Flexible supercapacitors exhibiting high specific energy (>1 mW h cm(-3)) and high specific power are of major research interest in energy storage/conversion systems. In this paper, a strategy has been developed for controlled synthesis of polypyrrole (PPy) nanofilms at the ice/alcohol interface through a simple chemical oxidation polymerization method, yielding free-standing PPy nanofilms with decimeter scale. Evidence from molecular dynamics simulations shows monolayer deposition of pyrrole molecules on the ice surface through hydrogen bonding that supports the formation of PPy films at the ice/alcohol interface. Free-standing PPy films can be directly tailored into film electrodes for all-solid-state flexible planar supercapacitor cells (PSCs) and rolled supercapacitor cells (RSCs). Thickness-dependent electrochemical performance for PSCs and RSCs has been constructed in association with PPy nanofilms. The PSCs and RSCs are made from complete PPy films with thickness of 140 +/- 5 nm that exhibit specific energy of 0.72 and 2.3 mW h cm(-3) with corresponding specific power of 51.7 and 111.1 mW cm(-3), respectively. After 10,000 cycles at a current density of 2 mA cm(-2), typical RSCs retain a volumetric capacitance of 9.8 F cm(-3) and a specific energy of 1.36 mW h cm(-3), holding great potential in practical applications. (C) 2017 Elsevier Ltd. All rights reserved.