Stable Planar Perovskite Solar Cells Research Articles

Enhanced optoelectronic characteristics of La-doped ZnO and its compatibility with Cs-doped MAPbI3 perovskite absorber material

Abstract The present study investigates the structural, electrical and optical characteristics of pristine and lanthanum (La)-doped zinc oxide electron transport layers (ETLs) fabricated by the sol gel method and their compatibility with Cs0.10MA0.90Pb(I0.9Br0.10)3 absorber layer for perovskite solar cells. All the ETLs were deposited under same deposition conditions, with the only difference in La percentage in the precursor solutions, ranging from 0 to 6%. X-ray diffraction (XRD) analysis demonstrated the presence of crystalline ZnO thin films and the absence of any impurity phases after La-doping. The calculated crystallite size, determined using Scherrer’s equation, increased from 11.13 to 21.76 nm after the introduction of dopant. The doping with 4% La led to the decrease in the optical bandgap from 3.32 eV of pristine ZnO to 3.23 eV. SEM analysis revealed better morphology of perovskite/4% La:ZnO specimen, which facilitated the absorbance and reduced the charge carrier recombination. It also exhibited superior resilience towards moisture and humidity which will eventually contribute to the development of more stable and efficient planar perovskite solar cells (PCSs).

Tuning Pyrrolo[3,2-b] pyrrole Core-based hole transport materials properties via Addition of fluorine for highly efficient and Stable planar perovskite solar cells

Hole-transport materials (HTM) play a crucial role in functioning perovskite solar cells (PSCs). In this research, we develop and synthesize two pyrrolo[3,2-b] pyrrole core (PP) based small molecular HTMs, FPPY and BPPY with/without (w/wo) fluorine (F) substitution on PP core that connected to the carbazole diphenylamine peripheral end groups, respectively. The F-substituted fused electron-rich pyrrole ring core greatly impacts FPPY molecular surface charge distribution, which contributes to higher hole extraction properties and excellent band alignment. Finally, FPPY-based PSCs obtain a best power conversion efficiency (PCE) of 24.3 %, significantly higher than BPPY (20.1 %). After aging 2000 h at ambient condition (25 °C, 30–50 % RH), the FPPY-based device still keeps over 87 % of its initial PCE.

Bifacial perovskite/silicon heterojunction tandem solar cells based on FAPbI3-based perovskite via hybrid evaporation-spin coating

Combining the two technologies of tandem solar cells and bifacial solar cells has a great potential to maximize energy harvesting while minimizing material and surface usage. Mid-bandgap perovskites (1.50–1.60 eV) are important for fulfilling current matching in bifacial perovskite/silicon heterojunction tandem solar cells. Herein, efficient (>20 %) and stable planar FAPbI3-based perovskite (1.54 eV) solar cells have been fabricated via a hybrid evaporation-spin coating process. X-ray diffraction and electron microscopy data reveal the formation of highly crystalline (001) perovskite domains. The fabricated high-quality perovskite films lead to a more homogenized contact potential difference at the film surface and a reduction in non-radiative losses, resulting in a quasi-Fermi-level splitting (half-cell) of 1.16 eV, rendering 120 mV non-radiative losses. Transferring these films into tandem devices atop single-side textured silicon heterojunction bottom cells, we obtain an efficiency of >24 % under AM1.5 G illumination for monofacial devices with an active area of 1.21 cm2. Furthermore, the bifacial devices generate >27 mW cm−2 power output with 15 % rear illumination fraction.

Multifunctional buried interface engineering via phenyl-phosphonic acid for efficient and stable SnO2-based planar perovskite solar cells

Tin dioxide (SnO2) is widely used as an electron transport layer (ETL) in efficient and stable perovskite solar cells (PSCs) due to its excellent optoelectronic properties and low-temperature solution preparation process. However, SnO2 ETLs fabricated by the conventional solution method have many defects, among which Sn dangling bonds (i.e., oxygen vacancies) are particularly prominent. Herein, a simple buried interface engineering is employed to introduce phenyl-phosphinic acid (PPA) into the surface of SnO2 film for the preparation of highly efficient PSCs. A series of test results have shown that the phosphate group (PO) in PPA can not only passivate oxygen vacancy defects on the surface of SnO2, but also improve the film-forming quality of the upper perovskite, thereby exhibiting better photoelectric conversion efficiency (PCE) and stability. Ultimately, the optimized device achieves a maximum PCE of 22.81 %, an improvement of about 15 % over the control device (19.82 %). Meanwhile, the nonencapsulated device based on SnO2-PPA ETL shows much better storage and light stability than the control SnO2.

Multifunctional Polymer Restraint of the Agglomeration of SnO2 Nanocrystals for Efficient and Stable Planar Perovskite Solar Cells.

The aggregation of SnO2 nanocrystals due to van der Waals interactions is not conducive to the realization of a compact and pinhole-free electron transport layer (ETL). Herein, we have utilized potassium alginate (PA) to self-assemble SnO2 nanocrystals, forming a PA-SnO2 ETL for perovskite solar cells (PSCs). Through density functional theory (DFT) calculations, PA can be effectively absorbed onto the surface of SnO2. This inhibits the agglomeration of SnO2 nanocrystals in solution, forming a smoother pinhole-free film. This also changes the surface contact potential (CPD) of the SnO2 film, which leads to a reduction in the energy barrier between the ETL and the perovskite layers, promotes effective charge transfer, and reduces trap density. Consequently, the power conversion efficiency (PCE) of PSCs with a PA-SnO2 ETL increased from 19.24% to 22.16%, and the short-circuit current (JSC) was enhanced from 23.52 to 25.21 mA cm-2. Furthermore, the PA-modified unpackaged device demonstrates better humidity stability compared to the original device.

Interface Modification Using Li-Doped Hollow Titania Nanospheres for High-Performance Planar Perovskite Solar Cells.

Titania nanospheres have been utilized as building blocks of electron transporting layers (ETLs) for mesoscopic perovskite solar cells (PSCs). Nevertheless, the power conversion efficiencies (PCEs) reported so far for the mesoscopic PSCs containing titania nanospheres are generally lower than those of the state-of-the-art planar PSCs. Here, we have prepared Li-doped hollow titania nanospheres (Li-HTS) through a "cation-exchange" approach and used them for the first time to modify the SnO2 ETL/perovskite interfaces of planar PSCs. The Li-HTS-modified PSC delivered a PCE of 23.28% with a fill factor (FF) of over 80%, which is significantly higher than the PCE of the control device (20.51%). This is the best PCE achieved for PSCs containing titania nanospheres. Moreover, interfacial modification using Li-HTS greatly improves the stability of the PSCs. This work demonstrates the potential of interface modification using inorganic nanostructures for enhancing the efficiency and stability of planar PSCs.

Design of fullerene-based interface passivation coatings for n-i-p perovskite solar cells: Addend size matters!

Perovskite solar cells (PSCs) have gained much attention because of their impressive power conversion efficiency (PCE) of up to 25.5%. Currently, low-temperature-processed SnO2 thin films are widely used as the ETLs to achieve efficient and stable planar PSCs. Surface passivation of SnO2 as electron transport layer (ETL) by fullerene derivatives is known as one of the ways to enhance the performance of n–i–p devices. Herein, we report a synthesis of new fullerene derivatives with hydroxyl and carboxyl functional groups, which are expected to contribute to more efficient modification of SnO2 surface. A comparative study of five fullerene derivatives as passivation layers allowed to establish the correlation between the molecular formula and performance of PSCs. Moreover, optimized passivation interlayers of monocyclopropanated fullerene derivative with carboxylic group improved the efficiency of perovskite solar cells in compare with conventional PCBA from 17.0% to 19.5%. This study highlights the key role of molecular design in passivation of SnO2 for pursuing high performance PSCs with n-i-p configuration.

SnO2:TiO2 hybrid nanocrystals as electron transport layer for high-efficiency and stable planar perovskite solar cells

SnO2:TiO2 hybrid nanocrystals as electron transport layer for high-efficiency and stable planar perovskite solar cells

Preparation of Zn2+ doped NiCo2O4: Hole transport layer for high performance of perovskite solar cells

Inorganic hole transport materials (HTMs) play an important role for the stability and efficiency of planar perovskite solar cells (PSCs). Among the numerous inorganic HTMs, NiCo2O4 with its excellent performance is the emerging candidate for hole transport layers (HTLs) and is attracting increasing attention. However, the low electrical conductivity and optical transmittance of NiCo2O4 severely limit the device performance. Herein, the Zn2+ was used to dope NiCo2O4 to improve the electrical conductivity and optical transmittance of NiCo2O4. And the effects of the concentration of Zn2+ on the morphology, structure and properties of NiCo2O4 were investigated. The morphology and transparency of ZnxNi1-xCo2O4 would not be affected when the concentration of Zn2+ is below 0.1, but when it is up to 0.15 and 0.2, the morphology of NiCo2O4 clustered together or showed a diamond-shaped block, and the optical transmittance also decreased significantly. Meanwhile, with the increase of doping amount, the conductivity and hole mobility are gradually increased. As a result, the optimal concentration of Zn2+ is 0.1. Besides, the Zn0.1Ni0.9Co2O4 possessed a significant improvement in hole extraction and better band alignment compared to the NiCo2O4. And hence, the power conversion efficiency (PCE) of PSCs fabricated in open air is up to 13.41% by using Zn0.1Ni0.9Co2O4. This work develops a potential strategy for developing highly efficient and stable PSCs, opens up a new horizon for the development of inorganic HTMs.

Multifunctional Aminoglycoside Antibiotics Modified SnO2 Enabling High Efficiency and Mechanical Stability Perovskite Solar Cells

AbstractSnO2 as an electron transport layer (ETL) has been widely used in regular planar perovskite solar cells (PSCs) owing to its high optical transmittance, less photocatalytic activity, and low‐temperature processing. However, SnO2‐based PSCs still face many challenges which greatly impair their efficiency and stability of PSCs. Herein, a novel and effective multifunctional modification strategy is proposed by incorporating streptomycin sulfate (STRS) molecules with multiple functional groups into SnO2 ETL. STRS can significantly suppress SnO2 nanoparticle agglomeration, improve the electronic property of SnO2, as well as reduce nonradiative recombination. At the same time, interfacial residual tensile stress is released and the interfacial energy level alignment becomes more matched. As a result, the STRS‐modified PSCs achieve a higher efficiency of 22.89% compared to 20.61% of the control device and exhibit a hysteresis‐free feature. The humidity and thermal stability of PSCs based on STRS‐SnO2 are significantly improved. Furthermore, the efficiency of flexible devices increased from 19.74% to 20.79%, and the devices still maintain >80% of initial PCE after 4500 bending cycles with a bend radius of 5 mm. This study provides a low‐cost, facile, and efficient strategy for achieving high efficiency and stability in PSCs.

A facile surface trap passivation of perovskite absorber enabled by tetrabenzocorrolazine dye for efficient and stable planar perovskite solar cells

The trap-site passivation of perovskite absorbers is very important for reducing charge recombination and resultant energy loss in high-performance perovskite solar cells (PSCs). To achieve the successful role of a passivating agent, an appropriate molecular design strategy with specific functional groups should be considered for effective passivation of the defective antisites on the surface of perovskite absorber layers. Here, we designed a tetrabenzocorrolazine phosphorus dye (RC1), that is capable of electron-donating properties with a hydroxyl functionalization, as a multi-functional passivation agent for high-performance PSCs. It is found that the surface properties of the perovskite absorber were stabilized as RC1 interacts with Pb2+ and Cs + cations of the perovskite lattice, providing much improved optoelectronic properties and their charge extraction/collection capability. Moreover, the RC1-passivation successfully reduced carrier recombination and internal energy loss, leading to hysteresis-free power conversion efficiency of 18.922% (14.466% for the control device). The RC1 also retains long-term stability for 2000 h with only 10% efficiency loss of the fresh device. Thus, this study demonstrates a successful passivating capability of functionalized tetrabenzocorrolazine phosphorus dye for high-performance PSCs.

Dual-interface modification strategy via tautomeric UV absorber for efficient and UV stable planar perovskite solar cells

Dual-interface modification strategy via tautomeric UV absorber for efficient and UV stable planar perovskite solar cells

Carbon Electrode with Sputtered Au Coating for Efficient and Stable Perovskite Solar Cells

Halide perovskite solar cells (PSCs) represent a low-cost and high-efficiency solar technology. However, most of the highly efficient PSCs need a noble electrode, such as Au, through thermal evaporation. It is reported that a sputtered Au electrode on a PSC could damage the organic hole transport layer (HTL) and the perovskite layer. Here, we report a simple, yet effective sputtered gold nanoparticle decorated carbon electrode to fabricate efficient and stable planar PSCs. The sputtered Au layer on the doctor-bladed coated carbon electrode can be directly applied to the perovskite semicells by mechanical stacking. By optimizing the gold thickness, a power conversion efficiency (PCE) of 16.87% was obtained for the composite electrode-based PSC, while the reference device recorded a PCE of 12.38%. The composite electrode-based device demonstrated 96% performance retention after being stored under humid conditions (50-60%) without encapsulation for ∼100 h. This demonstrates a promising pathway toward the commercialization of large-scale manufacturable sputtered electrodes for the PSC solar module.

Buried Interface Regulation by Bio-Functional Molecules for Efficient and Stable Planar Perovskite Solar Cells.

Among the factors that lead to the reduction of the efficiency of perovskite solar cells (PSCs) the difficulty involved in realizing a high-quality film and the efficient charge transfer that takes place at the interface between electron-transport layer (ETL) and perovskite is worth mentioning. Here, a strategy for planar-type devices by natural bio-functional interfaces that uses a buried electron-transport layer made of cobalamin complexed tin oxide (SnO2 @B12 ) is demonstrated. Having systematically investigated the effects of SnO2 @B12 interfacial layer in perovskite solar cells, it can be concluded that cobalamin can chemically link the SnO2 layer and the perovskite layer, resulting in improved perovskite film quality and interfacial defect passivation. Utilizing SnO2 @B12 improves the efficiency of planar-type PSCs by 20.60 %. Furthermore, after 250 h of exposure to an ambient atmosphere, unsealed PSCs containing SnO2 @B12 degrade by 10 %. This research provides a viable method for developing bio-functional molecules that will increase the effectiveness and durability of planar-perovskite solar cells.

Simultaneous bottom-up double-layer synergistic engineering by multifunctional natural molecules for efficient and stable SnO2-based planar perovskite solar cells

The performance and stability of perovskite solar cells (PSCs) is limited by detrimental defects, mostly distributed at the grain boundary (GB) of bulk perovskite film and interface, which induce serious carrier non-radiative recombination. Therefore, there is particularly urgent to realize simultaneous passivation of bulk defects and interfacial defects. In this work, a simple, low-cost and effective multifunctional modification strategy is developed by introducing the λ-Carrageenan (λ-C) as the interfacial layer of SnO2/perovskite. The sulfate groups of λ-C not only play a positive role in passivating the Sn4+ from SnO2 film, resulting in high conductivity, but also effectively passivate the defects at the SnO2/perovskite interface. Meanwhile, λ-C can effectively passivate the defects in the perovskite film due to the strong binding force between the high content of sulfate groups and PbI2. The synergistic effect of λ-C simultaneously achieves interfacial defects and bulk defects passivation, better crystalline quality, suppressed charge recombination, released interfacial stress and more favorable interfacial energy level alignment. Based on the above efficient synergy, the λ-C-modified device achieves a high efficiency of 23.81%, which is ∼24.53% higher than the control device (19.12%). To our best knowledge, 23.81% of power conversion efficiency (PCE) is the highest reported PCE value of PSCs employing green natural additives. Moreover, long-term and thermal stabilities are significantly improved after interface modification. Thus, this work provides an idea for developing multifunctional natural materials towards the attainment of the efficient and stable PSCs.

Multiple Function Synchronous Optimization by PbS Quantum Dots for Highly Stable Planar Perovskite Solar Cells with Efficiency Exceeding 23%

AbstractColloidal lead sulfide (PbS) quantum dots (QDs), which possess quantum confinement effect and processing compatibility with perovskite, are regarded as an excellent material for optimizing perovskite solar cells (PSCs). However, the existing PSCs optimized by PbS QDs are still facing the challenges of poor performance of the charge transport layers, low utilization in the near‐infrared (NIR) region, and unsuitable energy level alignment, which limit the improvement of power conversion efficiency (PCE). Herein, a synchronous optimization strategy is realized via simultaneously introducing PbS QDs into SnO2 electron transport layer and employing rare‐earth‐doped PbS QDs (Eu:PbS QDs) film with hydrophobic chain ligands as the NIR light‐absorping layer and hole transport layer (HTL) of devices. PbS QDs effectively decrease the density of trap states by passivating defects. Eu:PbS QDs film with adjustable bandgap is employed as an absorption layer to broaden the NIR spectral absorption. The well‐matched energy level between Eu:PbS QDs layer and perovskite layer implies efficient hole transfer at the interface. The successful synchronous optimization greatly elevates all photovoltaic parameters, reaching a maximum PCE of 23.27%. This PCE is the highest for PSCs utilizing PbS QDs material in recent years. The optimized PSCs retain long‐term moisture and light stability.

Fabrication of a Highly Functional TiO2/AZO Bilayer Electron Transport Layer for Planar Perovskite Solar Cells

A highly functional electron transport layer (ETL) is essential for fabricating stable and efficient perovskite solar cells (PvSCs). Among the various n-type materials, mesoporous titanium dioxide (m-TiO2) is the most widely used ETL in combination with a compact layer. Despite contributing to good efficiency devices, low electron mobility, and a high annealing temperature (>450 °C) to form a crystalline film in the anatase phase, the use of m-TiO2 is a bottleneck for perovskite technology. Aluminum-doped zinc oxide (AZO) is a potential replacement for m-TiO2 as an ETL due to its relatively high electron mobility, high transparency, and low-temperature processing. Here, we demonstrate a low-temperature solution-processed TiO2/AZO bilayer thin film as ETL in a planar PvSCs configuration, which exhibits a power conversion efficiency of 13.94% with a JSC of 19.49 mA/cm2, a VOC of 1.05V, and a FF of 68% with a pixel area of 0.25 cm2. The unencapsulated TiO2/AZO-ETL-based PvSCs retained 70% of their initial efficiency after 1000 h in an ambient atmosphere. Our studies demonstrated that the solution-processed TiO2/AZO bilayer ETLs provide a promising approach for developing low-temperature, high-performance, and stable planar PvSCs.

Interface passivation using choline acetate for efficient and stable planar perovskite solar cells

The choline acetate (ChAc) passivation improves both the device performance and long-term stability.

Thermally Evaporated ZnSe for Efficient and Stable Regular/Inverted Perovskite Solar Cells by Enhanced Electron Extraction

Electron transport layers (ETLs) are crucial for achieving efficient and stable planar perovskite solar cells (PSCs). Reports on versatile inorganic ETLs using a simple film fabrication method and applicability for both low‐cost planar regular and inverted PSCs with excellent efficiencies (>22%) and high stability are very limited. Herein, we employ a novel inorganic ZnSe as ETL for both regular and inverted PSCs to improve the efficiency and stability using a simple thermal evaporation method. The TiO2‐ZnSe‐FAPbI3 heterojunction could be formed, resulting in an improved charge collection and a decreased carrier recombination further proved through theoretical calculations. The optimized regular PSCs based on TiO2/ZnSe have achieved 23.25% efficiency with negligible hysteresis. In addition, the ZnSe ETL can also effectively replace the unstable bathocuproine (BCP) in inverted PSCs. Consequently, the ZnSe‐based inverted device realizes a champion efficiency of 22.54%. Moreover, the regular device comprising the TiO2/ZnSe layers retains 92% of its initial PCE after 10:00 h under 1 Sun continuous illumination and the inverted device comprising the C60/ZnSe layers maintains over 85% of its initial PCE at 85 °C for 10:00 h. This highlights one of the best results among universal ETLs in both regular and inverted perovskite photovoltaics.

High efficiency stable planar perovskite solar cells via heavy water additive

Although great advances have been made in low-cost manufacturing of air-processed perovskite solar cells (PSCs), the moisture degradation of halide perovskite films remains a key problem to be urgently solved. High-quality perovskite films with large grains and uniform coverage are essential to enhance the performance of PSCs with high efficiency and moisture stability. Herein, heavy water (D2O) is employed as an additive in PbI2 precursor to manipulate the average grain size and enhance surface coverage of perovskite film, resulting in improved humidity stability of PSCs under ambient conditions. It is found that the introduction of D2O effectively improves the quality of perovskite film and significantly reduces the grain boundaries for reduced carrier recombination. The optimal concentration of D2O can boost the in-plane growth of perovskite films and increase the average grain size of perovskite from 494 nm to 717 nm. Consequently, the PSCs based on the perovskite film with 1% D2O exhibits a superior PCE of 21.66% (0.055 cm2) in small area, which is 9.78% higher than that of the control device (19.73%). In addition, the large-area (1 cm2) PSCs with 1% D2O show an efficiency of 20.02%. The unencapsulated PSCs made with 1% D2O can remain 95% of its initial PCE after aging 60 days in ambient air under dark with 20–25% relative humidity.