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LUND UNIVERSITY LIBRARIES

Solvent Vapor Annealing-Driven Performance Enhancement of Lead-Free Cs3Bi2-xSbxI9 Perovskite Solar Cells

Alissa, Saher LU (2025) KEMR30 20251
Department of Chemistry
Abstract
Solar energy is one of the most promising solutions for the energy crisis due to its wide availability and cost-effectiveness. Solar cells have long been used to convert solar energy to electricity, but due to the high cost and difficult processability of the widely available and commercialized silicon solar cells, replacing them with new technology has always been of interest for researchers. Recently, perovskites have emerged as a new class of semiconductors showing good optoelectronic properties making them potential contenders for the traditional solar cells. However, the high-performance perovskite solar cells are a water-soluble source of lead suffering from human and environmental toxicity and instability implying a need to replace... (More)
Solar energy is one of the most promising solutions for the energy crisis due to its wide availability and cost-effectiveness. Solar cells have long been used to convert solar energy to electricity, but due to the high cost and difficult processability of the widely available and commercialized silicon solar cells, replacing them with new technology has always been of interest for researchers. Recently, perovskites have emerged as a new class of semiconductors showing good optoelectronic properties making them potential contenders for the traditional solar cells. However, the high-performance perovskite solar cells are a water-soluble source of lead suffering from human and environmental toxicity and instability implying a need to replace it.

Pnictogens such as Bi, and Sb have gained increased attention as lead-free alternatives due to their lower toxicity and higher stability. Despite numerous efforts to enhance their performance in PSCs, these materials still suffer from low efficiency under 1 Sun conditions due to large bandgaps, low dimensionality, poor morphology, and recombination losses. These limiting aspects make them more suitable for indoor photovoltaics because of its narrower spectrum. Cs3Bi2I9 is one of the investigated lead-free alternatives showing 1.09% PCE under 1 Sun light conditions when applied in the standard n-i-p architecture. Further improvements were made by using a dissolution-recrystallization method and defect passivation strategies. However, the ion substitution strategy that has proven effective in improving efficiency of Pb PSCs, has not been investigated as a potential way to enhance the performance of Cs3Bi2I9 solar cells. Incorporation of Sb into Cs3Bi2I9 can potentially enhance the morphology of Cs3Bi2I9 by enhancing the crystallization and altering its dimensionality. In addition, a bandgap modulation of Cs3Bi2I9 is also possible through Sb alloying.

The aim of this project is to investigate the possibility of tailoring the optoelectronic properties of Cs3Bi2I9 through Sb alloying by bandgap modulation, morphology improvement, and inducing a dimensional transition from 0D to 2D. This is done by optimizing Cs3Bi2-xSbxI9 thin films for photovoltaic applications. Thin films and the resulting photovoltaic devices are fabricated by the solution-processing spin-coating method, and the compact TiO2 (c-TiO2) electron transport layer (ETL) is deposited using a spray pyrolysis setup. The absorption spectra of these films are measured by an ultraviolet-visible (UV-Vis) spectrophotometer, the structural analysis is done using X-ray diffraction (XRD), elemental analysis is performed by energy dispersive x-ray spectroscopy (EDX), and morphology images are recorded by scanning electron microscopy (SEM).

Sb was successfully incorporated into Cs3Bi2I9 using the solvent vapor annealing (SVA) method, whereas direct incorporation via SbI3 addition to the precursor solution was less effective in achieving the desired structural and optoelectronic modifications. Both devices made using the SVA method and Cs3Bi1.50Sb0.50I9-based devices successfully improved the performance of the solar cells compared to Cs3Bi2I9-based devices by improving the open-circuit voltage (VOC) and short-circuit current density (JSC).

Future work may focus on enhancing the photovoltaic performance by optimizing the annealing temperature for both pristine Cs3Bi2I9 and Sb-alloyed Cs3Bi2-xSbxI9 compositions, refining the SVA process parameters, and exploring multi-cation substitution at the B-site or halide anion engineering to further tailor the material’s optoelectronic properties. (Less)
Popular Abstract
Substituting fossil fuels with more environmentally friendly energy sources is a well-known solution to the emissions of green-house gases (GHGs) and the resulting global warming. A class of new prospective materials that recently emerged as promising semiconductors is metal halide perovskites (MHPs) having the general chemical formula ABX3, where A is a positively charged metal cation, B is a divalent metal cation, and X is a negatively charged anion commonly from group 17 in the periodic table. Over the past two decades, MHPs have demonstrated remarkable efficiency gains in solar cell applications, with performance improving from 3.8% to 27.3% within just 15 years. This rapid advancement positions perovskite solar cells (PSCs) as strong... (More)
Substituting fossil fuels with more environmentally friendly energy sources is a well-known solution to the emissions of green-house gases (GHGs) and the resulting global warming. A class of new prospective materials that recently emerged as promising semiconductors is metal halide perovskites (MHPs) having the general chemical formula ABX3, where A is a positively charged metal cation, B is a divalent metal cation, and X is a negatively charged anion commonly from group 17 in the periodic table. Over the past two decades, MHPs have demonstrated remarkable efficiency gains in solar cell applications, with performance improving from 3.8% to 27.3% within just 15 years. This rapid advancement positions perovskite solar cells (PSCs) as strong contenders to well-established, commercially available silicon-based solar cells, which currently reach efficiencies of around 26.8%, as well as other emerging photovoltaic technologies.

However, the rewarding perovskite semiconductors offering high efficiency in PSCs are based on lead (Pb) which suffers from toxicity and instability towards environmental factors. Therefore, researchers are currently on a race to develop alternative lead-free perovskites to replace lead and make the technology more environmentally friendly. Bismuth (Bi) and antimony (Sb) are two of several other elements being proposed as possible alternatives due to their availability from natural sources and low toxicity. Unfortunately, perovskites based on Bi and Sb do not possess the same desirable intrinsic physical properties as Pb-based perovskites that makes them desirable for the solar cell application. Especially, Bi-based perovskites are much less efficient in solar cells owing to their low dimensionality, large bandgap energy limiting their light absorption ability, and poor morphology affecting the crystallinity of the material.

Nevertheless, the high bandgap energy makes these materials more efficient in absorbing indoor light for powering electronic devices. Cs3Bi2I9 is a zero-dimensional (0D) Bi-based perovskite material that has been applied in PSCs but shown a modest performance due to the limiting aspects mentioned above. This thesis work aims to enhance the efficiency of Cs3Bi2I9 by incorporating Sb ions into the crystal structure of Cs3Bi2I9 aspiring to reduce the bandgap, improve the morphology, and induce a transition from 0D to two-dimensional (2D) phase. By achieving these desired modifications, the performance of photovoltaic devices based on this modified Cs3Bi2-xSbxI9 perovskite can be improved. In this work, the photovoltaic devices based on Cs3Bi2-xSbxI9 are fabricated and their performance is investigated.

The work was done by fabricating Cs3Bi2I9 and Cs3Bi2-xSbxI9 thin films using a spin-coater and investigating their optoelectronic properties. A spin-coater is an instrument used to deposit and distribute liquid materials evenly onto a rigid or a flexible substrate using the centrifugal force. When the thin films were well investigated and optimized, photovoltaic devices were fabricated using the spin-coater to deposit all essential layer except than the compact titanium dioxide (c-TiO2) that was deposited using a spray-pyrolysis setup, a method used to deposit solutions onto substrates at high temperatures by spraying the solution onto them while being heated on a hot plate.

The incorporation of Sb ions into Cs3Bi2I9 lattice structure was done by two different approaches. The first one is the classical way of mixing elements in the perovskite by mixing SbI3 with CsI, and BiI3, the components of the original perovskite when preparing the precursor solution that is coated on glass substrates resulting in thin films. The second approach is by first preparing the original perovskite with its common components, coating it onto glass substrates, and after annealing at 70 ̊C for 15 min, the substrates are transferred into a beaker where small drops of SbI3 are added into the corners of the beaker at 250 ̊C, the beaker is covered, films maintained at 250 ̊C for additional 15 min, the temperature decreased to 200 ̊C for 5 min, and then gradually decreased to room temperature. This is called solvent vapor annealing (SVA) and commonly used to fabricate 2D Cs3Sb2I9.

A decrease of the bandgap was possible using the classical mixing approach, while the SVA method could successfully improve the morphology and in some cases a systematic bandgap modulation was also proven. A transition from 0D to a mixed 0D/2D phase was possible by antisolvent treatment of the pristine Cs3Bi2I9 and the mixed 0D/2D phase was maintained in the Cs3Bi2-xSbxI9 alloyed samples. These modifications resulted in improved performance of the resulting PSCs based on Cs3Bi2-xSbxI9 compared to pure Cs3Bi2I9 films. (Less)
Please use this url to cite or link to this publication:
author
Alissa, Saher LU
supervisor
organization
course
KEMR30 20251
year
type
H2 - Master's Degree (Two Years)
subject
keywords
materials chemistry, perovskite solar cells, lead-free perovskites, clean energy, solvent vapor annealing
language
English
id
9206034
date added to LUP
2025-06-27 11:36:52
date last changed
2025-07-01 11:35:19
@misc{9206034,
  abstract     = {{Solar energy is one of the most promising solutions for the energy crisis due to its wide availability and cost-effectiveness. Solar cells have long been used to convert solar energy to electricity, but due to the high cost and difficult processability of the widely available and commercialized silicon solar cells, replacing them with new technology has always been of interest for researchers. Recently, perovskites have emerged as a new class of semiconductors showing good optoelectronic properties making them potential contenders for the traditional solar cells. However, the high-performance perovskite solar cells are a water-soluble source of lead suffering from human and environmental toxicity and instability implying a need to replace it. 

Pnictogens such as Bi, and Sb have gained increased attention as lead-free alternatives due to their lower toxicity and higher stability. Despite numerous efforts to enhance their performance in PSCs, these materials still suffer from low efficiency under 1 Sun conditions due to large bandgaps, low dimensionality, poor morphology, and recombination losses. These limiting aspects make them more suitable for indoor photovoltaics because of its narrower spectrum. Cs3Bi2I9 is one of the investigated lead-free alternatives showing 1.09% PCE under 1 Sun light conditions when applied in the standard n-i-p architecture. Further improvements were made by using a dissolution-recrystallization method and defect passivation strategies. However, the ion substitution strategy that has proven effective in improving efficiency of Pb PSCs, has not been investigated as a potential way to enhance the performance of Cs3Bi2I9 solar cells. Incorporation of Sb into Cs3Bi2I9 can potentially enhance the morphology of Cs3Bi2I9 by enhancing the crystallization and altering its dimensionality. In addition, a bandgap modulation of Cs3Bi2I9 is also possible through Sb alloying.

The aim of this project is to investigate the possibility of tailoring the optoelectronic properties of Cs3Bi2I9 through Sb alloying by bandgap modulation, morphology improvement, and inducing a dimensional transition from 0D to 2D. This is done by optimizing Cs3Bi2-xSbxI9 thin films for photovoltaic applications. Thin films and the resulting photovoltaic devices are fabricated by the solution-processing spin-coating method, and the compact TiO2 (c-TiO2) electron transport layer (ETL) is deposited using a spray pyrolysis setup. The absorption spectra of these films are measured by an ultraviolet-visible (UV-Vis) spectrophotometer, the structural analysis is done using X-ray diffraction (XRD), elemental analysis is performed by energy dispersive x-ray spectroscopy (EDX), and morphology images are recorded by scanning electron microscopy (SEM). 

Sb was successfully incorporated into Cs3Bi2I9 using the solvent vapor annealing (SVA) method, whereas direct incorporation via SbI3 addition to the precursor solution was less effective in achieving the desired structural and optoelectronic modifications. Both devices made using the SVA method and Cs3Bi1.50Sb0.50I9-based devices successfully improved the performance of the solar cells compared to Cs3Bi2I9-based devices by improving the open-circuit voltage (VOC) and short-circuit current density (JSC).

Future work may focus on enhancing the photovoltaic performance by optimizing the annealing temperature for both pristine Cs3Bi2I9 and Sb-alloyed Cs3Bi2-xSbxI9 compositions, refining the SVA process parameters, and exploring multi-cation substitution at the B-site or halide anion engineering to further tailor the material’s optoelectronic properties.}},
  author       = {{Alissa, Saher}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Solvent Vapor Annealing-Driven Performance Enhancement of Lead-Free Cs3Bi2-xSbxI9 Perovskite Solar Cells}},
  year         = {{2025}},
}