Fused-ring electron acceptor as an efficient interfacial material for planar and flexible perovskite solar cells
Graphical abstract
Introduction
Perovskite solar cells (PSCs) have become a research hotspot in the field of photovoltaics due to their fast-growing power conversion efficiency (PCE) [1], low cost, and solution processability [2,3]. Recently, the certificated PCE of PSCs reaches over 25% [[4], [5], [6]], which is exceeding copper indium gallium selenium and cadmium telluride solar cells and approaching the record of silicon-based solar cells. Inorganic-organic perovskite possesses advantages of adjustable band gap and high carrier mobility of both electrons and holes, so it is suitable for fabricating the photovoltaics devices with planar architecture. In a typical planar PSCs, perovskite layer is sandwiched between an electron transport layer (ETL) and a hole transport layer (HTL) to construct an n-i-p stacked structure. Traditional electron transport materials include TiO2, SnO2, ZnO and fullerene and its derivatives [7]. The transport layers are found to be critical to the PCE and long-term stability of PSCs [8,9]. For example, as the most widely used ETL, anatase-type TiO2 has been extensively employed for highly efficient PSCs due to its excellent optical transmittance, semiconductor characteristics, and chemical stability [[10], [11], [12]]. However, its rough surface with a large number of surface defects leads to serious charge recombination and large leakage current, resulting in efficiency loss and nonnegligible hysteresis effect [13,14]. Besides, TiO2 would catalyze the decomposition of perovskite and decrease the stability of PSCs under ultraviolet irradiation. Therefore, many efforts have been devoted to improving the properties and modifying the surface of TiO2 to obtain PSCs with high efficiency and stability. The approaches of optimization include element doping, surface treatment, nanocomposite assembly and interface engineering [[15], [16], [17], [18]]. Interface engineering focuses on the construction of an interlayer between TiO2 and perovskite, such as fullerene and its derivatives, to promote electron extraction and passivate the trap states [[19], [20]]. Recently, several non-fullerene fused-ring electron acceptors (FREAs) have also been introduced into n-i-p perovskite solar cells as the interfacial modifier [[21], [22], [23]], which are less expensive and have better affinity to the substrate than fullerenes. The FREAs are used as the electron acceptors in organic solar cells and their structures are based on an electron donating fused ring with strong electron withdrawing groups, which contributes to adjustable optical band gap and energy level structure, good electronic transfer capability, excellent thermal and photochemical stability [21,22]. The application of FREAs in PSCS not only increases the PCE but also improves the long-term stability of devices, which is regarded as one of the effective approaches to further improve the PSCs performance.
In this paper, a typical FREAs, ITIC, is deposited on top of TiO2 film as the interfacial modifier for planar PSCs with forward structure. ITIC has a well-match LUMO energy level (−3.93 eV) to the perovskite (Fig. 1) and good electron transport ability [23]. The influence of ITIC on the morphology of perovskite crystals and the electrical properties of the device are studied comprehensively. The devices with the structure of ITO/TiO2/ITIC/(FAPbI3)X(MAPbCl3)1−x/spiro-OMeTAD/Ag are successfully fabricated. The PSCs on the rigid substrate obtain a highest PCE of 19.61% which is much higher than 16.99% of the reference device without ITIC, and the hysteresis effect is significantly reduced. The modified ETL is low-temperature solution processable, which is compatible with the plastic substrate. The ITIC-based flexible devices is thus fabricated and a champion PCE of 14.87% is achieved. The flexible device remains 80% of its original PCEs after 500h stored in ambient humidity of 30–40%, which shows significantly superior stability to the unmodified device.
Section snippets
Materials
Lead (II) iodide (PbI2) (99.999%) was purchased from AlfaAesar.Titanium(IV) isopropylate (TTIP) (97%), formamidinium acetate salt (99%), hydroiodic acid (HI) (57 wt%), anhydrous dimethylformamide (DMF) (99.8%), methylamine hydrochloride (MACl), anhydrous dimethyl sulfoxide (DMSO) (99.9%), acetonitrile(99.8%), chlorobenzene (99.8%), 4-tertbutylpyridine (4-tBP) (96%), and bis(trifluoromethane) sulfonimide lithium salt (Li-TFSI) (99.95%) were purchased from Sigma-Aldrich. ITIC and
Effect of ITIC on TiO2
In order to study the effect of ITIC, ITIC with different thickness is deposited on TiO2 by spin coating with different spin speed. 6000 r/min, 5000 r/min, 4000 r/min, 3000 r/min and 2000 r/min are applicated, corresponding to an increasing thickness of ITIC on TiO2. The reference sample based on pristine TiO2 is fabricated by an annealing-free aqueous process. A Hall effect measurement system is employed to test the effect on the electrical properties of these films, and the results are listed
Conclusion
In summary, the fused ring electron acceptor ITIC is deposited on the conventional ETL TiO2 as the interfacial modifier. ITIC fills the cracks and suppresses the defects of TiO2 surface, which restrains the charge accumulation and recombination at the interface. Due to the decreasing hydrophilicity of the surface, large perovskite crystals with high quality can be obtained on the modified ETL. Therefore, the PCE of the PSCs reaches 19.61% on the rigid substrate and 14.87% on the flexible
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by National Natural Science Foundation of China (61605164 and 61705258), and the Fundamental Research Funds for the Central Universities (20720190027).
References (37)
- et al.
Efficient planar heterojunction perovskite solar cells with Li-doped compact TiO2 layer
Nanomater. Energy
(2017) - et al.
Low-temperature-processed ZnO–SnO2 nanocomposite for efficient planar perovskite solar cells
Sol. Energy Mater. Sol. Cells
(2016) Best Research-Cell Efficiency Chart
- et al.
Solvent engineering for high-performance inorganic-organic hybrid perovskite solar cells
Nat. Mater.
(2014) - et al.
Simplification of device structures for low-cost, high-efficiency perovskite solar cells
J. Mater. Chem. A.
(2017) - et al.
Stable perovskite solar cells with efficiency exceeding 24.8% and 0.3-V voltage loss
Science
(2020) - et al.
Iodide management in formamidinium-lead-halide-based perovskite layers for efficient solar cells
Science
(2017) - et al.
Efficient perovskite solar cells via improved carrier management
Nature
(2021) - et al.
The rapid evolution of highly efficient perovskite solar cells
Energy Environ. Sci.
(2017) - et al.
Structure of methylammonium lead iodide within MesoporousTitanium dioxide: active material in high-performance perovskite SolarCells
Nano Lett.
(2014)
Role of Metal Oxide Electron-Transport Layer Modification on the Stability of High Performing Perovskite Solar Cells
ChemSusChem.
Enhanced photoluminescence and solar cell performance via Lewis base passivation of organic-inorganic lead halide perovskites
ACS Nano
Understanding the rate-dependent J-V hysteresis, slow time component, and aging in CH3NH3PbI3 perovskite solar cells: the role of a compensated electric field
Energy Environ. Sci.
Efficient planar heterojunction perovskite solar cells by vapour deposition
Nature
Charge selective contacts, mobile ions and anomalous hysteresis in organic-inorganic perovskite solar cells
Mater. Horiz.
Improving the extraction of photogenerated electrons with SnO2 nanocolloids for efficient planar perovskite solar cells
Adv. Funct. Mater.
All-solid perovskite solar cells with HOCO-R-NH3+I– anchor-group inserted between porous titania and perovskite
J. Phys. Chem. C
Hysteresis and transient behavior in current-voltage measurements of hybrid-perovskite absorber solar cells
Energy Environ. Sci.
Cited by (4)
Caffeine additive based nanoarchitectonics of methylammonium lead iodide (MAPbI<inf>3</inf>) perovskite solar cell device: investigations on charge carrier properties using AC impedance spectroscopy
2023, Journal of Materials Science: Materials in ElectronicsPerovskite solar cells: recent progress and strategies developed for minimizing interfacial recombination
2022, Frontiers of Materials ScienceBroad-Band-Enhanced Plasmonic Perovskite Solar Cells with Irregular Silver Nanomaterials
2022, ACS Applied Materials and InterfacesFlexible Perovskite Solar Cells: From Materials and Device Architectures to Applications
2022, ACS Energy Letters
- 1
These authors contributed equally to this work.