The device was made using Natcore’s liquid phase deposition (LPD) process. A cadmium/selenium (CdSe) absorber layer was grown onto a back contact substrate based on single-walled carbon nanotubes (SWNT). LPD was also used to grow a copper/selenium (CuSe) window layer onto which silver contacts were deposited. The resulting solar device shows potential for this process to make a flexible solar cell, free of high temperature semiconductor processing.
With further work the process has potential for roll-to-roll (R2R) production. The company’s R&D centre is situated near a former Kodak R2R photo film plant in Rochester, New York state.
A few years ago Natcore Technologies began attracting interest for its LPD technology in an application for improving the light absorption properties of multi-crystalline silicon cells, known as black silicon solar cells. LPD, developed at Rice University, makes it possible to grow a wide range of inorganic materials on a range of substrates using a room-temperature, environmentally friendly chemical bath.
In the flexible solar cell work nanotubes were used for a back contact embedded into the absorber layer, reducing the diffusion length to the back contact, to potentially lead to higher efficiency, because of a lower percentage of hole electron recombination.
There is potential to make the development compatible with the company’s multi-junction tandem solar cell technology to enable high efficiency extremely thin and flexible solar cells.
Other companies bringing to market high efficiency flexible thin film solar cells include Alta Devices, which has developed a process of growing very thin layers of solar cell materials on gallium arsenide (GaAs) wafers. The California-based company has been working on a GaAs solar cell technology for military and other applications, targeting the commercial unmanned aerial vehicle (UAE) market where very lightweight and efficient solar cells on the wings of craft can extend flight times without adding extra weight.