Ultrathin c-Si solar cells ( <= 50 mu m) are believed to be applied in military, aerospace and other special circumstances in the future due to their flexibility and high specific power density, and thus has attracted a great deal of research interest. However, until now, lacking fabrication means of high-quality ultrathin c-Si materials accompanied with their inefficient absorption of near-infrared light greatly limits their further application. In this work, we present a simple and novel method to realize rapid thinning and texturing of bulk c-Si at room temperature by varying the rho ([HF]/([HF] + [H(2)O2])) values during the one-step Cu-assisted chemical etching process, followed by a systematic investigation of the formation mechanism of the surface structures. It is found that the sizes of surface structures accompanied with the etching rate increase with increasing the rho values from 40% to 95% during the double sided etching process, and a high etching rate of 29.6 gm/min is obtained under the rho value of 95%. For rapid thinning and efficient absorption of near-infrared light, 45 mu m c-Si solar cell with asymmetric front and back light trapping structures is rapidly fabricated by directly immersing as-sawn bulk c-Si substrate into the thinning (rho = 95%) and texturing (rho = 60%) solution successively for only a few minutes. A high short-current density (Jsc) (36.12 mA/cm(2)) and energy-conversion efficiency (17.3%) are achieved, which are 1.09 mA/cm(2) and 0.4% higher respectively than that in 45 mu m c-Si with flat back surface. Based on the absorption spectra, it is demonstrated that the 45 mu m c-Si cell with our asymmetric structures yields a high theoretical Jsc of 42.47 mA/cm(2), which nearly approaches the Yablonovitch limit of 42.56 mA/cm(2). All the findings offer additional insight into the structure formation mechanism and pave a rapid and novel way for exploration of next-generation flexible photovoltaics.