J - V curves, external quantum efficiency (EQE), and reflection spectra of a CNT/Si thin film. (a) Dark and light J-V curves of a CNT/Si (20 μm) thin-film solar cell with and without HNO3 doping. (b) Light J-V curves of CNT/Si thin-film cells made from Si thin film with various thicknesses. (c) EQE of CNT/Si thin-film solar cells made from 100- and 20-μm-thick Si films. (d) Reflection spectra of Si thin film and corresponding CNT/Si solar cells.