Vanadium oxide as a passivating-carrier selective contact for silicon heterojunction solar cell application
摘要
The potential of thermal evaporation-grown vanadium pentoxide (V2O5) as a passivating-carrier selective contact material for high-performance heterojunction crystalline silicon solar cells was examined in this work, with particular emphasis on the effects of film thickness from 1.5 nm to 4.5 nm on the characteristics of vanadium sub-oxide (V2Ox) thin films and their passivation characteristics on n-type c-Si (111) Cz wafers. V2Ox thin films were made by thermal evaporation at a chamber pressure of 5 × 10–5 mbar, with different film thicknesses. The findings give an insight into the effect of film thickness on the electrical and surface passivation capabilities of V2Ox films. With increasing layer thickness, electrical resistance was observed to rise while carrier concentration decreased, but a slight improvement in carrier mobility. The minority carrier lifetime values ranged from 64.07 ± 3.39 µs to 230 ± 4.30 µs and thicker films showed enhanced passivation. It is hypothesised that the formation of a sub-stoichiometric SiOx interlayer containing fixed charges adds to the field-effect passivation mechanism. The analysis revealed that a 4.5 nm thick V2Ox film had the best optoelectronic characteristics, an optical transmittance of above 90%, an electron concentration of 2.62 × 1013 cm−3 and a mobility of 40 cm2/V-s. This 4.5 nm thick V2Ox film as a passivation layer gives a minority carrier lifetime of 230 ± 4.30 µs and an implied open-circuit voltage (iVoc) of 652 ± 1 mV for a commercial n-type silicon wafer. A passivating contact solar cell has been fabricated for validating the passivation studies with an open-circuit voltage (Voc) of 627 mV. These results are important for developing heterojunction silicon solar cell technology.