Engineering Schottky Contacts in Open-Air Fabricated Heterojunction Solar Cells to Enable High Performance and Ohmic Charge Transport

Abstract

The efficiencies of open-air processed Cu2O/Zn1–xMgxO heterojunction solar cells are doubled by reducing the effect of the Schottky barrier between Zn1–xMgxO and the indium tin oxide (ITO) top contact. By depositing Zn1–xMgxO with a long band-tail, charge flows through the Zn1–xMgxO/ITO Schottky barrier without rectification by hopping between the sub-bandgap states. High current densities are obtained by controlling the Zn1–xMgxO thickness to ensure that the Schottky barrier is spatially removed from the p–n junction, allowing the full built-in potential to form, in addition to taking advantage of the increased electrical conductivity of the Zn1–xMgxO films with increasing thickness. This work therefore shows that the Zn1–xMgxO window layer sub-bandgap state density and thickness are critical parameters that can be engineered to minimize the effect of Schottky barriers on device performance. More generally, these findings show how to improve the performance of other photovoltaic system reliant on transparent top contacts, e.g., CZTS and CIGS.

Strongly Enhanced Photovoltaic Performance and Defect Physics of Air‐Stable Bismuth Oxyiodide (BiOI)

“…Cu 2 ZnSnS 4 has a similar Urbach energy and has a V OC 0.5 V below its Shockley-Queisser limit value. [46,50] Band tails and sub-bandgap states present in the NiO x ( Figure S43, Supporting Information) and ZnO layers (measured previously, [45,51] and from Figure S42, Supporting Information) can also lead to V OC losses due to carrier thermalization or recombination from the band tails. [45,52] Further device modeling and temperature-dependent V OC measurements are required to quantify the magnitudes of these different effects.…”

Research Update: Atmospheric pressure spatial atomic layer deposition of ZnO thin films: Reactors, doping, and devices

“…23,34,37,38 AP-SALD ZnO was first reported by Levy et al 16 Their reactor was further developed by Cambridge University and used to produce Cu 2 O, 35 TiO 2 , 24 and doped and intrinsic ZnO. 18,23,25,26,28,36,39 Various names have been given to describe this system, but in this research update, we standardize its name to the Cambridge University Close Proximity (CUCP) reactor (design details are given in Ref. 24).…”

“…11,18,19,25,28,39,50 A particularly effective way of tuning the ZnO conduction band position is through Mg incorporation. 51 This has been achieved by AP-SALD using bis(ethylcyclopentadienyl)magnesium (Mg(CpEt) 2 ) as the magnesium precursor.…”

“…28 Reducing this conduction band offset through Mg incorporation into the ZnO layer, therefore, reduces interfacial recombination, giving high V OC values and efficiencies. 28 Further improvements, however, will depend on avoiding forming the more stable CuO phase on Cu 2 O when it is heated atmospherically during the deposition of AP-SALD Zn 1−x Mg x O on top. 7 Zn 1−x Mg x O has also been studied in LEDs (see Ref.…”

“…We also seek to standardize the terminology used. For example, the various terms previously employed to describe these reactors are atmospheric atomic layer deposition (AALD), [23][24][25][26] spatial atmospheric atomic layer deposition (SAALD), 5,27,28 and atmospheric spatial atomic layer deposition. 29 Here, the term is standardized to AP-SALD.…”