In this work, an easy low-temperature (＜100 °C) solution-chemical technique was demonstrated to prepare solar absorber coatings containing nanogold. Using poly(urethane) (PU) as the binder, gold/copper chloride composite coatings were directly formed on copper substrates via the redox reactions of HAuCl4 and copper. HAuCl4 concentration in the coating solution was kept as low as possible, and a doctor-blade method was employed. The heating performance of each prepared coating was tested by irradiating with simulated sunlight and was dependent on the weight ratio of PU/HAuCl4 in the coating solution. Although solar absorptance can be more than 0.92 when the HAuCl4 concentration in the coating solution was increased, a coating prepared from the solution containing 0.003 M HAuCl4 and an equal weight of PU gave the best heating performance. Solar absorptance and thermal emittance of this coating were 0.846 and 0.09, respectively. The results of X-ray diffraction showed that the top surface of the coating was abundant in CuCl2 while the bottom surface was abundant in CuCl and Au. The grain sizes of Au as calculated by Scherrer equation was 3–4 nm.
