A novel method for preparing a luminescent solar concentrator (LSC) with fluorescent aqueous layer sandwiched between two pieces of flat glass is developed. By this method, an aqueous layer concentrator with a size of 78×78×7 (mm) is fabricated. After coupled with silicon solar cell, the concentrator shows a power conversion efficiency of 3.9%, about 30% higher than that of the same sized laminated glass concentrator employing the same dyes. Furthermore, the measured efficiency almost reaches the calculated limit of the aqueous layer LSC. This kind of aqueous layer LSC offers a potential application in the building-integrated photovoltaics.