Advances in Quantum Dot-Sensitized Solar Cells

Bingze Li

South China University of Technology, School of Materials Science and Engineering, Guangzhou, Guangdong, China

Keywords: Quantum Dot-Sensitized Solar Cells, Polysulfide Electrolyte, Photovoltaic Conversion Efficiency, ZCISe

Quantum Dots, Semi-Solid Electrolyte.

Abstract: Quantum dot-sensitized solar cells (QDSSCs), as the third generation photovoltaic devices, have become an

important direction to break through the efficiency limit of traditional silicon-based solar cells by virtue of

their high theoretical efficiency (~44%), low preparation cost, and wide spectral absorption range. This paper

focuses on the latest research progress of the four core components of QDSSCs (photoanode, quantum dot

sensitizer, electrolyte system, and counter electrode materials). By modifying black titanium dioxide and

heterostructured composite photoanodes (e.g., TiO2@ZnO, g-C3N4@TiO2), the photoelectron transfer

efficiency of photoanodes has been significantly improved, with the highest photoelectric conversion

efficiency (PCE) of 9.11%. The application of organic chalcogenide quantum dots has led to a PCE exceeding

18%, while novel deposition techniques (e.g., CLIS/DA method) have enabled the more conventional ZCISe

quantum dot cell to exceed 17% PCE, while improving its stability. Solid/quasi-solid electrolytes (e.g.,

polysulfide gels, Ce-doped LaMnO3) effectively solve the problem of volatilization and corrosion of liquid

electrolytes, and improve PCE by 33%. High entropy sulfide and metal-organic framework derived pairs of

electrode materials further optimized the catalytic performance and cell efficiency. Although the lab

efficiency is close to 8%, the long-term stability (thousand-hour test limit) and scale-up production of

QDSSCs are still key challenges.

1 INTRODUCTION

Driven by the global energy structure transition and

carbon neutrality goals, solar energy has become a

core solution to alleviate fossil energy dependence

and environmental pollution. Currently, traditional

silicon-based solar cells dominate the solar

photovoltaic (PV) market, but their photovoltaic

conversion efficiency is close to the theoretical limit

(~29%), and their production suffers from difficulties

in the production of high-purity monocrystalline

silicon feedstock, as well as high energy consumption

for production.

Quantum dot sensitized solar cells (QDSSCs), as

the third generation of solar cells derived from dye-

sensitized solar cells (DSSCs), are characterized by a

simple manufacturing process and relatively

inexpensive raw materials. Moreover, quantum dots

(QDs), with their quantum-limited-domain effect,

size-dependent energy band tunability, and multi-

exciton generation (MEG) properties, can achieve

https://orcid.org/0009-0001-4427-8907

efficient absorption of the full wavelength of the solar

spectrum, which results in a theoretical upper limit of

the efficiency of quantum dot-sensitized solar cells as

high as about 44%, which is much higher than the S-

Q limit of 33.7% for single-junction cells. In recent

years, with the increasing research on QDSSC, its

laboratory efficiency has been increased to more than

18%, showing great potential for application.

However, this efficiency still falls short of that of

single-junction silicon-based cells, and its stability,

flexibility, and environmental toxicity need to be

improved urgently.

The main direction of research on QDSSCs lies in

the targeted optimization of each structure of

QDSSCs, and this paper will outline the research

progress of QDSSCs in terms of each core component

in the QDSSCs assembly respectively, and by

summarizing the latest and advanced research results,

this paper aims to provide researchers with the ideas

to advance the QDSSCs from the laboratory to

industrialization.

Li, B.

Advances in Quantum Dot-Sensitized Solar Cells.

DOI: 10.5220/0013861400004708

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 2nd International Conference on Innovations in Applied Mathematics, Physics, and Astronomy (IAMPA 2025), pages 659-663

ISBN: 978-989-758-774-0

659

2 STRUCTURE AND PRINCIPLE

OF QDSSCS

As shown in Figure 1, the main structure of QDSSCs

consists of quantum dots, photoanode, electrolyte and

counter electrode. Among them, quantum dots are a

nanoscale semiconductor material with a size-

dependent energy band structure, which can be tuned

in size to achieve precise adjustment of light

absorption or emission wavelength. As the main

absorbing structure of sunlight, quantum dots

produce electron-hole pairs after absorbing light

energy. The photoanode is the electrode that absorbs

light energy and injects photogenerated electrons into

the external circuit, often composed of

semiconductors such as TiO₂, which assumes the

function of electron generation and transmission in

photoelectrochemical devices and is a good loading

platform for quantum dots, and accepts

photoelectrons generated by the QDs, and then

transmits the photogenerated electrons to the counter

electrode via the conductive glass and the external

circuit. The counter electrode is used to receive

electrons from the external circuit and catalyze the

reduction of oxidized species in the electrolyte, thus

closing the circuit and keeping the system running.

The photogenerated holes are transferred to the

electrolyte, which is the ionic conductor connecting

the photoanode to the counter electrode and is

responsible for transporting ions to maintain charge

balance and complete the redox cycle. Finally, the

electrolyte accepts electrons from the external circuit

through the counter electrode and is reduced, thus

completing the battery cycle.

Figure 1: Schematic structure of quantum dot sensitized

solar cells (QDSSCs) (Photo/Picture credit: Original).

3 PERFORMANCE AND

OPTIMIZATION OF QDSSCS

The core performance indicators of QDSSCs cover

photoelectric conversion efficiency (PCE), open-

circuit voltage (Voc), short-circuit current (Jsc), fill

factor (FF), and stability. Among them, photoelectric

conversion efficiency (PCE) is the most important

indicator for evaluating solar performance, reflecting

the ability of the cell to convert light energy into

electricity. The open-circuit voltage determines the

voltage output of the cell in the open-circuit state,

while the short-circuit current is directly related to the

number of photogenerated carriers, both of which

together affect the output performance of the cell. The

fill factor = (maximum output power) / (Voc × Jsc)

reflects the cell output characteristics. In addition,

stability is crucial for the practical application of

QDSSCs, which determines the lifetime and

reliability of the cell, which can be effectively

improved by means of adopting antioxidant quantum

dots and encapsulation technology.

3.1 Photoanode

In QDSSCs, the ideal photoanode should have more

attachment sites for quantum dots, lower

compounding rate of photogenerated electrons, and

excellent electron injection and transfer capability.

Among them, TiO2, as a wide bandgap

semiconductor, is still the most widely used

photoanode material due to its excellent chemical

stability, non-toxicity, low cost and relatively fast

electron transfer rate (Akash, Shwetharan & Kusuma,

2022). The current research on TiO2 mainly lies in

the further doping or compounding of TiO2

nanomaterials with different morphologies that have

been explored.

Black titanium dioxide possesses higher

photocatalytic activity due to its abundant oxygen

defects and Ti3+. Jiang et al. (2024) and Yao et al.

(2022) conducted studies on black TiO2

nanoparticles for the fabrication of photo-anodes for

QDSSCs, respectively, where Jiang et al. (2024) used

the black TiO2 produced by hydrogenation reduction

as the photo-anode to achieve the FF and short-circuit

current density (Jsc) obtained an enhancement of

about 30%, which led to an enhancement of the final

PCE by about 71% to 5.3% when all other conditions

remained unchanged. On the other hand, Yao et al.

(2022) prepared black TiO2 for the assembly of

QDSSCs by modifying TiO2 of different crystal types

under femtosecond laser, and the PCE of QDSSCs

assembled with rutile TiO2 was as high as 9.11%,

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which is 2.27 times higher than that of the pristine

TiO2 QDSSCs, by laser-modifying rutile TiO2 to

black TiO2 in ethanol. Regarding the composite TiO2

materials, Li et al. investigated the TiO2

heterostructure composite photoanodes, Li et al.

(2024) fabricated hexagonal nanopillar array

photoanodes with TiO2-coated ZnO heterostructure

and TiO2 nanorods with g-C3N4@TiO2

heterostructure, which resulted in a higher PCE of

QDSSCs compared to simple ZnO nanopillar array

photoanodes and TiO2 photoanodes, respectively.

anodes resulted in 25% and 17% enhancement in PCE

of QDSSCs, respectively, and increased the stability

of the photoanodes (Li et al., 2024). The above

studies show that TiO2 has the advantages of good

photocatalytic performance, chemical stability, non-

toxicity and environmental protection, and low price,

which is widely used in the fields of wastewater

treatment, air purification, and photocatalytic

hydrogen production. However, it only responds

under ultraviolet light, and the photogenerated

electrons and holes are easy to compound, which

limits its catalytic efficiency. Through metal/non-

metal doping, noble metal deposition, semiconductor

composite, dye sensitization and other modification

means, it can effectively broaden the light response

range, enhance the electron separation ability, and

significantly improve the photocatalytic activity.

Modified TiO₂ materials also exhibit excellent visible

light catalytic ability and cyclic stability. Future

development directions include enhancing visible

light utilization efficiency, developing multi-

component synergistic modification technology,

enhancing material stability and reusability,

exploring green and low-consumption synthesis

processes, as well as in-depth study of photocatalytic

reaction mechanisms, etc., in order to achieve more

efficient and wider environmental and energy

applications.

3.2 Quantum Dot Sensitizers

The optimization of quantum dot sensitizers for

QDSSCs mainly lies in the optimization of the design

of the quantum dots themselves and the optimization

of the quantum dot deposition method. Aqoma et al.

(2024) designed a type of perovskite-based CQDs

(PQDs) based on organocation cationic groups with a

narrower bandgap, and adopted a ligand-exchange

strategy based on ammonium iodide to enhance the

surface passivation effect of PQDs by replacing long-

chain oleyl ligands to improve their photovoltaic

performance and long-term stability. A ligand

exchange strategy was employed to enhance the

surface passivation of the PQDs by substituting long-

chain oleyl ligands to improve their photovoltaic

properties and long-term stability. The QDSSCs

assembled with such organic PQDs obtained the

highest PCE of up to 18.1% in the laboratory so far

and had a photostability of 1200 h. Wang et al. (2025)

deposited water-soluble ZCISSe QDs on TiO2

nanorods substrates by first using a once-capped

ligand-induced self-assembly chemical deposition

method (CLIS method), and then on this basis by

direct deposition method (DD method). The oil-

soluble ZCISSe QDs were deposited on the substrate

by direct deposition (DA method), which increased

the quantum dot loading. Meanwhile, in this device,

the photoanode is passivated by the quantum dots

themselves, so the device can reduce the introduction

of surface engineering reagents, lower the fabrication

cost of the device, and effectively suppress the

undesired charge complexation at the

photoanode/electrolyte interface, as well as improve

the stability of the device. The QDSSCs obtained by

this method of deposition obtained a PCE of up to

17.01%, which is the highest efficiency among the

existing liquid junction QDSSCs. Quantum dot

sensitizers in QDSSCs have the advantages of tunable

bandgap, wide range of light absorption and multi-

exciton generation, which can significantly enhance

the photoelectric conversion efficiency. Its

performance can be further enhanced by optimizing

the quantum dot structure and deposition method. In

the future, novel quantum dot material design,

surface-interface engineering optimization and

scalable deposition process can be used to achieve

high-efficiency, low-cost and long-term stable

QDSSCs.

3.3 Electrolyte System

The liquid electrolyte in conventional QDSSCs faces

common problems such as volatilization, leakage and

corrosion. For the electrolyte system of QDSSCs, the

current research hotspot is to improve the long-term

stability of the battery and reduce the encapsulation

requirement of the battery by switching to solid-state

or quasi-solid-state electrolytes for QDSSCs

(Prajapati et al., 2020). Wang et al. (2025) combined

traditional polysulfide electrolytes with sodium

alginate, and obtained quasi-solid-state polysulfide

gel electrolytes. ZCISe QDSSCs assembled with

them obtained a PCE of 8.85%, which is 6% higher

than the PCE of liquid polysulfide under all other

conditions being equal, and they are 3.2 times more

stable than the liquid polysulfide electrolyte QDSSCs,

as well as being more environmentally friendly. The

Advances in Quantum Dot-Sensitized Solar Cells

661

same research team fabricated quasi-solid polysulfide

electrolytes by spin-coating Ce-doped LaMnO3 hole-

transporting materials on semiconductor photoanodes,

drying them, and then immersing them in polysulfide

electrolyte (Wang etl al., 2025). The PCE of the

assembled QDSSCs reaches 9.14%, which is 33%

higher than that of the same standard liquid

electrolyte QDSSCs, and the lifetime is 5% higher,

and the QDSSCs show significant stability

advantages over the liquid electrolyte QDSSCs in

other aspects. Current research focuses on the

development of solid or quasi-solid electrolytes,

aiming to improve environmental adaptability and

packaging simplicity. For example, quasi-solid

polysulfide electrolytes can be constructed by

introducing sodium alginate gels or LaMnO₃-doped

hole-transporting materials, which can significantly

enhance stability and environmental friendliness

while improving PCE. The future development

direction should focus on the design of quasi-solid-

state or solid-state systems with high conductivity,

low cost, and scalability.

3.4 Counter Electrode Materials

The main role of the counter electrode is to collect the

electrons from the external circuit and transfer them

to the electrolyte by catalytic reduction oxidation of

the electrolyte. Ideal electrode materials should

satisfy the following properties: 1) simple and low-

cost preparation process; 2) good electrical

conductivity and high catalytic activity; and 3)

excellent chemical stability in the electrolyte

environment. Wang et al. (2025) prepared high-

entropy metal sulfide nanoparticles with the

composition of (CdCuCoMnZn)Sx by the solution

method and coated them directly on the FTOs by

using screen-printing technique. The QDSSCs

assembled in this way had an open-circuit voltage of

0.665 V and a high FF of 0.49, and the

electrocatalysts were obtained by cyclic voltammetric

stability test to have better electrochemical stability

than other sulfide electrocatalysts, demonstrating the

potential of high-entropy polysulfides as a pair of

electrode materials for QDSSCs. Zhang et al. (2025)

on the other hand, annealed ZIC-64 organometallic

metal by high temperature framework, and then

attaching MoS2 by vapor deposition to make the base

material of the counter electrode, and finally

depositing it on the mesoporous carbon supported by

titanium mesh to produce a high-performance counter

electrode. The QDSSCs assembled with the counter

electrodes made of this material and ZCISe have a

PCE of up to 16.39% and an excellent filling factor of

up to 0.735.

The counter electrode plays a key role in QDSSCs

to collect electrons and catalyze the reduction of

electrolyte, and excellent counter electrode materials

need to be highly conductive, catalytically active,

chemically stable, and cost-effective. Nevertheless,

the current non-precious metal catalytic materials still

have limitations such as insufficient electrical

conductivity, unstable catalytic sites, and

complicated device preparation processes, which

affect their promotion in commercialization. Future

development should focus on the construction of

multifunctional composite structures, the precise

regulation of catalytic activity centers, the

development of scalable and low-cost preparation

processes, and the exploration of materials that take

into account high performance and environmental

friendliness, in order to promote the industrialization

of highly efficient, stable, and sustainable QDSSCs.

4 CONCLUSION

Quantum dot-sensitized solar cells are the most

competitive third-generation solar cells in the energy

market due to the low cost of raw materials as well as

the simplicity of the fabrication process, and their

research history breaks the stereotype that

semiconductor photovoltaic devices require high-

purity, high-quality semiconductors. Currently, a

variety of quantum dot-sensitized solar cells with

photovoltaic conversion efficiencies of 16% or more

have been fabricated in the laboratory, with

efficiencies much higher than those of commercially

available, inexpensive thin-film solar cells and

polycrystalline silicon semiconductor cells, and the

structures and theories of the various components

have been matured.

As far as the present situation is concerned, the

initial exploration of the marketable and

industrialized production of QDSSCs based on ZCISe

and organic chalcogenide quantum dots is ready to

start. However, the stability test experiments of

QDSSCs in the current research are limited to the

thousand-hour level, and in the future, it is necessary

to combine multi-scale simulation modeling

techniques (e.g., first-principle calculations and

device-level degradation simulations) to predict the

degradation mechanism of the material interfaces and

the environmental tolerance, and to provide

theoretical guidance for the long-life design, in order

to carry out simulation prediction of the stability of

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QDSSCs for years or even decades of use. Simulation

prediction.

Looking ahead, QDSSCs have the potential to

shine in new application scenarios such as flexible

electronics, building-integrated photovoltaics, and

low-light environment energy systems. Their low-

cost and easy-to-prepare characteristics also allow

QDSSCs to provide energy security for people in

poor production conditions, such as in disaster areas

and on other planets.

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