Ultrathin crystalline silicon (c-Si) solar cells represent an important technology development direction for reducing material usage and thus lowering the cost of solar electricity. Here, we demonstrate a prototype device with high efficiency assisted by a micro-/nano-structured polycarbonate thin nanofur film inspired by water ferns. The ultrathin c-Si solar cells consist of a 17 mu m-thick c-Si absorber and exhibit an efficiency of up to 17.3% and short-circuit current density (J(sc)) of 35.8 mA cm(-2). With the assistance of the thin nanofur, the efficiency is increased to 18.1% due to an increase in J(sc) to 37.4 mA cm(-2). The photocurrent enhancement is attributed to, firstly, a more favorable refractive index transition due to the polymer addition and, secondly, the high forward scattering of the structured film, which increases the optical pathlength within the ultrathin absorber layer of the devices. To our knowledge, the present prototype device demonstrates the highest J(sc) and efficiency in the area of ultrathin c-Si solar cells with an absorber layer of less than 20 mu m.