Low-Temperature High-Mobility Amorphous IZO for Silicon Heterojunction Solar Cells

Transparent Electrodes for Efficient Optoelectronics

“…[23] For example, the optical band gap (E g ) of sputtered ITO, IZO and IO:H films are between 3.5 and 3.8 eV. [111] Transparent electrodes with low absorptance in the NIR-IR part of the spectrum (transparent electrodes with low FCA) are required for CIGS, SHJ and multi-junction devices, such as perovskite-onsilicon [109,112] and perovskite-on-CIGS [113] tandem solar cells, as these devices employ optical absorbers that are active in this range of the spectrum. These tandem approaches are new highefficiency photovoltaic technologies, with a potential to reach about 30% efficiency, [114,115] clearly underscoring the critical importance and urgency of designing transparent electrodes with exceptionally large broadband transparency.…”

“…Even with an amorphous structure (different from polycrystalline IO:H and ICO:H), IZO can have electron mobilities up to 60 cm 2 V −1 s −1 for free carrier densities between 1-3 × 10 20 cm −3 . [111,125,126] An attractive feature of these TCOs is that they already have excellent optoelectronic properties in their as-deposited state; these properties are not much affected by post-deposition annealing and offer opportunities for temperature-sensitive applications. A possible drawback is their relatively high absorption in the UV-vis range due to optical band gap narrowing.…”

“…A possible drawback is their relatively high absorption in the UV-vis range due to optical band gap narrowing. [111] This is a common effect in amorphous materials caused by exponential subgap tails due to disorder (also called Urbach tails) [127,128] and the presence of defects that introduce subgap absorption centers. [129] The application of IZO in solar cells has been demonstrated in SHJ [111] and perovskite solar cells.…”

“…[111] This is a common effect in amorphous materials caused by exponential subgap tails due to disorder (also called Urbach tails) [127,128] and the presence of defects that introduce subgap absorption centers. [129] The application of IZO in solar cells has been demonstrated in SHJ [111] and perovskite solar cells. [130] A particularly attractive feature of all indium-oxide-based electrodes (including ITO) is the fact that their refractive index is close to 2.…”

“…Such TCOs have demonstrated their value in SHJ and perovskite solar cell fabrication. [111,130] As mentioned earlier, gentle deposition on underlying layers can also be a critical factor in electrode choice and raises questions about the use of well-established physical vapor deposition (PVD) techniques, such as sputtering or pulsed laser deposition for certain applications. Sputter damage, caused by UV radiation and particle bombardment, is a known phenomenon in organic, [16] SHJ, [15] and perovskite [169] solar cells as well as flexible displays.…”