Perovskite solar cells (PSCs) are a promising third generation solar cell technology that can be produced at low cost with high efficiencies. PSCs use a perovskite crystalline structure as the light absorber layer, such as methylammonium lead iodide. Since their introduction in 2009 with an efficiency of 3.8%, PSC efficiencies have rapidly increased to over 22% due to improved materials and device architectures. While still facing challenges such as stability, PSCs have the potential to dramatically reduce the cost of solar electricity if further developed and commercialized.

1. PEROVSKITE SOLAR CELLS
Center For Materials Engineering
By Kidist Worku
July,2019

2. INTRODUCTION
• Perovskite
• CaTiO3
• Perovskite structure
• Generic form ABX3
perovskite crystal Perovskite structure

3. CONT’
• Perovskite solar cells emerged as third generation solar cells.

4. CONT’
• Perovskite crystalline systems

5. CONT’
• Organometal halide perovskites, (e.g. methyl ammonium lead
iodide, MALI)
• Low cost, high efficiency solar cells
• MALI-based devices -introduced in 2009 PCE of 3.8%
• PSCs yielding PCE of up to > 20% in 2016

6. STRUCTURE OF PSCS
• Pseudo cubic lattice arrangement
• Large atomic or molecular cation (positively-charged) of type A in the
centre
• The corners occupied by atoms B (also positively-charged cations)
• Faces of the cube are occupied by a smaller atom X with negative charge
(anion).

7. CONT’
• Depending on which atoms/molecules are used in the
structure, perovskites can have an impressive array of
interesting properties, including
• Superconductivity,
• Spin-dependent transport (spintronics) and
• Catalytic properties.

8. PSC STRUCTURE
• Fluorine-doped tin oxide (FTO)/glass substrate
• TiO2 layer (TCO) = ETM
• CH3NH3PbI3 perovskite
• Spiro-MeOTAO = HTM
• Metallic electrodes (Au, Ag…)

9. CONSTRUCTION
PSC materials architecture
• Two most common PSC architectures
• Mesoscopic
• Planar
• Inverted architecture

10. CONT’
• Device configurations
• Transparent conducting glass
• hole- or electron-selective layer
• perovskite
• Front and back contact.

11. SEM IMAGE FOR PSC

12. MATERIAL CHOICE FOR PSC CONSTRUCTION
• .Transporters (HTM
& ETM)
• Charge carrier selectivity
• Matching of energy levels
• Degree of chemical
interaction
• Conductivity
• Light absorption
Contacts
• Light absorption
• Work function
• Chemical
contamination
Back Contact Electrode:
Gold; work function -5.1 eV
Silver; work function -4.26 eV
Aluminum; work function - 4.28
eV
Transparent Conductive Front
Contact:
Fluorine-doped tin oxide (FTO);
(work function: -4.4 eV)
Indium tin oxide (ITO);
(work function: -4.8 eV)

13. SYNTHESIS OF PSCS
• Simple and cost effective
• Two methods of processing
• variety of solvent techniques
• vapour deposition techniques.

14. • One step coating: CH3NH3I and
PbI2 are dissolved (ex. in gamma-
butyrolactone (GBL)),applied as
coating solution, drying and
annealing, spin coated
• Two step coating: TiO2 substrate
PbI2 solution is coated, form PbI2
film, then 2-proponol solution of
CH3NH3I is added to spinning
PbI2 film.
SOLUTION PROCESS TECHNIQUE

15. • Thermal evaporation technique requires high vacuum
condition
VAPOUR ASSISTED SOLUTION PROCESS

16. CHALLENGES AND PROGRESSES
• 1999, Tokyo, Japan- optical absorption layer for a solar cell using a
rare-earth-based perovskite compound.
• 2009, introduced CH3NH3PbI3 and the larger-bandgap analogue
CH3NH3PbBr3 as sensitizers for liquid-electrolyte-based DSSCs,
• The power conversion efficiency 3.8%, poor device stability due
to the rapid dissolution of the perovskite in the organic solvent.
• 2011- changing both the electrolyte formulation and the method of
depositing the perovskite, performance and stability attaining a PCE
of 6.5%
• 2014 -replaced electrolyte with a solid state hole conductor (or hole-
transporting material, HTM),
• PCE double, stability improved

17. CONT’
• Mesoporous scaffold made of Al2O3 instead of TiO2 produced similar if
not better, conversion efficiencies, even though Al2O3 is unable to assist
in electron extraction due to its large bandgap. (Lee et al, )
• This suggested that the perovskite itself transported the electrons. In
just a few years, PSCs have achieved cell efficiency surpassing the 22%
mark in 2016.
• PSC efficiencies have increased more rapidly than any other PV
technology, from 3.1% in 2009 to over 22.1% in 2016

18. DRAW BACKS OF THE CURRENT TECHNOLOGY
Moisture content
• Degradation of the HTM layer
• TiO2 nanoparticles can act as moisture barrier
• TiO2 act as photo catalyst and promote the degradation
of CH3NH3PbI into CH3NH2 and HI

19. CONT’
• Stability
• Humidity
• High temperature
• Formamidinium(FA) and partially replacing I- with Br-,
• Toxicity
• CH3NH3PbI3 in contact with polar solvents such as
water can convert to PbI2,
• moderately water-soluble, carcinogen, toxic

20. PSC MARKET
• Perovskite, a dirt-cheap material
• Cut the cost of a watt of solar-generating capacity by three-
quarters.
• This means that solar panels would cost just 10–20 cents per
watt.
• Top producers of PSCs