Enhanced Light Harvesting in Mesoscopic Solar Cells by Multilevel Multiscale Patterned Photoelectrodes with Superpositioned Optical Properties

Investigations on nano-and micropatterns have been intensively performed in optical applications due to their light modulation effects for enhanced photon utilization. Recently, incorporation of periodic architectures in solar cells have brought significant enhancements in light harvesting and energy conversion efficiency, however, further improvements in performance are required for practical applications due to the intrinsic limitations of single-level patterns. Herein, this study reports mesoscopic solar cells employing photoelectrodes with multilevel multiscale patterns. Polydimethylsiloxane film with multilevel nano/micropatterns (integrated in z-axis direction) is prepared by LEGO-like multiplex lithography, and its architecture is imprinted on mesoporous TiO2 electrode by soft molding technique. By various spectral analyses and simulations, advanced light harvesting properties by superposition of optical responses from constituent nano-and micropatterns are verified. The effectiveness of the strategy is confirmed by applications in dye-sensitized solar cells as a model system, wherein over 17.5% increase in efficiency (by multilevel 400 nm line/20 mu m dot structures) is observed. Also, external quantum efficiencies clearly exhibit that the improved light harvesting originates from the combined effects of diffraction grating and random scattering induced by both nano-and microarchitectures, respectively. Moreover, the validity of the multiscale approach in different dimensions is also confirmed in order to demonstrate the general advantages.