Stabilization strategies of thin film organic luminescent solar concentrators

Thin-film organic-based luminescent solar concentrators (OLSCs) represent a promising technology to improve power conversion efficiency of photovoltaic systems (PV) inexpensively. A typical OLSC consists of a luminescent organic dye dispersed into a thin film of a transparent matrix material (typically poly(methyl-methacrylate), PMMA) deposited onto a glass plate. The luminescent species absorb the incident solar light and isotropically re-emit it red-shifted. A large part of the emitted photons is trapped in the OLSC plate by internal reflection and wave-guided towards the edges, where high efficiency solar cells are placed (see Fig.1). The emitted photon energy should match that of the band gap of the attached solar cells, to ensure high quantum yield. A major challenge for OLSC deployment is the photostability of the luminescent dye and the polymer matrix. A greater understanding of the degradation behaviour of light-exposed OLSCs is required in order to propose strategies to lengthen their life-time. Herein, we report a study on the photodegradation of a thin-film OLSC consisting of a model organic luminescent dye dispersed in a PMMA matrix, deposited onto glass substrates and exposed to UV-light in different conditions (air, controlled atmosphere). Its spectroscopic behaviour was characterized by means of FTIR, UV-vis and photoluminescence (PL) spectroscopy during irradiation time and a degradation mechanism for the dye molecule was proposed. In an attempt to improve the stability of the materials, different stabilization strategies were employed, including the use of chemical additives as well as the deposition of highly transparent protective barrier layers to prevent oxygen diffusion into the active film. The stabilization study was extended to devices comprising a thin-film OLSC coupled to mc-silicon solar cells, in order to evaluate the effect of materials degradation on device performance over time. After a systematic optimization of device parameters (dye concentration, thin-film thickness, geometric concentration factor, back-coating), the PV characteristics of the optimized system were monitored at increasing irradiation times and device stability was evaluated.