How Transparent Oxides Gain Some Color: Discovery of a CeNiO₃ Reduced Bandgap Phase As an Absorber for Photovoltaics

In this work, we describe the formation of a reduced bandgap CeNiO₃ phase, which, to our knowledge, has not been previously reported, and we show how it is utilized as an absorber layer in a photovoltaic cell. The CeNiO₃ phase is prepared by a combinatorial materials science approach, where a library containing a continuous compositional spread of Ce_xNi_1-xO_y is formed by pulsed laser deposition (PLD); a method that has not been used in the past to form Ce-Ni-O materials. The library displays a reduced bandgap throughout, calculated to be 1.48-1.77 eV, compared to the starting materials, CeO₂ and NiO, which each have a bandgap of ∼3.3 eV. The materials library is further analyzed by X-ray diffraction to determine a new crystalline phase. By searching and comparing to the Materials Project database, the reduced bandgap CeNiO₃ phase is realized. The CeNiO₃ reduced bandgap phase is implemented as the absorber layer in a solar cell and photovoltages up to 550 mV are achieved. The solar cells are also measured by surface photovoltage spectroscopy, which shows that the source of the photovoltaic activity is the reduced bandgap CeNiO₃ phase, making it a viable material for solar energy.