Atomic layer deposition of vanadium oxide films for crystalline silicon solar cells.

Transition metal oxides (TMOs) are promising materials to develop selective contacts on high-efficiency crystalline silicon solar cells. Nevertheless, the standard deposition technique used for TMOs is thermal evaporation, which could add potential scalability problems to industrial photovoltaic fabrication processes. As an alternative, atomic layer deposition (ALD) is a thin film deposition technique already used for dielectric deposition in the semiconductor device industry that has a straightforward up scalable design. This work reports the results of vanadium oxide (V2O5) films deposited by ALD acting as a hole-selective contact for n-type crystalline silicon (c-Si) solar cell frontal transparent contact without the additional PECVD passivating layer. A reasonable specific contact resistance of 100 mΩ cm2 was measured by the transfer length method. In addition, measurements suggest the presence of an inversion layer at the c-Si/V2O5 interface with a sheet resistance of 15 kΩ sq-1. The strong band bending induced at the c-Si surface was confirmed through capacitance-voltage measurements with a built-in voltage value of 683 mV. Besides low contact resistance, vanadium oxide films provide excellent surface passivation with effective lifetime values of up to 800 µs. Finally, proof-of-concept both-side contacted solar cells exhibit efficiencies beyond 18%, shedding light on the possibilities of TMOs deposited by the atomic layer deposition technique.

Transition-Metal Oxides for Kesterite Solar Cells Developed on Transparent Substrates.

Fabrication on transparent soda-lime glass/fluorine-doped tin oxide (FTO) substrates opens the way to advanced applications for kesterite solar cells such as semitransparent, bifacial, and tandem devices, which are key to the future of the PV market. However, the complex behavior of the p-kesterite/n-FTO back-interface potentially limits the power conversion efficiency of such devices. Overcoming this issue requires careful interface engineering. This work empirically explores the use of transition-metal oxides (TMOs) and Mo-based nanolayers to improve the back-interface of Cu2ZnSnSe4, Cu2ZnSnS4, and Cu2ZnSn(S,Se)4 solar cells fabricated on transparent glass/FTO substrates. Although the use of TMOs alone is found to be highly detrimental to the devices inducing complex current-blocking behaviors, the use of Mo:Na nanolayers and their combination with n-type TMOs TiO2 and V2O5 are shown to be a very promising strategy to improve the limited performance of kesterite devices fabricated on transparent substrates. The optoelectronic, morphological, structural, and in-depth compositional characterization performed on the devices suggests that the improvements observed are related to a combination of shunt insulation and recombination reduction. This way, record efficiencies of 6.1, 6.2, and 7.9% are obtained for Cu2ZnSnSe4, Cu2ZnSnS4, and Cu2ZnSn(S,Se)4 devices, respectively, giving proof of the potential of TMOs for the development of kesterite solar cells on transparent substrates.