United States > US
• ISSN: 2076-3417; 2076-3417
• DOI: 10.3390/app5040695

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 (~109 Ω/sq), although lower values (~104 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/cm2 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.