Thin film small molecule organic photovoltaic solar cell
A thin film organic photovoltaic device or solar cell in one embodiment includes an organic active bilayer and an ultrathin two-dimensional metallic nanogrid as a transparent conducting electrode which receives incident light. The nanogrid excites surface plasmonic resonances at an interface between the nanogrid and active bilayer from the incident light to enhance photon absorption in the active bilayer below the nanogrid. In another embodiment, spatially separated nanograting electrodes may alternatively be formed by double one-dimensional nanogratings disposed on opposite sides of the organic active bilayer. The spatially separated nanogratings may be oriented perpendicular to each other.
1. A thin film organic photovoltaic solar cell comprising:
a bottom electrode layer;
an electron transport layer disposed thereon and including a one-dimensional metallic bottom nanograting embedded therein;
an organic active bilayer disposed thereon comprising an acceptor layer and a donor layer, the acceptor and donor layers being formed of electrically conductive organic polymers selected to form a heterojunction at an interface between the acceptor and donor layers; and
a transparent top conducting electrode layer disposed thereon, the top electrode layer comprising a transparent conductive material and a one-dimensional metallic top nanograting embedded therein;
wherein the nanogratings have thicknesses selected to excite surface plasmonic resonances of all light polarizations at an interface between the nanogratings and active bilayer from incident light on the transparent conducting electrode layer for increasing photon absorption in the active bilayer; and
wherein the top nanograting is arranged in a different orientation than the bottom nanograting forming a composite nanograting structure possessing two-dimensional symmetry in top plane view having polarization-independent optical absorption.
2. The solar cell of claim 1 wherein the top nanograting is oriented perpendicular to the bottom nanograting.
3. The solar cell of claim 1 , wherein the acceptor layer of the active layer is 3,4,9,10-perylenetetracarboxylic bis-benzimidazole and the donor layer is copper pthalocyanine, and wherein the total photon absorptivity of the active bilayer is at least 0.595 in a wavelength region between 400 nm and 800 nm.
4. The solar cell of claim 1 , wherein the top nanograting has a thickness less than 50 nm.
5. The solar cell of claim 1 , wherein the top nanograting has a linewidth in a range from and including 60 nm to 80 nm.
6. The solar cell of claim 5 , wherein the bottom nanograting has a thickness in the range from and including 50 nm to 70 nm.
7. The solar cell of claim 1 , wherein the bottom nanograting and the top nanograting have the same thickness.
8. The solar cell of claim 1 , wherein linear elements of the top and bottom nanogratings are spaced apart at a same period.
9. The solar cell of claim 1 , wherein the total photon absorption of the solar cell is maximized when:
the top nanograting has a thickness of 15 nm and a linewidth 70 nm; and
the bottom nanograting has a thickness of 60 nm and a linewidth of 70 nm.
10. A thin film organic photovoltaic device comprising:
a bottom electrode layer;
an electron transport layer disposed thereon and including a one-dimensional metallic bottom nanograting embedded therein, the bottom nanograting formed of a first array of parallel first linear elements;
an organic active bilayer disposed thereon comprising an acceptor layer and a donor layer, the acceptor and donor layers being formed of electrically conductive organic polymers selected to form a heterojunction at an interface between the acceptor and donor layers; and
a transparent top conducting electrode layer disposed thereon, the top electrode layer comprising a transparent conductive material and a one-dimensional metallic top nanograting embedded therein, the top nanograting formed of a second array of parallel second linear elements oriented perpendicular to the first linear elements of the first array forming a composite nanograting structure with two-dimensional symmetry in top plane view having polarization-independent optical absorption;
wherein the nanogratings have thicknesses selected to excite surface plasmonic resonances of all light polarizations at an interface between the nanogratings and active bilayer from incident light on the transparent conducting electrode layer for increasing photon absorption in the active bilayer.