New MAterials for Tandem Solar cells (MATS) (avsluttet)

• Bergsbak, Ingvild; Nordseth, Ørnulf; Saxegaard, Kjetil Karlsen; Olsen, Vegard Skiftestad; Wenckstern, Holger Von & Bergum, Kristin (2024). Device Simulation of 25.9% Efficient ZnOxNy/Si Tandem Solar Cell. Advanced Theory and Simulations. 7(12). doi: 10.1002/adts.202400252. Fulltekst i vitenarkiv Vis sammendrag

  The novel, high electron mobility material ZnOxNy has been investigated theoretically as an absorber in a two-terminal tandem solar cell. In addition to its high mobility, ZnOxNy can attain sufficiently low carrier concentration to enable pn-junctions, and has a tunable bandgap around the 1.7 eV range. It is therefore suitable for pairing with a Si-based bottom cell. In addition to the ZnOxNy layer, the tandem cell consists of a Cu2O emitter and a Si heterojunction bottom cell. A buffer layer is introduced between the emitter and absorber in the top cell to mediate a large valence band offset that resulted in a poor fill factor, FF. A ZnOxNy buffer layer bandgap of 1.5 eV gave the highest power conversion efficiency (PCE). The objective is to estimate the optimal performance of ZnOxNy in a tandem solar cell. The dependence of current–voltage (J–V) characteristics on thickness, mobility and carrier concentration in the ZnOxNy layer is evaluated, and found to yield maximum performance with 0.35 𝛍m, 250 cm2 Vs–1 and 1016 cm−3, respectively. Using these conditions, the J–V parameters of the device under AM1.5 illumination are short circuit current density, JSC = 17.76 mA cm−2, open circuit voltage, VOC = 1.74 V, FF = 83.8% and PCE = 25.9%. With this, it is reported on, to the best of the knowledge, the first device simulation based on ZnOxNy.

• Saxegaard, Kjetil Karlsen; Monakhov, Eduard; Vines, Lasse & Bergum, Kristin (2023). Characteristics of ZnON films and heterojunction diodes with varying O:N ratios. Thin Solid Films. ISSN 0040-6090. 782. doi: 10.1016/j.tsf.2023.139968. Fulltekst i vitenarkiv Vis sammendrag

  Zinc Oxynitride (ZnOxNy) thin films display high mobilities and a considerable tunability of both the free electron concentration and optical band gap. The properties achievable for this material system makes ZnOxNy an intriguing n-type absorber candidate in silicon-based tandem solar cells. We have studied how the O:N ratio affect structural, optical and electrical properties of magnetron sputtered ZnOxNy thin films, as well the electrical behavior of ZnOxNy-Si pn heterojunction diodes. X-ray diffraction of the ZnOxNy films indicate either a Zn3N2-like structure or ZnO-like grains in combination with structural disorder. As the O:N ratio is increased, the optical band gap of ZnOxNy films increase from 1.1 to 1.9 eV. Hall effect measurements of the n-type ZnOxNy films show free electron concentrations varying with the O:N ratio, from 9.8 × 1017 to 1.5 × 1016 cm−3. Hall mobility up to 88 cm2∕Vs is achieved. We observe the formation of pn heterojunction diodes between ZnOxNy-films and p-Si. The electrical characteristics of these diodes are shown to depend on the ZnOxNy anion composition. Current rectification of 3.7 orders of magnitude is achieved between -1 and 1 V at room temperature. However, the built in voltage extracted from capacitance–voltage measurements are higher than theory suggest, implying an influence of defects on the electrical characteristics.

• Nyborg, Martin; Azarov, Alexander; Bergum, Kristin & Monakhov, Eduard (2021). Deposition and characterization of lithium doped direct current magnetron sputtered Cu2O films. Thin Solid Films. ISSN 0040-6090. 722(31), s. 1–5. doi: 10.1016/j.tsf.2021.138573. Fulltekst i vitenarkiv
• Nyborg, Martin; Karlsen, Kjetil; Bergum, Kristin & Monakhov, Eduard (2021). Dominant acceptors in Li doped, magnetron deposited Cu2O films. Materials Research Express. 8(12), s. 1–8. doi: 10.1088/2053-1591/ac3e24. Fulltekst i vitenarkiv Vis sammendrag

  Cu 2 O films deposited by reactive magnetron sputtering with varying Li concentrations have been investigated by a combination of temperature-dependent Hall effect measurement and thermal admittance spectroscopy. As measured by secondary ion mass spectrometry, Li concentrations up to 5 × 10 20 Li/cm 3 have been achieved. Li doping significantly alters the electrical properties of Cu 2 O and increases hole concentration at room temperature for higher Li concentrations. Moreover, the apparent activation energy for the dominant acceptors decreases from around 0.2 eV for undoped or lightly doped Cu 2 O down to as low as 0.05 eV for higher Li concentrations.

• Olsen, Vegard Skiftestad; Øversjøen, Vetle; Gogova-Petrova, Daniela; Pecz, Bela; Galeckas, Augustinas & Borgersen, Jon Arthur [Vis alle 9 forfattere av denne artikkelen] (2021). ZnSnN2 in Real Space and k-Space: Lattice Constants, Dislocation Density, and Optical Band Gap. Advanced Optical Materials. doi: 10.1002/adom.202100015. Fulltekst i vitenarkiv
• Kumar, Raj; Bergum, Kristin; Riise, Heine Nygard; Monakhov, Eduard; Galeckas, Augustinas & Svensson, Bengt Gunnar (2020). Impact of post annealing and hydrogen implantation on functional properties of Cu2O thin films for photovoltaic applications. Journal of Alloys and Compounds. ISSN 0925-8388. 825(5), s. 1–8. doi: 10.1016/j.jallcom.2020.153982. Fulltekst i vitenarkiv Vis sammendrag

  Polycrystalline cuprous oxide (Cu2O) thin films were sputtered, annealed (900 °C rapid thermal annealing) and subsequently implanted with various hydrogen ion (H+) doses from 5E13 to 2E15 cm−2 with a low acceleration energy of 36 keV at room temperature to tailor the functional properties of the thin films for solar cell application. The annealed and H+ implanted Cu2O thin films were post annealed at low temperatures from 100 °C to 600 °C in an inert atmosphere to promote hydrogen passivation of prevalent intrinsic acceptors and tune the carrier concentration for optimum performance as an absorption layer in a heterojunction solar cell. The H+ incorporation and post annealing tuned the structural, optical and electrical properties of annealed polycrystalline Cu2O thin films. The results show an enhancement of the excitonic feature around ∼2.0 eV with H+ dose. The normalized photoluminescence (PL) area around ∼1.7 eV was drastically enhanced with increasing H+ doses compared to excitonic and copper vacancy related area. The normalized total PL quantum efficiency shows an enhancement in yield with elevated H+ doses by two orders of magnitude. The hole concentration decreases down to ∼1013 cm−3, while hole mobility and resistivity increase to ∼27 cm2/V and ∼2.4 kΩcm, respectively, as the H+ implantation goes from lower to higher doses. In addition, the post annealing and H+ incorporation lead to a change in the energy level of the major acceptor from 0.21 eV to 0.27 eV above the valence band maximum. By following the qualitative (PL analysis) and quantitative (Hall data) outcomes, we can conclude that H+ implantation and post annealing likely indicates the passivation of both acceptor defects and compensating donor defects.

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• Saxegaard, Kjetil Karlsen; Bergum, Kristin; Monakhov, Eduard & Vines, Lasse (2022). The effect of oxygen and nitrogen concentrations on Opto-electronic properties of ZnON films. Fulltekst i vitenarkiv
• Karlsen, Kjetil; Bergum, Kristin; Monakhov, Eduard & Vines, Lasse (2022). The effect of oxygen and nitrogen concentrations on Opto-electronic properties of ZnON films. Fulltekst i vitenarkiv
• Karlsen, Kjetil; Bergum, Kristin; Monakhov, Eduard & Vines, Lasse (2022). The effect of oxygen and nitrogen concentrations on Opto-electronic properties of ZnOxNy films. Fulltekst i vitenarkiv
• Karlsen, Kjetil; Bergum, Kristin; Monakhov, Eduard & Vines, Lasse (2022). Electronic properties and dominant levels in ZnON. Fulltekst i vitenarkiv
• Karlsen, Kjetil; Bergum, Kristin; Monakhov, Eduard & Vines, Lasse (2022). The effect of oxygen and nitrogen concentrations on Opto-electronic properties of ZnON films. Fulltekst i vitenarkiv
• Bergum, Kristin; Selj, Josefine Helene Krogh & Melteig, Elina (2022). Glemmer Norge sola når vi snakker om fornybar energi? [Internet]. Universitetsplassen podcast for UiO, ep 85. Fulltekst i vitenarkiv
• Bergum, Kristin; Monakhov, Eduard & Vines, Lasse (2022). The effect of oxygen and nitrogen concentrations on ZnON films. Fulltekst i vitenarkiv
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