Yuki Takiguchi

Device simulation of cuprous oxide heterojunction solar cells

We developed a device simulation model of cuprous oxide (Cu2O)-based heterojunction solar cells. The developed model well reproduces the reported experimental current density–voltage characteristics and the external quantum efficiency results. By using the model, we explored structures for high-efficiency Cu2O-based heterojunction solar cells. It was found that the electron affinity of the buffer layer between transparent conducting oxide and Cu2O significantly affects solar cell performance. Surface recombination on the rear side of the device can be suppressed by employing a highly doped back surface layer. Our device simulation demonstrates a conversion efficiency of 16% without any optical confinement structure.

Heterojunction p-Cu2O/n-Ga2O3 diode with high breakdown voltage

Heterojunction p-Cu2O/n-β-Ga2O3 diodes were fabricated on an epitaxially grown β-Ga2O3(001) layer. The reverse breakdown voltage of these p-n diodes reached 1.49 kV with a specific on-resistance of 8.2 mΩ cm2. The leakage current of the p-n diodes was lower than that of the Schottky barrier diode due to the higher barrier height against the electron. The ideality factor of the p-n diode was 1.31. It indicated that some portion of the recombination current at the interface contributed to the forward current, but the diffusion current was the dominant. The forward current more than 100 A/cm2 indicated the lower conduction band offset at the hetero-interface between Cu2O and Ga2O3 layers than that predicted from the bulk properties, resulting in such a high forward current without limitation. These results open the possibility of advanced device structures for wide bandgap Ga2O3 to achieve higher breakdown voltage and lower on-resistance.

Fabrication and characterization of sputtered Cu2O:N/c-Si heterojunction diode

Nitrogen doped cuprous oxide (Cu2O:N) deposited by reactive sputtering was applied to a crystalline silicon (c-Si) based heterojunction diode. The current density–voltage (J–V) characteristics of the fabricated diode showed rectifying characteristics with a high rectifying ratio of 105 at ±1 V. The capacitance–voltage measurements revealed the existence of a large conduction band offset and a small valence band offset at the Cu2O:N/c-Si interface, which implies that Cu2O:N is a suitable material for a hole selective emitter layer in n-type c-Si based heterojunction solar cells. Detailed analysis of the temperature dependent J–V characteristics showed that the diode current was limited by interface recombination originated from Fermi level pinning at the Cu2O:N/c-Si interface.