Flexible and Semi‐Transparent Ultra‐Thin CIGSe Solar Cells Prepared on Ultra‐Thin Glass Substrate: A Key to Flexible Bifacial Photovoltaic Applications

Abstract

For applications to semi‐transparent and/or bifacial solar cells in building‐integrated photovoltaics and building‐applied photovoltaics, studies are underway to reduce the processing cost and time by decreasing the thickness of Cu(In1−x,Gax)Se2 (CIGSe) absorber to the ultra‐thin scale (≤500 nm). To dynamically and affordably meet the growing demand for electric power, daylighting, and architectural aesthetics of buildings in urban area, flexible semi‐transparent ultra‐thin (F‐STUT) CIGSe solar cells are proposed on flexible ultra‐thin glass (UTG) and compared with rigid semi‐transparent ultra‐thin (STUT) CIGSe solar cells fabricated on soda‐lime glass (SLG). At all the tested deposition temperatures of CIGSe, the F‐STUT CIGSe solar cells exhibit superior performance compared to the rigid STUT CIGSe solar cells. Furthermore, through realistic measurement under ≈1.3‐sun illumination, maximum bifacial power conversion efficiency of 11.90% and 13.23% are obtained for SLG and UTG, respectively. The major advantages of using UTG instead of SLG are not only the intrinsic characteristics of UTG, such as flexibility and high transmittance, but also collateral benefits such as the larger CIGSe grain size at the deposition temperature, better CIGSe crystalline quality, more precise controllability of the alkali element, and reduced thickness of the interfacial GaOx layer, which enhance the photovoltaic parameters.

High‐Performance and Industrially Viable Nanostructured SiOx Layers for Interface Passivation in Thin Film Solar Cells

“…The CIGS thickness reduction from the standard 2 μm to the ultrathin range will allow for a reduction in production costs by increasing machine throughput. [ 7,8 ] Moreover, the thickness reduction is in line with the recommendations from a recently conducted CIGS PV installations life cycle assessment study that encourages a continuous reduction on the rare metals usage, [ 9 ] thus allowing for lower production costs and also lower environmental impact. From a device performance point of view, keeping the conventional architecture with an ultrathin CIGS layer raises new optoelectronic concerns.…”

Flexible electrochromic devices prepared on ultra-thin ITO glass

“…24,25 As an alternative to soft polymer-based substrates ultra-thin glass has been gained attention in recent years for various applications such as organic light emitting diodes (OLEDs), 26 electrowetting devices, 27 smart windows, 28,29 and solar cells. 30,31 A few studies of ITO-coated ultra-thin and flexible glass for the aforementioned applications have been conducted. Castro-Hermosa et al developed flexible perovskite solar cells on ultra-thin ITO glass via roll-to-roll sputtering processes for indoor power generators.…”

“…31 Kim et al investigated flexible and semi-transparent Cu(In 1Àx ,Ga x )Se 2 (CIGSe) solar cells prepared on ultra-thin glass for their use in bifacial photovoltaics. 30 In comparison to commercially available ITO glass or PET-based transparent conductive substrates, ultra-thin ITO glass provides good optical properties with an average visible light transmittance (t v ) of 81.2%, while possessing a sheet resistance of 13 O sq À1 and 1600 bending cycles at 20.5 mm curvature. 30 Fahland et al…”

“…30 In comparison to commercially available ITO glass or PET-based transparent conductive substrates, ultra-thin ITO glass provides good optical properties with an average visible light transmittance (t v ) of 81.2%, while possessing a sheet resistance of 13 O sq À1 and 1600 bending cycles at 20.5 mm curvature. 30 Fahland et al…”

Is a passivated back contact always beneficial for Cu (In,Ga)Se2 solar cells?

“…For instance, TCO substrates favor the realization of pronounced light trapping in ultrathin CIGSe solar cells. [23][24][25][26][27] Furthermore, CIGSe solar cells on TCOs can be utilized in tandem cells as a top cell, 28 bifacial solar cells, 29,30 in solar window, and in backwall configuration. 31,32 It should be noted that, due to the high temperature during CIGSe absorber deposition, TCOs may be thermally instable 19,20 and ITO (Sn:…”