Flexible organic solar cells including efficiency enhancing grating structures

Abstract

In this work, a new method for the fabrication of organic solar cells containing functional light-trapping nanostructures on flexible substrates is presented. Polyimide is spin-coated on silicon support substrates, enabling standard micro- and nanotechnology fabrication techniques, such as photolithography and electron-beam lithography, besides the steps required for the bulk-heterojunction organic solar cell fabrication. After the production steps, the solar cells on polyimide are peeled off the silicon support substrates, resulting in flexible devices containing nanostructures for light absorption enhancement. Since the solar cells avoid using brittle electrodes, the performance of the flexible devices is not affected by the peeling process. We have investigated three different nanostructured grating designs and conclude that gratings with a 500 nm pitch distance have the highest light-trapping efficiency for the selected active layer material (P3HT:PCBM), resulting in an enhancement of about 34% on the solar cell efficiency. The presented method can be applied to a large variety of flexible nanostructured devices in future applications.

The influence of electrical effects on device performance of organic solar cells with nano-structured electrodes

“…These approaches are based on plasmonic, diffraction and scattering effects, e.g., introduced by the integration of metallic nanoparticles near or in the photoactive layer, by the inclusion of metallic and non-metallic, aperiodic or (quasi-) periodic surface structures, or by the integration of randomly distributed metallic nanoparticles in the back contact layer 15–17 . There are several reports on nanostructured inorganic solar cell efficiency improvements as a result of enhanced optical absorption, which is a dominant factor to increase the overall performance and, in this case, directly translates to an increased photocurrent 18 .…”

Nanostructures induced light harvesting enhancement in organic photovoltaics

“…By introducing a microstructured metal/dielectric interface to surmount the mismatch associated with the momentum of in-plane SPPs and incident photons, the SPP modes can be excited and the incident photons will be trapped and guided along the interface for a few micrometers until the energy is lost in metal and dielectric materials. The incident solar flux is transferred perpendicular to the incident direction and absorbed by the photoactive materials nearby the microstructured interface [105][106][107][108]. Forrest et al [108] have fabricated periodic 1-D metallic grating at the submicron scale based on nanolithography and explored their application in OPVs based on a small molecular active layer.…”

Flexible PCPDTBT:PCBM solar cells with integrated grating structures

“…Following the Ti adhesion layer (3 nm), 80 nm layer of Al was deposited, followed by deposition of 20 nm layer of Ti. As TiOx has been used as an efficient electron transport layer in solar cells [14], we have oxidized the surface of the titanium layer by oxygen plasma [10]. For the samples containing gratings on the bottom-electrodes, electron beam lithography was employed for fabrication of titanium structures.…”

“…In order to fabricate the grating nanostructures on flexible substrates, we have used polyimide spin-coated on rigid Silicon substrates, allowing for the use of standard lithography techniques for electrode and grating definition. Our previous results have shown that gratings with pitch distances of 500 and 750 nm have a potential for enhancing the efficiency in flexible P3HT:PCBM solar cells [10]. In this work, we apply diffraction gratings in solar cells made of PCPDTBT:PCBM, a material combination that has a large potential for transparent solar cell applications [11].…”

“…For diffraction gratings, efficient light absorption have been obtained in standard and inverted configuration rigid solar cells using gratings with pitch distances that vary between hundreds of nanometers up to a few micrometers [7][8][9]. We have recently reported the use of gratings as absorption enhancing structures in flexible inverted organic solar cells [10] using P3HT:PCBM as the active layer. In order to fabricate the grating nanostructures on flexible substrates, we have used polyimide spin-coated on rigid Silicon substrates, allowing for the use of standard lithography techniques for electrode and grating definition.…”