The impact of quantum dot concentration on the optical properties of QD/PMMA luminescent down-shifting films applied to CdTe photovoltaic devices

Semiconductor quantum dots (QDs) have been encapsulated in poly(methyl, methacrylate) (PMMA) to prepare luminescent down-shifting films. The concentration of the QDs within each film has been varied, up to a maximum of 240 µg/mm3 and the optical properties have been characterised in detail. The QD/PMMA films have been placed over thin-film CdS/CdTe photovoltaic devices and improvements to cell performance have been recorded via external quantum efficiency and current–voltage measurements. The best overall improvement to performance, compared to the uncoated device, was 1.7%. This was obtained with a QD density of 48 µg/mm3, while the largest improvement to short-wavelength photocurrent was 30.30%, with a QD density of 192 µg/mm3. To further explain these results laser beam induced current measurements were carried out using laser wavelengths of 405 and 658 nm on individual cells with and without QD/PMMA films attached.