ZnO based homojunction p-i-n solar cell to self-power UV detector

A simple novel and low cost efficient all ZnO based homojunction p-i-n solar cell without any top transparent conductive oxide layer and aback reflector layer are numerically modeled using 2D device simulation tool ATLAS. Optimization of the different layers, doping level and power conversion efficiency of the model has been done. The spectral response such as transmissivity, reflectance, and absorptance under AM1.5 solar illumination is well studied. Although the ZnO material responds to only a small portion of sunlight in UV region of AM1.5, the External Quantum efficiency(EQE) of the model is found to be nearly 70% and efficiency upto 16% for 1000nm thick i-layer ZnO. These optimized results are validated with other reported published experimental works. The wavelength dependent photo response properties of the homojunction are investigated in detail by studying the effect of light illumination on current-voltage (I-V) characteristics, photocurrent and spectral response at room temperature. From the photocurrent spectra, it is observed that the ultraviolet (UV)photons are absorbed in the depleted n-ZnO under positive bias conditions with responsivity of 1.6 mA/V. This indicates that such a model of ZnO p-i-n thin film homojunction can be used to sense UV though the photo response for UV as well as generate a significant energy to self-power this sensor.