Ligang Yuan

Polyacrylonitrile which has C≡N groups was introduced to passivate the uncoordinated lead cations in perovskite films. The coordination of C≡N with the lead cation was much stronger than that of the normally used C=O group. It could also reduce the I/Pb ratio at the film surface. The device efficiency was improved from 21.58 % to 23.71 %, with the open-circuit voltage enhanced from 1.12 V to 1.23 V.

Abstract

In solution-processed organic–inorganic halide perovskite films, halide-anion related defects including halide vacancies and interstitial defects can easily form at the surfaces and grain boundaries. The uncoordinated lead cations produce defect levels within the band gap, and the excess iodides disturb the interfacial carrier transport. Thus these defects lead to severe nonradiative recombination, hysteresis, and large energy loss in the device. Herein, polyacrylonitrile (PAN) was introduced to passivate the uncoordinated lead cations in the perovskite films. The coordinating ability of cyano group was found to be stronger than that of the normally used carbonyl groups, and the strong coordination could reduce the I/Pb ratio at the film surface. With the PAN perovskite film, the device efficiency improved from 21.58 % to 23.71 % and the open-circuit voltage from 1.12 V to 1.23 V, the ion migration activation energy increased, and operational stability improved.

Publication date: 1 May 2022

Source: Chemical Engineering Journal, Volume 435, Part 2

Author(s): Yuheng Li, Dongyu Fan, Feiyang Xu, Chengwei Shan, Jiahao Yu, Wenhui Li, Dou Luo, Zonghao Sun, Hua Fan, Mengshuai Zhao, Xuehui Li, Kun Cui, Rui Chen, Gongqiang Li, Aung Ko Ko Kyaw

Single-crystal solar cells with high efficiency and a superior weak light response are achieved by engineering the hole extraction interface. Remarkably enhanced efficiency of 22.1% under AM 1.5G irradiation and indoor efficiency of 39.2% under 1000 lux irradiation are obtained, which are both the highest values for MAPbI₃ single-crystal solar cells.

Abstract

Perovskite single crystals have recently been regarded as emerging candidates for photovoltaic application due to their improved optoelectronic properties and stability compared to their polycrystalline counterparts. However, high interface and bulk trap density in micrometer-thick thin single crystals strengthen unfavorable nonradiative recombination, leading to large open-circuit voltage (V _OC) and energy loss. Herein, hydrophobic poly(3-hexylthiophene) (P3HT) molecule is incorporated into a hole transport layer to interact with undercoordinated Pb²⁺ and promote ion diffusion in a confined space, resulting in higher-quality thin single crystals with reduced interface and bulk defect density, suppressed nonradiative recombination, accelerated charge transport, and extraction. As a result, a remarkably enhanced V _OC of up to 1.13 V and efficiency of 22.1% are achieved, which are both the highest values for MAPbI₃ single-crystal solar cells. Moreover, the reduced defect density and suppressed carrier recombination lead to superior weak light response of the single-crystal solar cells after incorporation of P3HT, and an indoor photovoltaic efficiency of 39.2% at 1000 lux irradiation is obtained.

Solar Redox Flow Cells

In article number 2102893, Adélio Mendes and co-workers design, build and test the highest photoactive-area solar redox flow cell (SRFC) device ever reported–The SolarFlow25 cell. This work provides important device design guidelines that will help develop future upscaled SRFCs, a technology that promises to revolutionize energy storage in household/stationary applications given its ability to store and convert sunlight into heat, ready-to-use electricity or even added-value fuels such as hydrogen.

Publication date: 15 May 2022

Source: Chemical Engineering Journal, Volume 436

Author(s): Zhixuan Jiang, Jianfei Fu, Jiajia Zhang, Qiaoyun Chen, Zelong Zhang, Wenxi Ji, Ailian Wang, Taoyi Zhang, Yi Zhou, Bo Song

Ln³⁺-based halide Cs₃TbCl₆ QDs are synthesized and introduced to the interface of perovskite films to promote better bandgap alignment and reduce interface defects density. The Cs₃TbCl₆ QDs modified device has achieved a super high open-voltage of 1.235 V. Cs₃TbCl₆ QDs and black phosphorus dual modified device has yielded a champion photoelectric conversion efficiency of 23.49% and a filling factor of 80.32%.

Abstract

Interfacial engineering is one of the most effective means to improve the photoelectric conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). In this work, Ln³⁺-based halide Cs₃TbCl₆ quantum dots (QDs) are synthesized through a modified hot-injection method, which displays an excitonic emission centered at 431 nm and the characteristic emission peaks of Tb³⁺ ions. Then, the Ln³⁺-based halide Cs₃TbCl₆ QDs are introduced to the interface of Cs_0.05(FA_0.83MA_0.17)_0.95Pb(I_0.83Br_0.17)₃ perovskite films in the PSCs, which can regulate the energy levels, fill the grain boundaries and remove the ionic defects. Surprisingly, the Cs₃TbCl₆ QDs modified devices achieve a champion PCE of 22.89% with a super high open-voltage of 1.235 V. The high open-voltage can be mainly attributed to the better bandgap alignment, enhanced interface, and reduced defects density. Afterward, the hole transport layer (HTL) is modified by the black phosphorus QDs (BPQDs), yielding a champion PCE of 23.49% and a filling factor of 80.32%. The Cs₃TbCl₆ QDs modified unencapsulated device possesses well environmental stability and humidity stability. This work demonstrates a new kind of Ln³⁺-based metal QDs and explores a new approach to fabricate the PSCs with high open-voltage, high efficiency, and good stability through the QD-based passivation techniques.

Publication date: 1 May 2022

Source: Chemical Engineering Journal, Volume 435, Part 1

Author(s): Haibin Chen, Gaowei Yao, Shaopeng Yang, Xuepeng Liu, Molang Cai, Songyuan Dai

In this article, state-of-the-art perovskite solar cells were reported with a small amount of incorporated indium (In³⁺) ions. The In³⁺ ions accumulate at the buried interface and align the energy level to the electron transport layer. Additionally, the charge carrier dynamics at and above the band edge in mixed cation and halide perovskites can be greatly affected.

Abstract

Perovskite solar cells (PSCs) have been propelled into the limelight over the past decade due to the rapid-growing power conversion efficiency (PCE). However, the internal defects and the interfacial energy level mismatch are detrimental to the device performance and stability. In this study, it is demonstrated that a small amount of indium (In³⁺) ions in mixed cation and halide perovskites can effectively passivate the defects, improve the energy-level alignment, and reduce the exciton binding energy. Additionally, it is confirmed that In³⁺ ions can significantly elevate the initial carrier temperature, slow down the hot-carrier cooling rate, and reduce the heat loss before carrier extraction. The device with 1.5% of incorporated In³⁺ achieves a PCE of 22.4% with a negligible hysteresis, which is significantly higher than that of undoped PSCs (20.3%). In addition, the unencapsulated PSCs achieve long-term stability, which retain 85% of the original PCE after 3,000 h of aging in dry air. The obtained results demonstrate and promote the development of practical, highly efficient, and stable hot-carrier-enhanced PSCs.

It is shown that an ammonium chloride additive in precursor solutions governs the even depth distribution of alkali metal (group 1A) elements in methylammonium-free perovskites, favors crystallinity, and induces a lateral growth of large monolithic film grains. Combined with the surface treatment by n-propylammonium iodide, it results in solar cells with high photovoltaic performance and improved stability.

Abstract

Incorporating multiple cations of the 1A alkali metal column of the periodic table (K⁺/Rb⁺/Cs⁺) to prepare perovskite films is promising for boosting photovoltaic properties but requires a uniform distribution. The effects of NH₄Cl additives and alkali metal cations (K⁺/Rb⁺/Cs⁺) on the one-step formation process of methylammonium-free, formamidinium-based, iodide perovskite films are analyzed in a step-by-step manner. NH₄Cl improves the solubility of PbI₂ in solution by forming an intermediate and then favors the perovskite phase formation. Moreover, during the annealing process, this additive is shown to increase grain size, to improve crystallinity and to suppress PbI₂ formation. K at low concentration is always homogeneously distributed across the film thickness. On the other hand, Cs is more concentrated at the surface and Rb in the depths of pristine films. With NH₄Cl additives, these two alkali metals are more homogeneously distributed because NH₄Cl slows down the movement of Cs⁺ and Rb⁺, it changes the growth direction of the perovskite film, making the overall crystallization quality improved and the distribution more uniform. It results in perovskite films with large monolithic grains. Combined with a perovskite film surface treatment with n-propylammonium iodide, a high stabilized power conversion efficiency of 22.04% is reached.

Blade-coating supersaturated CsPb(Br_{1− x} Cl _x )₃ perovskite precursor leads to uniform films with small grains and strong photoluminescence emission. After incorporating the films as an emissive layer in the device, efficient sky-blue perovskite light-emitting diodes (LEDs) with a peak external quantum efficiency reaching 10.3% can be a acheived, along with large-area sky-blue LEDs up to 28 cm² with uniform emission.

Abstract

Large-area fabrication of perovskite light-emitting diodes (PeLEDs) through mass-production techniques has attracted growing attention due to their potential applications in lighting. Several breakthroughs are made for red/infrared and green emissions. Nevertheless, large-area blue/sky-blue PeLEDs, a requisite color for lighting, have not yet been reported. Here, efficient and large-area sky-blue PeLEDs are fabricated through blade-coating supersaturated precursors. The volume ratio of dimethyl sulfoxide to dimethylformamide is tuned to obtain a supersaturated CsPb(Br_0.84Cl_0.16)₃ solution. Blade-coating this supersaturated precursor results in nucleation in the solution phase with much higher nucleation sites, and a faster crystallization rate. The uniform films formed by this approach exhibit smaller grain size, lower trap density, and higher radiative recombination rate. The peak external quantum efficiency of the blade-coated PeLEDs reaches 10.3% with sky-blue emission (489 nm). Benefitting from the robustness of this blade-coating technique, large-area sky-blue PeLEDs with a device area of 28 cm² are also achieved with uniform emission. This work represents a significant step forward toward flat-panel lighting and full-color display for the PeLEDs.

High-efficiency air-fabricated inverted CsPbI₃ PSCs with a wide humidity operating window are realized via an in situ stabilizing strategy. During operation in humidity air, maleic anhydride (MAAD) molecules can convert harmful water erosions into a stabilizer to regulate crystallization and suppress phase transition of CsPbI₃ film. The inverted devices realize champion efficiency of 19.25% with good stability and wide humidity operating window.

Abstract

Inverted triiodine cesium lead (CsPbI₃) perovskite solar cells (PSCs) are promising in photovoltaics owing to their ideal light absorption, non-volatile active layer, and avoidance of fragile Spiro-OmeTAD, especially as the top cell in tandem devices. However, they still exhibit far-lagging efficiency, and must be processed in a strictly controlled environment due to water-fearing CsPbI₃. Here, a novel strategy to convert the harmful water erosions into an in situ stabilizer for efficient inverted CsPbI₃ PSCs fabricated with a wide humidity operating window, is proposed. During air fabrication, maleic anhydride (MAAD) can react with water molecules in air to reduce moisture erosions, while the hydrolysis products (maleic acid, MAAC) control grains growth. After annealing, MAAC strongly binds to CsPbI₃ grains as a shield to hamper phase transition and moisture penetration. A champion efficiency of 19.25% is obtained, which is the highest efficiency among the inverted inorganic PSCs. In parallel, the authors’ optimized devices present efficiency of 18.39% even fabricated in relative humidity 60% condition. Moreover, the stability against various ages is improved, and the optimized devices remain at 96.8% of its initial efficiency after maximum power point tracking at 65 °C for 850 h.

Single-crystal solar cells with high efficiency and a superior weak light response are achieved by engineering the hole extraction interface. Remarkably enhanced efficiency of 22.1% under AM 1.5G irradiation and indoor efficiency of 39.2% under 1000 lux irradiation are obtained, which are both the highest values for MAPbI₃ single-crystal solar cells.

Abstract

Perovskite single crystals have recently been regarded as emerging candidates for photovoltaic application due to their improved optoelectronic properties and stability compared to their polycrystalline counterparts. However, high interface and bulk trap density in micrometer-thick thin single crystals strengthen unfavorable nonradiative recombination, leading to large open-circuit voltage (V _OC) and energy loss. Herein, hydrophobic poly(3-hexylthiophene) (P3HT) molecule is incorporated into a hole transport layer to interact with undercoordinated Pb²⁺ and promote ion diffusion in a confined space, resulting in higher-quality thin single crystals with reduced interface and bulk defect density, suppressed nonradiative recombination, accelerated charge transport, and extraction. As a result, a remarkably enhanced V _OC of up to 1.13 V and efficiency of 22.1% are achieved, which are both the highest values for MAPbI₃ single-crystal solar cells. Moreover, the reduced defect density and suppressed carrier recombination lead to superior weak light response of the single-crystal solar cells after incorporation of P3HT, and an indoor photovoltaic efficiency of 39.2% at 1000 lux irradiation is obtained.

3-sulfopropyl methacrylate potassium salt (SPM) has a multifunctional effect on the crystallization and passivation of perovskite film. The devices passivated by SPM achieve comprehensive efficiency with ≈22% photovoltaic (PV) efficiency and 10.7% electroluminescent (EL) quantum efficiency (under an injection current of short-circuit photocurrent). The reciprocity between PV and EL is correlated.

Abstract

Integration of photovoltaic (PV) and electroluminescent (EL) functions and/or units in one device is attractive for new generation optoelectronic devices but it is challenging to achieve highly comprehensive efficiency. Herein, perovskite solar cells (PSCs) are fabricated, assisted by 3-sulfopropyl methacrylate potassium salt (SPM) additive to tackle this issue. SPMs not only induce large grain size during the film formation but also produce a secondary phase of 2D K₂PbI₄ to passivate the grain boundaries (GBs). In addition, its sulfonic acid group and potassium ion can coordinate to lead ion and fill the interstitial defects, respectively. Thus, SPM reduces the defective states and suppresses nonradiative recombination loss. As a result, planar PSC delivers a power conversion efficiency of ≈22%, with a maximum open-circuit voltage (V _oc) of 1.20 V. The V _oc is 94% of the radiative V _oc limit (1.28 V), higher than the control device (V _oc of 1.12 V). In addition, the reciprocity between PV and EL is also correlated to quantify the energy losses and understand the device physics. When operated as a light-emitting diode, the maximum EL external quantum efficiency (EQE_EL) is up to 12.2% (EQE_EL of 10.7% under an injection current of short-circuit photocurrent), thus leading to high-performance PV/EL dual functions.

A trifluoroethoxyl functionalized hole transport material, Spiro-4TFETAD, is designed and synthesized. Spiro-4TFETAD shows lower highest occupied molecular orbital level, improved hole mobility, conductivity, and hydrophobicity, as well as effectiveness in minimizing perovskite decomposition, compared to Spiro-OMeTAD. Spiro-4TFETAD-based perovskite solar cells exhibit a power conversion efficiency up to 21.11% with excellent stability, which are superior to those of Spiro-OMeTAD-based devices.

It is crucial to finely optimize the properties of hole transport materials (HTMs) to improve the performance and stability of perovskite solar cells (PSCs). Herein, a new spiro-based HTM (Spiro-4TFETAD) is developed by replacement of partial methoxy groups in Spiro-OMeTAD with trifluoroethoxy substituents. Spiro-4TFETAD has lower highest occupied molecular orbital level, higher thermal stability (T _g = 140 °C), hole mobility (2.04 × 10⁻⁴ cm²V⁻¹ s⁻¹), and better hydrophobicity with respect to Spiro-OMeTAD. The PSCs using Spiro-4TFETAD achieve a power conversion efficiency of 21.11% and excellent humidity resistance. It maintains an average 83% of their initial power conversion efficiency values even in high relative humidity of 60% without encapsulation and 82% of its initial performance after 100 h continuous illumination at the maximum power point. The superior performance underscores the promising potential of the trifluoroethoxyl molecular design in preparing new HTMs toward highly efficient and stable PSCs.

A polymeric hole-transport material (HTM) based on the phenanthrocarbazole derivative PC6 features a two-dimensionally conjugated phenanthrocarbazole and S-O noncovalent conformational locking. Perovskite solar cells employing PC6 as a dopant-free HTM afforded an excellent power conversion efficiency (PCE) of 22.2 % and long-term stability.

Abstract

Adequate hole mobility is the prerequisite for dopant-free polymeric hole-transport materials (HTMs). Constraining the configurational variation of polymer chains to afford a rigid and planar backbone can reduce unfavorable reorganization energy and improve hole mobility. Herein, a noncovalent conformational locking via S–O secondary interaction is exploited in a phenanthrocarbazole (PC) based polymeric HTM, PC6, to fix the molecular geometry and significantly reduce reorganization energy. Systematic studies on structurally explicit repeats to targeted polymers reveals that the broad and planar backbone of PC remarkably enhances π–π stacking of adjacent polymers, facilitating intermolecular charge transfer greatly. The inserted “Lewis soft” oxygen atoms passivate the trap sites efficiently at the perovskite/HTM interface and further suppress interfacial recombination. Consequently, a PSC employing PC6 as a dopant-free HTM offers an excellent power conversion efficiency of 22.2 % and significantly improved longevity, rendering it as one of the best PSCs based on dopant-free HTMs.

An extended π-conjugated organic spacer, namely TTDMAI, is successfully developed as spacers for 2D Dion–Jacobson perovskites. A champion efficiency of 18.82% is demonstrated due to the improved film quality and preferred crystal vertical orientation thanks to the templated grain growth by the large crystal nuclei size in the precursor solution.

Abstract

2D Dion–Jacobson (DJ) perovskites have become an emerging photovoltaic material with excellent structure and environmental stability due to their lacking van der Waals gaps relative to 2D Ruddlesden–Popper perovskites. Here, a fused-thiophene-based spacer, namely TTDMAI, is successfully developed for 2D DJ perovskite solar cells. It is found that the DJ perovskite using TTDMA spacer with extended π-conjugation length exhibits high film quality, large crystal size and preferred crystal vertical orientation induced by the large crystal nuclei in precursor solution, resulting in lower trap density, reduced exciton binding energy and oriented charge transport. As a result, the optimized 2D DJ perovskite device based on TTDMA (nominal n = 4) delivers a champion PCE up to 18.82%. Importantly, the unencapsulated device based on TTDMA can sustain average 99% of their original efficiency after being stored in N₂ for 4400 h (over 6 months). Moreover, light, thermal, environmental and operational stabilities are also significantly improved in comparison with their 3D counterparts.

High-quality quasi-2D perovskite/poly(2-ethyl-2-oxazoline) (PEOXA) composite thin films are successfully fabricated with high photoluminescence quantum efficiency via a one-step method. By adjusting the phenylbutanammonium iodide (PBAI) molar ratio and the PEOXA concentration, uniform and smooth perovskite thin films are obtained with high photoluminescence quantum yields and tunable emission from pure red to deep red. With an appropriate content of PBAI spacer and moderate concentration of the polymer additive PEOXA, highly efficient and stable pure-red perovskite light-emitting diodes (PeLEDs) are fabricated. The PeLED exhibits an ultralow turn-on voltage of 1.6 V, maximum luminance of 1942 cd m⁻², maximum EQE of 9.1%, and a record T ₅₀ of 20 h at an initial luminance of 100 cd m⁻².

Abstract

Remarkable progress has been achieved in perovskite light-emitting diodes (PeLEDs) . Both green and infrared PeLEDs with external quantum efficiencies (EQEs) of over 20% are successfully developed. However, the performance of pure red PeLEDs remains challenging. Numerous efforts are explored to tune red color emission for higher emission efficiencies, but it is still suffering operation instability. Here, high-quality and luminescent quasi-2D (CsPbBr _x I_{3 − x} )/poly(2-ethyl-2-oxazoline) (PEOXA) composite perovskite thin films are successfully fabricated via a one-step method. Uniform and smooth perovskite thin films are obtained with photoluminescent quantum yield as high as 65% and emission is tuned from pure red to deep red (638–686 nm). Efficient PeLEDs with device structure of indium tin oxide/ZnMgO/quasi-2D perovskite/Poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)-benzidine] (Poly-TPD)/MoO₃/Ag have demonstrated a high EQE of 7.0% and pure red emission peak at 654 nm, with Commission Internationale de l'Éclairage coordinates of (0.703, 0.287). While the PeLEDs with an emission peak at 670 nm show a low turn-on voltage of 1.6 V, maximum luminance of 1942 cd m⁻², and maximum EQE of 9.1%. In addition, the PeLEDs achieve good spectral and operational stability with a record half-lifetime (T ₅₀) of over 20 h at a high initial luminance of 100 cd m⁻², demonstrating their good potential for display application.

A surface reconstruction strategy is proposed to optimize the surface defect states and crystallization dynamics in an all-inorganic perovskite/organic two-terminal tandem solar cell, leading to efficient hole transport and charge recombination in the interconnecting layer. Finally, a power conversion efficiency of 21.04% and robust operational stability are obtained.

Abstract

The construction of monolithic two-terminal tandem solar cells (2T TSCs) offers the possibility of pursuing high power conversion efficiency (PCE) by overcoming the single-junction Shockley–Queisser limit in photovoltaics. However, little attention is paid to simultaneously improve the stability by utilizing the complementary properties of various photoactive layers. Here, beyond the stacked photoactive layers featuring complementary absorption, all-inorganic perovskite (CsPbI_1.8Br_1.2) is chosen as the photoactive layer of the front wide-bandgap subcell for its intrinsic high thermal stability and ultraviolet (UV)-filtering function to address the burn-in and UV degradation of organic rear subcells. To realize their monolithic integration, the charge recombination efficiency in the interconnecting layer (ICL) between the two types of subcells is tentatively improved by surface reconstruction of all-inorganic perovskite using trimethylammonium chloride. The repaired CsPbI_1.8Br_1.2 surface enables effective suppression of nonradiative recombination and facilitates hole transport, providing efficient charge recombination in the ICL in the 2T TSC. As a result, the all-inorganic perovskite/organic 2T TSC delivers a promising PCE of 21.04%, accompanied by an ultrahigh open-circuit voltage (V _oc) of 2.05 V, which is nearly equal to the superposition of the respective V _oc values of the subcells. More importantly, the 2T TSC simultaneously shows outstanding operational and UV stabilities.

Nature Energy, Published online: 18 October 2021; doi:10.1038/s41560-021-00912-8

Thienothiophene-Based Cation Treatment

In article number 2103130, Selcuk Yerci, Gorkem Gunbas, and co-workers fabricate perovskite solar cells (PSC) by treating 3D perovskite surfaces with a novel cation, which enables higher power conversion efficiency (PCE) and improved stability. The PCE enhancement is explained by drift diffusion modeling. Additionally, treated 3D perovskite based semitransparent PSCs are realized with increased stability and with one of the highest reported efficiencies for double cationic 3D perovskites.

Pure formamidinum (FA)-based 2D perovskite solar cells (PSCs) achieve a record power conversion efficiency (PCE) of 21.07% (certified over 20%), the highest efficiency for low-dimensional PSCs (n ≤ 10) reported to date, together with the improved device stability. The high-efficiency device exhibits a narrowed bandgap and unique 2D–3D intermixing phase distribution for improved light absorption and superior charge transport.

Abstract

Owing to their insufficient light absorption and charge transport, 2D Ruddlesden–Popper (RP) perovskites show relatively low efficiency. In this work, methylammonium (MA), formamidinum (FA), and FA/MA mixed 2D perovskite solar cells (PSCs) are fabricated. Incorporating FA cations extends the absorption range and enhances the light absorption. Optical spectroscopy shows that FA cations substantially increase the portion of 3D-like phase to 2D phases, and X-ray diffraction (XRD) studies reveal that FA-based 2D perovskite possesses an oblique crystal orientation. Nevertheless, the ultrafast interphase charge transfer results in an extremely long carrier-diffusion length (≈1.98 µm). Also, chloride additives effectively suppress the yellow δ-phase formation of pure FA-based 2D PSCs. As a result, both FA/MA mixed and pure FA-based 2D PSCs exhibit a greatly enhanced power conversion efficiency (PCE) over 20%. Specifically, the pure FA-based 2D PSCs achieve a record PCE of 21.07% (certified at 20%), which is the highest efficiency for low-dimensional PSCs (n ≤ 10) reported to date. Importantly, the FA-based 2D PSCs retain 97% of their initial efficiency at 85 °C persistent heating after 1500 h. The results unambiguously demonstrate that pure-FA-based 2D PSCs are promising for achieving comparable efficiency to 3D perovskites, along with a better device stability.

Herein, lead acetate and lead thiocyanate are explored as dual lead sources to prepare high-quality methylammonium lead iodide perovskite films in ambient air through an eco-friendly way, which results in unprecedented efficiency for perovskite solar cells prepared from non-halide lead sources. In addition, the device also shows excellent air stability.

Abstract

The realization of highly efficient perovskite solar cells (PSCs) in ambient air is considered to be advantageous for low-cost commercial manufacturing. However, it is fundamentally difficult to achieve comparable device performance to that obtained in an inert atmosphere, especially when the ambient humidity is high. Here, an effective precursor engineering that simultaneously employs non-halide lead acetate and lead thiocyanate lead sources for fabricating high-quality methylammonium lead iodide perovskite films in ambient air with enhanced moisture tolerance, is reported. The presence of Ac^– and SCN^– ions not only enables the facile formation of homogeneous and highly crystalized perovskite films, but also directs the uniform growth of the crystals along the (110) direction. Accordingly, a 20.55% efficiency is demonstrated, one of the best results for air-processed MAPbI₃ PSCs, which is also the highest value achieved with non-halide lead sources. Furthermore, the unencapsulated device shows fivefold prolonged air stability (3600 h) compared to the conventional PbI₂-based PSC. Together with the use of non-toxic antisolvent, this strategy is fully compatible with ambient air operation and thus of great potential for practical applications.

Herein, by partial substitution of the A-site cation using diethylammonium iodide (DEAI), deeper energy levels are obtained. At the same time, the trap density is reduced, and the grain size is significantly improved. The fabricated solar cell shows much enhanced efficiency from 7.31% to 10.28% with the stability of 50 days maintaining 78%.

Environment-friendly tin perovskite solar cells (T-PKSCs) are the most suitable alternative candidate for lead-free PKSCs. However, the photovoltaic performance of such T-PKSCs is far below those of lead-based perovskite solar cells due to an energetic mismatch between the perovskite layer and charge transport layers. Herein, it is shown that, by partial substitution of the A-site cation using diethylammonium iodide (DEAI) substitution, deeper energy levels are obtained. At the same time, the trap density is reduced and the grain size is significantly improved. The fabricated solar cell shows much enhanced efficiency from 7.31% to 10.28%, short-circuit current density from 18.68 to 21.69 mA cm⁻², open-circuit voltage from 0.59 to 0.67 V, and fill factor from 0.67 to 0.71 after DEAI substitution. Such an efficiency improvement can be explained by matching energy levels at the interfaces between perovskite layer and the charge transport layers. In addition, after 50 days of storage, the modified T-PKSCs demonstrate high stability maintaining 78% of its initial efficiency, whereas the reference device degrades to 68% during 28 days storage.

The surface chemistry of metal halide perovskite quantum dots (PQDs) plays a key role in determining their structural stability and electronic properties. A critical overview focusing on the surface ligand engineering of PQDs, including advanced synthesis, in situ passivation, and ligand exchange, toward efficient and stable optoelectronic applications is presented.

Abstract

The presence of surface ligands not only plays a key role in keeping the colloidal integrity and non-defective surface of metal halide perovskite quantum dots (PQDs), but also serves as a knob to tune their optoelectronic properties for a variety of exciting applications including solar cells and light-emitting diodes. However, these indispensable surface ligands may also deteriorate the stability and key properties of PQDs due to their highly dynamic binding and insulating nature. To address these issues, a number of innovative surface chemistry engineering approaches have been developed in the past few years. Based on an in-depth fundamental understanding of the surface atomistic structure and surface defect formation mechanism in the tiny nanoparticles, a critical overview focusing on the surface chemistry engineering of PQDs including advanced colloidal synthesis, in-situ surface passivation, and solution-phase/solid-state ligand exchange is presented, after which their unprecedented achievements in photovoltaics and other optoelectronics are presented. The practical hurdles and future directions are critically discussed to inspire more rational design of PQD surface chemistry toward practical applications.

Publication date: 17 November 2021

Source: Joule, Volume 5, Issue 11

Author(s): Wenxiao Zhang, Xiaodong Li, Sheng Fu, Xiaoyan Zhao, Xiuxiu Feng, Junfeng Fang