A promising low cost alternative to conventional solar cells made of crystalline silicon, there is a large amount of research being dedicated throughout industry and academia towards developing OPVs and increasing their power conversion efficiency.
Recently, SWNTs were directly configured as energy conversion materials to fabricate thin-film solar cells, with nanotubes serving as both photogeneration sites and a charge carriers collecting/transport layer.
Initial tests have shown a power conversion efficiency of >1%, proving that CNTs-on-Si is a potentially suitable configuration for making solar cells.
Acid infiltration of nanotube networks significantly boosts the cell efficiency to 13.8%, as reported by Yi Jia,[5] by reducing the internal resistance that improves fill factor, and by forming photoelectrochemical units that enhance charge separation and transport.
So, plus strong acid doping, using aligned single wall carbon nanotube film can further improve power conversion efficiency (a record-high power-conversion-efficiency of >11% was achieved by Yeonwoong Jung).
[8] The dispersion of CNTs in a solution of an electron donating conjugated polymer is perhaps the most common strategy to implement CNT materials into OPVs.
PEDOT and PSS help to smooth the ITO surface, decreasing the density of pinholes and stifling current leakage that occurs along shunting paths.
To supply additional dissociation sites, other researchers have physically blended functionalized MWCNTs into P3HT polymer to create a P3HT-MWCNT with fullerene C60 double-layered device.
Weak exciton diffusion toward the donor–acceptor interface in the bilayer structure may have been the cause in addition to the fullerene C60 layer possibly experiencing poor electron transport.
Additionally, it has been found that heating to the point beyond the glass transition temperature of either P3HT or P3OT after construction can be beneficial for manipulating the phase separation of the blend.
[16] Emerging as another valuable approach for deposition, the use of tetraoctylammonium bromide in tetrahydrofuran has also been the subject of investigation to assist in suspension by exposing SWCNTs to an electrophoretic field.
[17] In fact, photoconversion efficiencies of 1.5% and 1.3% were achieved when SWCNTs were deposited in combination with light harvesting cadmium sulfide (CdS) quantum dots and porphyrins, respectively.
By dip-coating from a hydrophilic suspension, SWCNT were deposited after an initially exposing the surface to an argon plasma to achieve a power conversion efficiency of 4.9%, compared to 4% without CNTs.
The multiple chiralities of s-SWCNTs are used as the hole transport material along with the fullerene component PC71BM to fabricate heterojunctions for the PV active layer.
[24] The polychiral s-SWCNTs enable a wide range optical absorption from visible to near-infrared (NIR) light, increasing the photo current relative to using single chirality nanotubes.
In addition, the combination of costly layer deposition in vacuum and a limited supply of indium results in high quality ITO transparent electrodes being very expensive.
[31][32] Thus, possibilities exist for advancing this research to develop CNT-based transparent electrodes that exceed the performance of traditional ITO materials.
Due to the simple fabrication process, low production cost, and high efficiency, there is significant interest in dye-sensitized solar cells (DSSCs).
Thus, improving DSSC efficiency has been the subject of a variety of research investigations because it has the potential to be manufactured economically enough to compete with other solar cell technologies.
Titanium dioxide nanoparticles have been widely used as a working electrode for DSSCs because they provide a high efficiency, more than any other metal oxide semiconductor investigated.
Promoting electron transfer through film electrodes and blocking interface states lying below the edge of the conduction band are some of the non-CNT based strategies to enhance efficiency that have been employed.
To assist the electron transport to the collecting electrode surface in a DSSC, a popular concept is to utilize CNT networks as support to anchor light harvesting semiconductor particles.
Other varieties of semiconductor particles including CdSe and CdTe can induce charge-transfer processes under visible light irradiation when attached to CNTs.
The multiple chiralities of s-SWCNTs are used as the hole transport material along with the fullerene component PC71BM to fabricate heterojunctions for the PV active layer.
[24] The polychiral s-SWCNTs enable a wide range optical absorption from visible to near-infrared (NIR) light, increasing the photo current relative to using single chirality nanotubes.