Tin Oxide (SnO_x) as Universal “Light‐Soaking” Free Electron Extraction Material for Organic Solar Cells

Abstract

In organic solar cells (OSCs), the necessity of UV activation that comes with the use of ZnO‐ and TiOx‐based electron extraction layers (EELs) can be avoided by using tin oxide (SnOx), which can be prepared at temperatures as low as 80 °C. In contrast to devices based on TiOx and ZnO, OSCs comprising SnOx as the EEL show well‐behaved solar cell characteristics with a high fill factor (FF) and high efficiency, even without the UV spectral range of the AM1.5 solar spectrum.

Simultaneous Effect of Ultraviolet Radiation and Surface Modification on the Work Function and Hole Injection Properties of ZnO Thin Films

“…Large WF shifts upon UV exposure are commonly attributed to the capture of photogenerated holes by negatively charged oxygen molecules adsorbed at the ZnO surface and at grain boundaries, followed by the desorption of the neutralized entities. [13,16,17] Storing the UV soaked sample in the dark goes along with a partial recovery of the WF, which attains a saturated value of 4.3 eV after %48 h. We noticed that the WF never regains the original value of the initial preillumination state, demonstrating the persistent effect of UV soaking. Earlier work reported persistent WF shifts upon UV light exposure of TiO 2 and ZnO if the sample is kept in vacuum or in an inert gas atmosphere.…”

“…Storing the UV soaked sample in the dark goes along with a partial recovery of the WF, which attains a saturated value of 4.3 eV after ≈48 h. We noticed that the WF never regains the original value of the initial preillumination state, demonstrating the persistent effect of UV soaking. Earlier work reported persistent WF shifts upon UV light exposure of TiO 2 and ZnO if the sample is kept in vacuum or in an inert gas atmosphere …”

“…We found that 5 min light soaking at this irradiance is sufficient to saturate the WF shift for neat and SAM‐modified ZnO (see Figure S1, Supporting Information). Large WF shifts upon UV exposure are commonly attributed to the capture of photogenerated holes by negatively charged oxygen molecules adsorbed at the ZnO surface and at grain boundaries, followed by the desorption of the neutralized entities …”

All‐Oxide MoOx/SnOx Charge Recombination Interconnects for Inverted Organic Tandem Solar Cells

“…[55] We have previously shown that the lower WF of our ALD SnO x results from Sn 2+ surface species and adsorbed water molecules, which infer downward band-bending at the SnO x surface. [17,56] The observed binding energy shift in the Sn3d peak corresponds to the variation of surface potential ϕ(d) with increasing the thickness d of the SnO x (Figure 3b, red dotted line inserted as an eye guide). As can be seen in our discussion in Figure S7 of the Supporting Information, the progression of the surface potential ϕ(d) cannot be described by simple textbook semiconductor physics in the framework of the Schottky model over the total thickness range in this study.…”

“…In single junction OSCs, we have shown that SnO x forms a universal EEL with a low-work-function, which does not rely on activation with UV light. [17] Moreover, we have demonstrated that by the use of SnO x we can avoid the occurrence of photoinduced degradation of the FF and V oc , which is commonly encountered in ZnO based devices upon prolonged exposure to solar radiation. [18] Recently, SnO x has also been considered as EEL for solar cells based on hybrid perovskites with improved efficiency and long-term stability.…”