A facile approach to determine the unknown refractive index (n) and extinction coefficient (k) of novel encapsulant materials used in back contact PV modules

Determining the refractive index (n) and extinction coefficient (k) of materials is of core importance in optoelectronic and photonic devices. This study demonstrates a simple yet novel method to determine n and k of unusual encapsulant materials for back contact photovoltaic (PV) modules. To avoid the problem of encapsulant browning, two non-traditional encapsulant materials, i.e., polybutadiene ionomer and thermoplastic polyolefin, are utilized as an alternative to traditionally used ethylene vinyl acetate (EVA). The n and k samples were calculated by solving the optical parameters using MATLAB code which requires transmittance and reflectance values from spectrophotometer. To validate our proposed method, glass and EVA are used as a reference. The computation of refractive index of glass and EVA has achieved an accuracy of ± 0.007 and ± 0.006, respectively. Whereas computation of extinction coefficient of glass and EVA has achieved an accuracy of ± 2.37 × 10−6 and ± 4.69 × 10−6, respectively. Thus, calculated results of n and k for glass and EVA are found in good agreement as compared to the standard values, whereas the marginal difference is within acceptable experimental error. This method can serve as a tool to find n and k of non-standard materials prior to their deployment in PV modules.