Study of Complex Optical Constants of Neat Cadmium Selenide Nanoplatelets Thin Films by Spectroscopic Ellipsometry

Knowledge of tunability of complex optical constants of colloidal CdSe nanoplatelets (NPLs) thin films is essential for accurate modeling and design of NPL-containing optoelectronic devices. Here, dielectric functions, complex optical conductivities, and absorption coefficients of a series of CdSe NPL films with a varying number of atomic layers were investigated in a combination of spectroscopic ellipsometry techniques and transmittance measurements over a broad spectral range. Fine electronic structures were deciphered from the dielectric functions. Oscillator strengths at the lowest exciton resonance up to 0.62 for a series of CdSe NPL films were also determined. From our results, increasing the number of monolayers was found to boost the complex optical constants and the amplitude of the coupling strength of the fundamental exciton state mainly due to higher inorganic volume filling factors and pronounced surface passivation. Our work gives insights into both the interpretation and improvements of performance of CdSe NPL-based photoelectronic applications.