All-oxide photovoltaics by cost-effective chemical routes

2018 edition

Pamela Machado, Estel Rueda

Nowadays, the 90% of the photovoltaic (PV) market is constituted by silicon-based devices, but they still require some improvements: decrease the energy payback time and the difficulty to achieve power conversion efficiencies (PCE) beyond the thermodynamic limit (32%). So, alternative technologies with cheap components with potential for higher PCE are being studied. An all-oxide PV approach is very appealing due to the chemical, mechanical and thermal stability, non-toxicity and abundance of many metal oxides that allow preparation by cost-effective and scalable techniques. In particular, ferroelectric perovskite oxides (FEPO) have recently emerged as a potential alternative to conventional semiconductor absorbers for the fabrication of efficient solar cells. FEPO present a permanent electrical polarization that can affect the PV mechanism and an abnormal PV effect that could lead PCE beyond the thermodynamic limit. Multiferroic Bi-based perovskite oxides such as BiFeO3 (BFO) are focusing great deal of attention because room temperature ferroelectricity, magnetism and light absorption phenomena can be coupled leading to new challenges and avenues in PV.

Here, we take advantage of a low-cost and versatile chemical solution deposition (CSD) technique to study the stabilization of new compositions based on BFO for visible-light absorption. The influence of processing temperature, time and atmosphere has been investigated on the formation of BiFe1-xCoxO3 (BFCO) thin films. Advanced X-ray diffraction characterization and atomic-resolution imaging of cation-doped BFCO thin films demonstrate the successful incorporation of cobalt atoms in the BFO structure resulting epitaxial thin films. For the first time we present BiFe1-xCoxO3 (BFCO) thin films with modulated bandgap, from 2.7 eV (UV) to 1.4 eV (visible) films while preserving the ferroelectric behavior. Finally, the optimized CSD processing conditions for the BFCO thin films have been proved compatible on several oxide bottom electrodes: La0.7Sr0.3MnO3 and ITO layers, being thus a promising strategy to build all-oxide-base multilayered structure for PV.