Efficiency Enhancement of Cu(In,Ga)Se₂Solar Cells Fabricated on Flexible Polyimide Substrates using Alkali-Silicate Glass Thin Layers

Abstract

Cu(In,Ga)Se 2 (CIGS) absorber layers were grown at a maximum substrate temperature of 400 C on polyimide (PI) films. The PI films were formed by spin-coating on glass substrates. Alkali doping into the CIGS layers was demonstrated using alkali-silicate glass thin layers (hereafter called ASTL) deposited on PI films prior to the sputtering of the Mo back contact layer. The quantum efficiency curves of CIGS solar cells fabricated with use of ASTL showed an enhanced absorption in the long wavelength region. Using the ASTL method, the cell efficiency of 14.7% has been demonstrated on PI substrate. #

CIGS absorbers and processes

“…The Na density in the CIGS layer can be increased by increasing the thickness of the SLGTF layer, whereas the diffusion of multi-valent metals Ca, Mg, and Al from SLGTF into the CIGS layers was found to be almost completely blocked at the Mo back contact layers and no incorporation of these elements into the CIGS layers was observed [49]. The ASTL method is a promising technique to control the doping level of Na in CIGS and enhance the performance of CIGS solar cells on a wide variety of alkalifree substrates such as ceramics, metal foils [47], and PI [48] as listed in Table II. As mentioned above, the Na density in the CIGS layer can be controlled by variation in the thickness of the SLGTF deposited on the substrate. Figures 13(a) and (b) show secondary ion mass spectroscopy (SIMS) profiles of Figure 11.…”

“…The PI substrate used was prepared on glass substrates by spin-coating and is peeled off after device fabrication. This PI substrate offers the advantage of fabrication of flexible CIGS solar cells using a common production-line designed for rigid CIGS panel module fabrication [48].…”

Sodium diffusion in boroaluminosilicate glasses

“…Understanding the fundamentals of alkali diffusion in BAS glasses is crucial for recent high-tech applications of BAS glasses such as high strength ion exchanged glass [5,6] and substrate glass for solar energy conversion [7,8]. Chemical strengthening of glass occurs by an ion exchange process of large alkali ions (e.g., K + ) from a molten salt bath with smaller alkali ions (e.g., Na + ) in the host glass.…”

Applications of Oxide Coatings in Photovoltaic Devices

“…Al 2 O 3 coated on polymer substrates has been used to protect the subsequently grown CIGS device from ingress of moisture [91]. On the other hand, thin film alkali-silicate glass layers were grown on polymer films to supply sodium to the CIGS absorber [92].…”