Investigation of Electrical Parameters of Amorphous–Crystalline Silicon Heterojunction Solar Cells: Correlations Between Carrier Dynamics and S-Shape of Current Density–Voltage Curve

Abstract

We have analyzed a-Si:H(p)/a-Si:H(i)/c-Si(n) heterojunction silicon solar cell having the S-shaped current density–voltage characteristics with a low fill factor and open-circuit voltage, using quantum efficiency (QE) characterization technique under forward/reverse voltage and different light (blue, infrared, and white) bias conditions. The curvature of S-shape is sensitive to excitation light intensities because of modification in junction barrier potential (variation in quasi-Fermi levels splitting). With forward-bias voltage alone near/above S-shaped region, cell's QE is uniformly reduced because of reduction in junction field and dominance of barrier for collection of holes. However, with blue and white light at bias voltages close to S-shaped characteristics, a uniform improvement of QE in broad wavelength region is observed because of defects saturation at the junction interface and photoconductivity in the a-Si layers. With white light and voltage bias, cell's QE is anomalously improved and it has even crossed the QE response at no voltage/light bias conditions in the blue region because of defects saturation in a-Si:H layers, whereas under infrared light and voltage bias conditions defect saturation is not displayed in the QE because of carrier generation in a deeper region of the cell after crossing unabsorbed photons front region.