Surface Passivation Of Perovskite Film Research Articles

4-Methoxy phenethylammonium halide salts for surface passivation of perovskite films towards efficient and stable solar cells

Surface defects-mediated non-radiative charge recombination in polycrystalline perovskite films has been widely acknowledged to be responsible for the undesired open-circuit voltage (VOC) deficit, which is still a great challenge for perovskite solar cells (PSCs) to achieve the Shockley-Queisser efficiency limit. Herein, we report the use of 4-methoxy phenethylammonium halide salts (4-MeO-PEAX, X = I, Br, Cl) on the surface of formamidinium-cesium (FACs) perovskite films for surface passivation. The impact of halogen species in 4-MeO-PEAX on the quality of FACs perovskite films and device performance are comparatively investigated. We find that the prepared FACs perovskite films demonstrate dramatically reduced defect density and surface roughness, improved crystallinity, preferred (001) orientation and prolonged carrier lifetime after the post-treatment by 4-MeO-PEACl. Consequently, the 4-MeO-PEACl post-processed p-i-n PSCs have achieved a significantly improved power conversion efficiency of 22.63 % and VOC of 1.13 V. The unencapsulated devices post-treated with 4-MeO-PEACl maintained 90 %, 88 % and 84 % of their initial efficiencies, after being thermally stressed at 65 ℃ under dark for 312 h, stored in ambient air for 720 h and operated under continuous 1 sun equivalent illumination with maximum power point tracking at 50 ℃ for 1000 h, respectively.

Reducing the Surface Reactivity of Alkyl Ammonium Passivation Molecules Enables Highly Efficient Perovskite Solar Cells

AbstractThe non‐radiative recombination at the interfaces of perovskite solar cells (PSCs) is a crucial issue that limits the efficiency and stability of the devices. State‐of‐the‐art surface passivation strategies usually utilize alkyl ammonium halides to suppress the non‐radiative recombination of PSCs, but their high surface reactivity leads to the transformation into 2D perovskites under working conditions, limiting the passivation effect and the charge transport of PSCs. Herein, a non‐halide ionic salt 1‐naphthylmethylammonium formate (NMACOOH) is synthesized for surface passivation of perovskite films. In contrast to the traditional 1‐naphthylmethylammonium iodide, NMACOOH treatment hinders the formation of 2D perovskite and forms a thermally stable PbI2‐NMACOOH adduct on the perovskite surface. Surface characterization reveals that NMA+ can passivate the cation vacancies of the 3D perovskite while HCOO− passivates the metallic Pb0 and halide‐vacancy defects. Therefore, the non‐radiative recombination of PSCs is dramatically suppressed and a high open‐circuit voltage of 1.19 V is obtained. Finally, PSCs with high efficiency of 24.75% and improved long‐term stability (98% of the initial efficiency after 1800‐h storage) are obtained. Moreover, the NMACOOH‐passivated devices also show robust operational stability, retaining 83% of the initial efficiency after working for 658 h under continuous one‐sun illumination.

Enhanced performance of MAPbI2.85Br0.15 perovskite solar cells via ionic liquid-induced surface passivation of perovskite films

Metal halide perovskite solar cells are considered as a competitive new force for next-generation photovoltaic, whereas the interfacial defect of perovskite films severely degrades the performance and stability of the devices. Herein, we introduce the 1-ethyl-3-methylimidazolium acetate ([EMIM]Ac) ionic liquid to passivate lead-related defect on the surface of the MAPbI2.85Br0.15 perovskite films. The carbonyl groups of [EMIM]Ac coordinate with the uncoordinated lead ions on the perovskite surface, and meanwhile the [EMIM]Ac ionic liquid suppresses the formation of metallic lead, which effectively reduces the nonradiative recombination and improves the working stability. As a result, the power conversion efficiency of the solar cell with [EMIM]Ac treatment is improved from 16.95 % to 19.29 %. The unencapsulated device shows good stability and retains the initial efficiency of 95 % after being exposed in ambient environment for 240 h. Therefore, this ionic liquid surface passivation proposed in this work may shed light on the development and practical application of perovskite solar cells.

Ethylenediamine Vapors‐Assisted Surface Passivation of Perovskite Films for Efficient Inverted Solar Cells

Defects present at the surface or within the bulk of halide perovskites act as a barrier to charge transfer/transport, induce nonradiative recombination thereby limit open‐circuit voltage (VOC), and accelerate degradation in the perovskite solar cells (PSCs). Passivation of these defects at surfaces, interfaces, and grain boundaries to suppress the charge recombination is therefore imperative to improving photovoltaic performance in the PSCs. Herein, a facile posttreatment of perovskite surface by ethylenediamine (EDA) via mixed solvent vapor annealing method is reported. The results show that only a trace amount of EDA causes significant suppression of nonradiative recombination leading to over 100 mV increased VOC and ≈22% improvement in power conversion efficiency (PCE) of the inverted PSCs. The key reasons for this improvement are an upward shift in the Fermi energy level, reduced lattice strain and Urbach energy, and reduction in nonradiative recombination upon EDA passivation. These lead to a PCE exceeding 20% up from 16% for a nonpassivated film. The unencapsulated EDA‐modified PSCs also demonstrate an improved shelf‐life and retain 87% of the initial PCE after 850 h.

Effect of functional groups in passivating materials on stability and performance of perovskite solar cells

Functional groups (ammonium versus amidinium and aryl versus alkyl) of passivating materials play a critical role in the surface passivation of perovskite films.

Surface passivation of perovskite films by potassium bis(fluorosulfonyl)imide for efficient solar cells

Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted much attention because of their high photoelectric conversion efficiency (PCE) and simple preparation process. At present, one of the major factors limiting the further improvement of PSCs’ performance is defects in perovskite active layers. Herein, we report an effective surface post-treatment method for perovskite active layers, which uses potassium bis(fluorosulfonyl)imide (KFSI) to passivate multiple defects, improve photovoltaic performance and reduce the hysteresis. It is demonstrated that not only S=O and S–N bonds but also charged K + and FSI − ions in KFSI contribute to the passivation of multiple defects in perovskite films via Lewis acid-base interaction and/or forming ionic bonds. After the optimized KFSI treatment, the trap density of the perovskite film decreased from 8.41 × 10 15 cm −3 to 3.97 × 10 15 cm −3 , which significantly suppressed trap-assisted nonradiative recombination of carriers in perovskite films and/or at perovskite/hole transport layer interface. The KFSI treated device achieved a PCE of ∼19.00% with less hysteresis, appreciably outperforming the control device (17.22%). At the same time, the performance reproducibility among the fabricated solar cells was remarkably improved. This work provides a facile way to passivate multiple defects in perovskite films and further enhance the performance of perovskite solar cells. • An effective passivator - potassium bis(fluorosulfonyl)imide (KFSI) for passivating multiple perovskite defects is reported. • Not only S=O and S–N bonds but also charged K + and FSI − ions in KFSI contribute to the passivation of multiple defects. • After the optimized KFSI treatment, the trap density decreased, which suppressed non-radiative recombination of carriers. • The KFSI treated device appreciably outperforms the control device in terms of efficiency, hysteresis and reproducibility.

Improving the stability and efficiency of inorganic CsPbI2Br perovskite via surface reconstruction strategy

Inorganic CsPbX3 (X = Cl, Br, I) perovskite without volatile organic components in crystal lattice, has outstanding thermal stability and broad application prospects. Various strategies have been adopted to restrain the notorious phase transition process (from cubic to orthorhombic phase) for high photoelectric conversion efficiency (PCE). Nevertheless, most studies simply focus on the surface passivation of perovskite films, ignoring the influence of surface element segregation, which is inevitable during perovskite crystallization and growth process. Herein, 2-thiopheneacetic acid (2-TPAA) was adopted to reconstruct the surface of CsPbI2Br film via secondary growth process. The constituent elements of CsPbI2Br especially Br- enrich on the surface under the action of 2-TPAA. Meanwhile, the carboxyl and thiophene groups of 2-TPAA bidentate anchor Pb2+ ions respectively, forming protective layer to inhibit the invasion of external factors. In addition, the film morphology, moisture resistance, thermodynamic stability as well as carrier transport performance of perovskite films also get improved significantly. The black phase of CsPbI2Br survives in air ambient for several days, via the synergism of surface reconstruction and passivation effect. Furthermore, the device PCE increased to 15.03%, and retained 90% initial PCE during 400 d aging. The surface reconstruction strategy provides a convenient method to improve the phase stability of CsPbI2Br perovskite films in air ambient.

Quasi‐2D Bilayer Surface Passivation for High Efficiency Narrow Bandgap Perovskite Solar Cells

AbstractThe combination of comprehensive surface passivation and effective interface carriers transfer plays a critical role in high‐performance perovskite solar cells. A 2D structure is an important approach for surface passivation of perovskite film, however, its large band gap could compromise carrier transfer. Herein, we synthesize a new molecule 2‐thiopheneethylamine thiocyanate (TEASCN) for the construction of bilayer quasi‐2D structure precisely on a tin‐lead mixed perovskite surface. This bilayer structure can passivate the perovskite surface and ensure effective carriers transfer simultaneously. As a result, the open‐circuit voltage (Voc) of the device is increased without sacrificing short‐circuit current density (Jsc), giving rise to a high certified efficiency from a credible third‐party certification of narrow band gap perovskite solar cells. Furthermore, theoretical simulation indicates that the inclusion of TEASCN makes the bilayer structure thermodynamically more stable, which provides a strategy to tailor the number of layers of quasi‐2D perovskite structures.

Quasi-2D Bilayer Surface Passivation for High Efficiency Narrow Bandgap Perovskite Solar Cells.

The combination of comprehensive surface passivation and effective interface carriers transfer plays a critical role in high-performance perovskite solar cells. A 2D structure is an important approach for surface passivation of perovskite film, however, its large band gap could compromise carrier transfer. Herein, we synthesize a new molecule 2-thiopheneethylamine thiocyanate (TEASCN) for the construction of bilayer quasi-2D structure precisely on a tin-lead mixed perovskite surface. This bilayer structure can passivate the perovskite surface and ensure effective carriers transfer simultaneously. As a result, the open-circuit voltage (Voc ) of the device is increased without sacrificing short-circuit current density (Jsc ), giving rise to a high certified efficiency from a credible third-party certification of narrow band gap perovskite solar cells. Furthermore, theoretical simulation indicates that the inclusion of TEASCN makes the bilayer structure thermodynamically more stable, which provides a strategy to tailor the number of layers of quasi-2D perovskite structures.

Synergy of mesoporous SnO2 and RbF modification for high-efficiency and stable perovskite solar cells

Electron transport layer (ETL) is very critical to the performance of perovskite solar cells (PSCs), and optimization work on ETL has received extensive attentions especially on tin oxide (SnO2) since it is an excellent ETL material widely applied in high-efficiency PSCs. Thereinto, introducing mesoporous structure and surface modification are two important approaches which are commonly applied. Herein, based on the previous work in low-temperature fabrication process of mesoporous SnO2 (m-SnO2), we introduced a modification process with rubidium fluoride (RbF) to the m-SnO2 ETL, and successfully achieved a synergy of the m-SnO2 and RbF modification: not only the shortcoming of the m-SnO2 in interfacial traps was overcome, but also the carrier collection efficiency was further improved. The PSCs based on the m-SnO2 ETL with RbF modification demonstrated outstanding performances: a champion power conversion efficiency (PCE) of 22.72% and a stability performance of maintaining 90% of the initial PCE after 300 h of MPP tracking were obtained without surface passivation of perovskite film. Hence, utilizing the abovementioned synergy is a cost-effective and feasible strategy for fabricating high-efficiency and stable PSCs since the fabrication process of the m-SnO2 ETL is a kind of low temperature process and RbF is cheap.

Revealing phase evolution mechanism for stabilizing formamidinium-based lead halide perovskites by a key intermediate phase

Revealing phase evolution mechanism for stabilizing formamidinium-based lead halide perovskites by a key intermediate phase

Decoupling the effects of defects on efficiency and stability through phosphonates in stable halide perovskite solar cells

Summary Understanding defects is of paramount importance for the development of stable halide perovskite solar cells (PSCs). However, isolating their distinctive effects on device efficiency and stability is currently a challenge. We report that adding the organic molecule 3-phosphonopropionic acid (H3pp) to the halide perovskite results in unchanged overall optoelectronic performance while having a tremendous effect on device stability. We obtained PSCs with ∼21% efficiency that retain ∼100% of the initial efficiency after 1,000 h at the maximum power point under simulated AM1.5G illumination. The strong interaction between the perovskite and the H3pp molecule through two types of hydrogen bonds (H…I and O…H) leads to shallow point defect passivation that has a significant effect on device stability but not on the non-radiative recombination and device efficiency. We expect that our work will have important implications for the current understanding and advancement of operational PSCs.

Small grains as recombination hot spots in perovskite solar cells

Summary Non-radiative recombination in the perovskite bulk and at its interfaces prohibits the photovoltaic performance from reaching the Shockley-Queisser limit. While interfacial recombination has been widely discussed and demonstrated, bulk recombination and especially the influence of grain boundaries remain under debate. Most studies explore the role of grain boundaries on perovskite films rather than devices, making it difficult to link the film properties with those of the devices. Here, we systematically investigate the effects of grain boundaries on the performance of perovskite solar cells by two different methods. By combining experimental characterization with theoretical device simulations, we find that the recombination at grain boundaries is diffusion limited and hence is inversely proportional to the grain area to the power of 3/2. Consequently, the prevalence of small grains—which act as recombination hot spots—across the perovskite active layer dictates the photovoltaic performance of the perovskite solar cells.

Lead-free tin perovskite solar cells

Summary The development of efficient and stable lead-free perovskite solar cells (PSCs) is crucial for addressing the concern of environmental pollution from the toxic element lead. In recent years, tin PSCs have emerged as a promising candidate for high-performance, eco-friendly photovoltaic technology with a high certified power conversion efficiency (PCE) of more than 11%, indicating a great potential for future applications. Here, we review the recent efficiency progress of tin PSCs based on the equivalent circuit model of solar cells. We then discuss approaches toward efficiency improvement from the device viewpoint, such as optimizing the band gap, increasing the light-harvesting efficiency and carrier diffusion length, surface passivation, and regulating the interface energy-level alignment. Finally, we point out the possibility of reaching 20% PCE for tin PSCs and issues regarding enlarging the cell size and realizing scalable production in the future. We expect that these perspectives will be helpful for accelerating the commercialization of tin PSCs.

A Porphyrin-Involved Benzene-1,3,5-Tricarboxamide Dendrimer (Por-BTA) as a Multifunctional Interface Material for Efficient and Stable Perovskite Solar Cells.

Surface defects of perovskite films are the major sources of nonradiative recombination which limit the efficiency and stability of perovskite solar cells. Surface passivation represents one of the most efficient strategies to solve this problem. Herein, for the first time we designed a porphyrin-involved benzene-1,3,5-tricarboxamide dendrimer (Por-BTA) as a multifunctional interface material between the interface of the perovskite and the hole-transporting layer (spiro-OMeTAD) for the surface passivation of perovskite films. The results suggested that Por-BTA not only efficiently passivated the perovskite surface defects via the coordination of the exposed Pb2+ with the carbonyl unit and basic sites of pyrrole units in Por-BTA but also improved the interface contact and the charge transfer between the perovskite and spiro-OMeTAD ascribed to the strong intermolecular π-π stacking of Por-BTA. It was shown that the PSC devices with the Por-BTA treatment exhibited improved power conversion efficiency with the champion of 22.30% achieved (21.30% for the control devices), which is mainly attributed to the increased short-circuit current density and fill factor. Interestingly, the stability of moisture for the Por-BTA-treated device was also enhanced compared to those without the Por-BTA treatment. This work presents a promising direction toward the design of multifunctional organic molecules as the interface materials to improve the cell performance of PSCs.

Defect-passivation of organometal trihalide perovskite with functionalized organic small molecule for enhanced device performance and stability

Defects in solution-processed organic and inorganic halide perovskite thin films deteriorate their photovoltaic performance and stability. Here, a bisimidazole-based organic small molecular hole transport material (HTM) that can suppress interfacial defects of the perovskite with its functional groups working as Lewis bases is newly introduced. Surface passivation of perovskite film leads to the reduction in non-radiative recombination trap density as well as the improvement of its crystallinity, consequently enhancing the efficiency of perovskite solar cell (PSC) from 16.3% to 18.3% with superior stability, preserving 92% of its initial efficiency for 500 h in an atmosphere.

Behind the Breakthrough of the ∼30% Perovskite Solar Cell

In the December 11, 2020 issue of Science, Al-Ashouri and colleagues reported a certified monolithic perovskite/silicon tandem solar cell with the power conversion efficiency 29.15%. The improvements of the ideality factor and the fill factor are key to achieving efficient perovskite tandem solar cells, which lead a new direction of the perovskite research.

High-performance methylammonium-free ideal-band-gap perovskite solar cells

Summary The development of mixed tin-lead (Sn-Pb)-based perovskite solar cells (PSCs) with low band gap (1.2–1.4 eV) has become critical not only for pushing single-junction devices toward the maximum efficiency given by the Shockley-Queisser limit, but also for enabling all-perovskite tandem devices beyond this limit. However, achieving high power-conversion efficiency (PCE) and long-term device operation stability simultaneously remains a significant challenge for Sn-Pb-based PSCs. Here, we demonstrate near ideal-band-gap (∼1.34 eV) methylammonium-free Sn-Pb-based PSCs with high efficiency (∼20%) and promising operational stability of maintaining >80% of initial PCE over 750 h under maximum-power-point tracking. The key to this success is the use of a SnCl2⋅3FACl complex additive that improves the microstructure and reduces the development of residual stress in the Sn-Pb perovskite thin films, which in turn enhances the efficiency and stability of the Sn-Pb-based ideal-band-gap PSCs.

Direct Surface Passivation of Perovskite Film by 4-Fluorophenethylammonium Iodide toward Stable and Efficient Perovskite Solar Cells.

Passivating the defective surface of perovskite films is becoming a particularly effective approach to further boost the efficiency and stability of their solar cells. Organic ammonium halide salts are extensively utilized as passivation agents in the form of their corresponding 2D perovskites to construct the 2D/3D perovskite bilayer architecture for superior device performance; however, this bilayer device partly suffers from the postannealing-induced destructiveness to the 3D perovskite bulk and charge transport barrier induced by the quantum confinement existing in the 2D perovskite. Hence, developing direct passivation of the perovskite layer by organic ammonium halides for high-performance devices can well address the above-mentioned issues, which has rarely been explored. Herein, an effective passivation strategy is proposed to directly modify the perovskite surface with an organic halide salt 4-fluorophenethylammonium iodide (F-PEAI) without further postannealing. The F-PEAI passivation largely inhibits the formation of the iodine vacancies and thus dramatically reduces the film defects, resulting in a much slower charge trapping process. Consequently, the F-PEAI-modified device achieves a much higher champion efficiency (21%) than that (19.5%) of the control device, which dominantly results from more efficient suppression of interfacial nonradiative recombination and the subsequent decreased recombination losses. Additionally, the F-PEAI-treated device maintains 90% of its initial efficiency after 720 h of humidity aging owing to the enhanced hydrophobicity and decreased trap states, highlighting good ambient stability. These results provide an effective passivation strategy toward efficient and stable perovskite solar cells.

Efficient surface passivation of perovskite films by a post-treatment method with a minimal dose

Post-treatement of an unannealed perovskite film is found to be more efficienct way to passivate defects of perovskite solar cells.