Shell-shaped active layers for omnidirectional organic photovoltaic cells

Abstract

.For the employment of organic photovoltaic cells in wearable electronic systems, improvements in energy conversion efficiency and omnidirectionality (angular coverage) are highly appreciated. This study aims at those improvements by introducing shell-shaped active layers. The proposed device structures enhance light absorption and angular range through light coupling to guided modes in the active layer. Two shapes, i.e., a triangle and a semicircle, are examined for the shell cross-sections. Numerical simulation using finite-element analysis and finite-difference time-domain methods demonstrates that the devices with the triangular-shell-shaped active layers exhibit an average absorption enhancement of up to 63% for transverse electric (TE)-polarization and up to 32% for transverse magnetic (TM)-polarization when compared with the flat active layers of the same thicknesses. The average enhancements of the semicircular-shell-shaped active layers are found to be slightly lower than those values, with 60% for TE and 28% for TM. The examined structures also show good omnidirectionality with decent absorption up to an 81 deg incidence angle for the triangular-shell-shaped device and up to a 76 deg angle for the semicircular one when TM polarization is considered. These absorption enhancements and improved angular coverages make the proposed structures highly attractive for wearable electronic system applications.

Hemispherical-shell-shaped organic photovoltaic cells for absorption enhancement and improved angular coverage

“…Another figure of merit, EFave, the average enhancement factor, was calculated as a ratio of IAave between the proposed device and a flat device. The third figure of merit, θcov, a measure of an angular coverage (omnidirectionality), was defined differently from the previous report 24 as the incidence angle where IA becomes 90% of IAave,0−45. IAave,0−45 is defined as the average value of IA between 0 deg and 45 deg of incidence angles where the IA curves are relatively flat.…”

“…In our previous reports, we also introduced new solar cell structures based on shell-shaped organic active layers. 23,24 These shell-shaped structures were proposed with the aim of keeping the fabrication processes as simple as possible. In addition, because the proposed structures are made of continuous layers, they can be more robust than the ones that utilize localized components.…”

“…obtained a similar effect by wrapping organic solar cells around a fiber array. In our previous reports, we also introduced new solar cell structures based on shell-shaped organic active layers 23 , 24 . These shell-shaped structures were proposed with the aim of keeping the fabrication processes as simple as possible.…”

“…In addition, because the proposed structures are made of continuous layers, they can be more robust than the ones that utilize localized components. In those previous studies, we examined cylindrical shells with a cross-section of a semicircle 23 or that of a triangle 24 via numerical analysis. It was learned that compared to the regular flat structures, the proposed cylindrical-shell-shaped structures could result in enhanced light absorption and broadened angular coverage, mainly due to light coupling to guided modes within the active layer, producing the effect of light retention.…”