This document discusses the processes of up-conversion (UC) and down-conversion (DC) in solar cells to enhance efficiency and reduce energy loss. It explains the working mechanisms of both processes, materials used, and their significance in improving solar cell performance. The document also highlights the potential efficiency improvements achievable through these technologies.

1. Up-Conversion and Down-
Conversion in Solar Cells
AJIT MEENA
V21113
MSc physics
Special thanks
Project instructor
Dr. Ranbir Singh
PH-614 SEMINAR AND REPORT
INDIAN INSTITUTE OF TECHNOLOGY, MANDI HIMACHAL( 175005)

2. Content
1. Introduction
1.1 solar cells
1.2 Up-conversion( UC) and Down-conversion ( DC )
2. Up- conversion (UC) in solar cells
2.1 working mechanism
3. Down-conversion (DC) in solar cells
3.1 working mechanism
4. Solar spectral conversion in solar cell
5. Material choice for UC and DC
6. Efficiency improvement using UC and DC in solar cells
7. Other importance of UC and DC in solar cell

3. 1. Introduction
Solar cell- Electronic device that converts the light energy directly into electricity by photovoltaic
effect.
 Cost and efficiency are related in solar cell
like: Cost/Watt
 Si –single junction solar cell- costly
Why up conversion and down
conversion in solar cell ?
1. Reducing thermalization loss via down conversion.
2. Decreasing transmission loss ( up conversion )
Fig. 1 Solar spectrum with energy losses in solar
cell
Watt Cost
[solar spectrum conversion for photovoltaics using
nanoparticles { fig .3}]

4. 1.2.1 Up conversion ( UC )
Up conversion is a process in photovoltaic cells that converts low
energy ( high wavelength ) photons into high energy (lower wavelength) photons.
Infrared light Visible light
1.2.2 Down-conversion ( DC )
Down conversion is a process where high energy photons are
converted into low energy photons.
UC
 Spectral Conversion Process Helps to Improve Efficiency of the Solar Cells
Ultraviolet (UV) Visible light

5. 2. Up-conversion in solar cell
For modification of spectral mismatch, the up converter are uses back to the solar cell ( bifacial solar cell ).
 Photon with low energy than band gap of solar cells
and transmitted by solar cell are directed to the back.
 Up converter – Absorbs the transmitted light and
emits a light with high energy photon .
• Sensitizer
• Activator
• Back reflector
Fig 2. Design of solar cell with Up converter
Main components of Up converter
Bifacial solar cell
Up converter layer
Back reflector
Solar spectrum

6. 2.1 Working principle of Up conversion in solar cell
Fig. 3 Working process with up converter
 Low energy photons –transmitted
by solar cell and absorbs by
sensitizer.
 low energy photon excite the
energy state of activator through
non radiative relaxation.
 Radiative emission ( excite state –
ground state )by activator as a high
energy photon Open AccessRev
[ Enhancing Solar Cell Efficiency Using Photon Up-conversion Materials fig. 7 ]

7. Fig.4 energy level or energy state of up converter
( lanthanide ions ) [1]
 Energy level representation of up convertor materials( lanthanide ions )--
4F7/2 - EXCITED STATE ( Er3+ )
2F5/2 - EXCITED STATE ( Yb3+ )
2F7/2
- GROUND STATE ( Yb3+ )
Up conversion
Photon

8. 3. Down conversion in solar cell
 Splitting of one high energy photon
in two low energy photons
 It’s a linear process
Down conversion is beneficial for solar cells with small gap
where the thermalization is major factor.
 Wider portion of the solar spectrum
Solar cell
Down converter
Sun
Fig. 5 Down–converter with solar cell
[ https://www.researchgate.net/publication/224568913_Downconvers ]

9. 3.1 Working principle for down conversion
4F7/2 - EXCITED STATE ( Er3+ )
2F7/2
2F5/2
- EXCITED STATE ( Yb3+ )
- GROUND STATE ( Yb3+ )
Fig. 6 energy state of lanthanide ion and mechanism for DC
PHOTON
Down conversion
[ https://www.researchgate.net/publication/224568913_Downconvers ]

10. 4 Spectral conversion
Fig. 5 spectral conversion design for PV application
1. Down-shifting
2. Quantum-cutting
3. Up-conversion (NIR – Visible or UV)
(UV or Visible – NIR )
Spectral Wavelength Energy
Ultraviolet 10nm-400nm 124ev-3.3ev
Visible 400nm- 700nm 3.3ev-1.7ev
Infrared 700nm-1mm 1.7ev-1.24mev [ Enhancing solar cell efficiency- Xiaoyong Huang, sanyang Han ]

11. 5. Material choice for Up-conversion and down-conversion
 Lanthanide ions or couple of ions ( Yb3+ , Er3+ )
Yb3+ works as absorber ( sensitizer )
Er3+ Emits the photon with high energy ( up conversion )
Yb3+ ( down conversion )
 Nano crystal ( NaYF4:Er3+, Yb3 )
( Phosphate and fluoride )
 Nano crystals is transparent solution

12. 6. Efficiency improvement ( UC and DC )
 Shockely–Queisser limit for single junction silicon solar cell is 31% for non concentrated sun
light.
 Trupke, Green and Wurfel– first performed the potential of increasing the efficiency through up
conversion and down conversion ( 47.6 % , non concentrated )
 With an ideal downconverter material ( 2 Eg into two photons that both can be absorbed ) , limit of
efficiency of 40% is possible for a solar cell with a band gap of 1.1 eV.
 Band gap (2 eV ) with solar , an ideal up converter can raise the upper limit of the conversion
efficiency to 50%.

13. 7. Other importance of UC and DC
1. By using UC we can use low energy photon to produce the more electricity
2. We can reduce the thermalization loss by suing DC
3. Improvement of stability of other thin film technologies such perovskite &
organic solar cells ( by down conversion of UV light ), increment harvesting of
UV.

14. References
(1) van Sark, W. G., de Wild, J., Rath, J. K., Meijerink, A., & Schropp, R. E. (2013). Upconversion in
solar cells. Nanoscale research letters, 8(1), 1-10.
(2) Van Der Ende, B. M., Aarts, L., & Meijerink, A. (2009). Lanthanide ions as spectral converters for
solar cells. Physical Chemistry Chemical Physics, 11(47), 11081-11095.
(3) https://www.researchgate.net/publication/224568913_Downconvers
(4) Dong, J., Gao, W., Han, Q., Wang, Y., Qi, J., Yan, X., & Sun, M. (2019). Plasmon-enhanced
upconversion photoluminescence: Mechanism and application. Reviews in Physics, 4, 100026