Lichttechnisches Institut, Fakultät für Elektrotechnik und Informationstechnik, KIT

32. Međunarodni kongres o procesnoj industriji, Beograd, 30-31. maj 2019 32nd International Congress on Process Industry, Belgrade, May 30-31, 2019

Perovskite-Silicon Tandem Solar Cells

Lovro Marković, University of Zagreb

Table of Content

Solar Cells in General

Perovskites

About Tandems

Architectures

Materials Optimization

Fabrication / Modules

Perovskites braking records

https://www.photon.info/en/news/oxford-pv-achieved-273-percent-conversion-efficiency-perovskite-solar-cell

Promises of perovskite materials

Absorption and diffusion

Bandgap and high voltage

Solution processable

Lightweight

Paetzold U. Perovskites Photovoltaics - Lecture slides. Lichttechnisches Institut, KIT.

Promises of perovskite materials

https://www.solarpowerworldonline.com/2015/04/the-perfect-marriage-silicon-and-perovskite-solar-cells/

Why tandems?

Peters M et al. Spectrally-Selective Photonic Structures for PV Applications. Energies. 2010; 3(2): 171-193Liu Z. Optical loss analysis of silicon wafer based solar cells and modules. 10.13140/RG.2.2.26172.74881.

Thermalisation losses

Sub-bandgap losses

Why tandems?

https://www.quora.com/What-are-the-physical-limitations-were-hitting-in-solar-PV-efficiency-and-where-might-we-see-breakthroughs; De Vos, A. Detailed balance limit of the efficiency of tandem solar cells. Journal of Physics D: Applied Physics. 1980; 13 (5): 839-846

Surpassing Shockley–Queisser limit

Why perovskite / Si tandems?

Suitable bandgap span (1.5 – > 2.2 eV)

High transparency (<Eg) – small Urbach tail – sharp abs. edges

Solution processable (low-cost)

Si – the most mature and developed PV technology

Albrecht S, Rech B. On top of commercial photovoltaics. Nat. Energy. 2017; 2: 16196

Different architectures

two-terminal monolithic mechanically stacked four-terminal

Bush, K A et Al. 23.6%-efficient monolithic perovskite/silicon tandem solar cells with improved stability. Nat. Energy. 2017; 2 : 17009

2T structure

Tunnel junction in between

Higher possible efficiencies (less additional circuits, reduced parasitic absorption)

„Current-matching”

Grant, D T et Al. Design guidelines for perovskite/silicon 2-terminal tandem solar cells: an optical study. Opt. Express. 2016; 24: A1454-A1470

4T structure

Both sub-cells independently optimized

Independent of seasonal and angular variations in solar spectrum

Additional circuitry

Jaysankar M et Al. Four-Terminal Perovskite/Silicon Multijunction Solar Modules. Adv. Energy Mater. 2017; 7: 1602807

First Perovskite / Si tandem

Produced in 2015!

Achieved 13.7%

Problems with „current-matching”

Bandgap optimization in 2T

Tunable by changing halide concentrations

Should be in range 1.7-1.8 eV

Covering the majority of solar spectrum

„Current – matching” – higher voltage – lower current

Stability problems of possible materials

Top-cell materials

Cs0.17FA0.83Pb(Br0.17I0.83)3

Addition of Cs to improve photo- and thermal- stabilityMaintaining the high-efficiency level

Top-cell materials

Addition of Rb (smaller than Cs)

Improving efficiency and hysteresis of the top-cell

Better transparency (84%, in range 720–1100 nm)

4T world record!!!

Or?

https://www.photon.info/en/news/oxford-pv-achieved-273-percent-conversion-efficiency-perovskite-solar-cell

Bottom-cell materials

Silicon heterojunction (SHJ)

Highest efficiency silicon technology

Optimal light-management

Parasitic absorption

Achieving sub-bandgap transparency of top cell (sharp absorption edges)

Lack of appropriate ARC and textured surface on the bottom cell

Bottom Si cell ( ≈ 10% PQE)

Duong, T et Al. Rubidium multication perovskite with optimized bandgap for perovskite silicon tandem with over ‐26% efficiency. Adv. Energy Mater. 2017; 1700228.

Optimal light-management

Developing new materials with higher transmission (ZnO, TiO2, SnO2)

Optimization of layer thinknesses (e.g. tunnel junction layer)

Light – trapping techniques

2 T > 4 T due to non-existance of air-ITO interface (less reflection on surface of Si-cell)

Optimal light-management

2T world record!!!

11.06.18

Texturing of all surfaces

Rear reflector and texturing (IR backscattering)

Sahli, F et Al. Fully textured monolithic perovskite/silicon tandem solar cells with 25.2% power conversion efficiency. Nat. Materials. 2018

Fabrication

Spin coating

Problems with fabricating functional layers on Si-cell as substrateAfter texturing – vapor deposition has to be usedTemperature problems – TiO2 mesoporous layer (400 °C) – degradation of a:Si surface passivated layers of bottom cell

Wu Y et Al. Monolithic perovskite/silicon-homojunction tandem solar cell. Energy Environ. 2017; Sci. 10: 2472

Fabrication

Sputtering of ITO electrodes can damage perovskite

Addition of low-work-function metal-oxides

ZnO, TiO2, SnO2

Increases thermal and environmental (encapsulation) stability

Bush, K A et Al. 23.6%-efficient monolithic perovskite/silicon tandem solar cells with improved stability. Nat. Energy. 2017; 2 : 17009

Going to modules

4T cells mechanically stacked

Problematic size of individual perovskite solar cell ( < 1 cm2 )

Trade-off between sheet resistance of electrode and transparent electrodes thickness

Jaysankar M et Al. Four-Terminal Perovskite/Silicon Multijunction Solar Modules. Adv. Energy Mater. 2017; 7: 1602807

Going to modules

Cell-on-cell or module-on-module architectures

Jaysankar M et Al. Four-Terminal Perovskite/Silicon Multijunction Solar Modules. Adv. Energy Mater. 2017; 7: 1602807

Going to modules

Perovskite solar cells generally produced on flat glass surface (high-reflection)

Need for patterning surfaces of both cells

AR – pyramids attached to the glass surface

Refractive index matching layer (IML) between stacked cells

Jaysankar M et Al. Perovskite-silicon tandem solar modules with optimised light harvesting. Energy Environ. Sci. 2018.

Going to modules

Jaysankar M et Al. Perovskite-silicon tandem solar modules with optimised light harvesting. Energy Environ. Sci. 2018.

Conclusion

Perovskite / Si tandems as one of the most probable candidates for solar cells of future

Rapidly growing research field

Optimized modules in the beginning of research

Comercial production still far away

Thank you for your attention!

Questions?