Effects on external quantum efficiency of electrochemically constructed n-ZnO/p-Cu2O photovoltaic device by annealing

Cuprous oxide (Cu2O), a terrestrial abundant, low cost, nontoxic, intrinsically p-type oxide semiconductor with bandgap energy of about 2eV, has recently received increasing attention as a light absorbing layer in solar cells. However, the performances of electrochemically constructed Cu2O solar devices are poor compared to the theoretical power conversion efficiency. This research was conducted focusing on the EQE performance, which is closely related to the short circuit current of a solar device. ZnO/Cu2O-PV-devices were constructed electrochemically with 3-electrode cell on Ga:ZnO/SLG substrates; ZnO layers were deposited from an aqueous solution of 8 mmolL(-1) zinc nitrate hexahydrate at 63 degrees C, 0.01 Coulomb cm(-2), and -0.8V, while Cu2O layers were deposited from aqueous solution containing 0.4 molL(-1) copper (II) acetate monohydrate (pH12.5), at 40 degrees C, 1.5 Coulomb cm(-2), and -0.4V. Devices were then annealed under different temperatures of 150 degrees C, 200 degrees C, 250 degrees C, and 300 degrees C for 60 minutes with a Rapid Thermal Anneal furnace (RTA). The EQE of the devices were measured with a spectral sensitivity device and compared to the non-annealed device. Further studies were made such as morphology observation of the films by FE-SEM and measurements of X-ray diffraction patterns. Annealed samples showed improved maximum EQE at 150-200 degrees C of annealing, indicating that EQE above 90% can be achieved, proving the validity of EQE improvement via low temperature annealing method for thin film Cu2O photovoltaic devices.