Absorption coefficient dependent non-linear properties of thin film luminescent solar concentrators

This research article studied absorption coefficient dependent losses and efficiency of thin film luminescent solar concentrator (LSC). The optimum absorption coefficient was determined by fabricating red dye doped thin film LSCs with varying absorption coefficients of 24-202 cm(-1). The optical, electrical, and ray-trace model predicted results were compared to establish the optimum absorption coefficient for fabricated thin film LSCs. The optical and electrical efficiencies of thin film LSCs are a function of absorption coefficient; follow linearly at lower values, gradually becoming non-linear at higher values of absorption coefficient which restricts the overall efficiency. The multi layered ray-trace model predicted results deviated from the experimental results at high absorption coefficient. Non-linearity was introduced by losses mechanism of re-absorption, resonant energy transfer (RET), and scattering in thin film LSCs. Re-absorption losses were found to be dependent on optical path length and absorption coefficient of thin film. They were identified and quantified through locally collected emission and optical path-length in thin film LSCs. Re-absorption losses caused a red shift in emission peak by approximate to 20 nm as the absorption coefficient increased from 24 to 202 cm(-1). RET decreased fluorescence life time of dye from 5 ns to 2 ns for the absorption coefficient increased from 24-202 cm(-1). These absorption coefficient dependent losses limit the optical and electrical efficiency of thin film LSC devices, and compared with bulk LSC.