Chen Weijie

Nature, Published online: 08 November 2023; doi:10.1038/s41586-023-06707-z

The effect of in-gap states on recombination rates in quasi-2D lead–iodide-based perovskites, intercalated with various spacer molecules, is studied using a combination of scanning tunneling spectroscopy, temperature-dependent photoconductivity measurements, and theoretical calculations. Tunneling spectra reveal shallow in-gap states that appear to dominate the recombination kinetics of photogenerated carriers in these systems.

In-gap states and their effect on recombination rates in quasi-2D lead–iodide-based perovskites, intercalated with various spacer molecules, are studied using a combination of scanning tunneling spectroscopy and temperature-dependent photoconductivity measurements. The results are further analyzed by a Shockley–Read–Hall model. Indications for shallow in-gap states, positioned at about 0.15–0.2 eV below the bottom of the conduction band, are found. These states are identified as dominating the recombination route of photogenerated carriers in these systems, with a relatively large capture coefficient of about 10⁻⁵–10⁻⁶ cm³ s⁻¹ at room temperature. First-principles calculations based on density functional theory imply that these states are not an intrinsic effect of the inclusion of the spacer molecules, but rather one that arises from chemical defect formation or structural deformation of the perovskite layers. The results suggest that further improvement of the performance of solar cells that are based on quasi-2D perovskites requires, along with enhancing carrier mobility, efforts to suppress the concentration of these detrimental defect states.

The Ga microdroplets are incorporated into conventional carbon electrode to form Ga/C composite electrode. The embedded Ga additive is prone to fill the pores and enhance the electrical conductivity of the composite electrode to facilitate charge carrier transport and collection, as a result, improved device performance of perovskite solar cells.

Carbon electrode-based perovskite solar cells (C-PSCs) exhibit a promising future for commercialization, due to their low cost, facile fabrication, and mass production potential. However, compared with metal-based counter electrodes, carbon electrodes (CEs) often suffer from relatively low electrical conductivity, porous and rough morphology leading to poor interfacial contact with the underneath layer thereby restricting the power conversion efficiency (PCE) of C-PSCs. Herein, a simple approach is presented to prepare liquid metal/carbon composite electrodes by uniformly dispersing liquid gallium droplets into CEs to enhance both the electrical conductivity and interfacial contact between carbon and the adjacent layer. Compared to control devices without Ga, the Ga-embedded carbon also creates a more favorable energy band alignment with the hole transport layer underneath for efficient hole transport, thus suppressing recombination at the interfaces. By optimizing the weight ratio between Ga and the carbon paste, the corresponding C-PSCs deliver an optimum PCE of 13.99% with a higher fill factor (68.95%) compared to pristine C-PSCs (PCE = 13.13%). In addition, the Ga-containing devices demonstrate reinforced thermal stability with 65% efficiency retention after 1800 min under a thermal stress of 80 °C without encapsulation.

A multifunctional molecular bridging layer using 2,5-dichloroterephthalic acid as a pre-buried additive on the tin oxide (SnO₂) electron transport layer enables interfacial energy level alignment and defect passivation. As a result of the method, the high power conversion efficiencies of 23.25% and 20.23% for the active area of 0.15 cm² device and 17.52 cm² mini-module are achieved, respectively.

Abstract

Tin oxide (SnO₂) is currently the dominating electron transport material (ETL) used in state-of-the-art perovskite solar cells (PSCs). However, there are amounts of defects distributed at the interface between ETL and perovskite to deteriorate PSC performance. Herein, a molecule bridging layer is built by incorporating 2,5-dichloroterephthalic acid (DCTPA) into the interface between the SnO₂ and perovskites to achieve better energy level alignment and superior interfacial contact. The multifunctional molecular bridging layer not only can passivate the trap states of Sn dangling bonds and oxygen vacancies resulting in improved conductivity and the electron extraction of SnO₂ but also can regulate the perovskite crystal growth and reduce defect-assisted nonradiative recombination due to its strong interaction with undercoordinated lead ions. As a result, the DCTPA-modified PSCs achieve champion power conversion efficiencies (PCEs) of 23.25% and 20.23% for an active area of 0.15 cm² device and 17.52 cm² mini-module, respectively. Moreover, the perovskite films and PSCs based on DCTPA modification show excellent long-term stability. The unencapsulated target device can maintain over 90% of the initial PCE after 1000 h under ambient air. This strategy guides design methods of molecule bridging layer at the interface between SnO₂ and perovskite to improve the performance of PSCs .

The addition of potassium hypophosphite into perovskite precursor solution regulates crystallization and passivates ionic defects in wide-bandgap (WBG) perovskites. Single-junction WBG devices with a high efficiency of 20.06% retain ≈96% of their initial efficiency after 913 h of continuous AM1.5 G illumination. Meanwhile, monolithic all-perovskite tandem solar cells achieve an efficiency of 26.08%.

Abstract

By integrating wide-bandgap (WBG) and narrow-bandgap perovskites, monolithic all-perovskite tandem solar cells have garnered significant attention as a prospective strategy for surpassing the efficiency limits of single-junction cells. However, the WBG subcells, which significantly impact the performance and operational stability of all-perovskite tandem solar cells, face notable challenges associated with pronounced nonradiative recombination losses and limited film photostability. Here, an efficient method is reported by adding potassium hypophosphite into the perovskite precursor solution to simultaneously regulate crystallization and passivate ionic defects in WBG perovskites. This approach results in high-quality perovskite films and significantly improves the performance and photostability of WBG perovskite solar cells. The single-junction devices with a 1.79 eV bandgap achieve a champion power conversion efficiency (PCE) of 20.06% with an open-circuit voltage of 1.32 V. The devices retain ≈96% of their initial PCE following 913 h of continuous AM 1.5 G illumination. With these WBG perovskite subcells, monolithic all-perovskite tandem solar cells are fabricated with an efficiency of 26.08%.

The external voltage (V _OC) is often significantly smaller than the internal voltage (QFLS), especially in not-yet-optimized devices, which often dominates the voltage loss. Here, various reasons for this discrepancy with real-world examples and strategies to reduce these losses are highlighted. The work also shows that a QFLS-V _OC mismatch occurs during light-soaking and device degradation due to ion accumulation at the interfaces.

Abstract

Perovskite solar cells have demonstrated low non-radiative voltage losses and open-circuit voltages (V _OCs) that often match the internal voltage in the perovskite layer, i.e. the quasi-Femi level splitting (QFLS). However, in many cases, the V _OC differs remarkably from the internal voltage, for example in devices without perfect energy alignment. In terms of recombination losses, this loss often outweighs all non-radiative recombination losses observed in photoluminescence quantum efficiency measurements by many orders of magnitude. As such, understanding this phenomenon is of great importance for further perovskite solar cell development and tackling stability issues. The classical theory developed for Si solar cells explains the QFLS-V _OC mismatch by considering the partial resistances/conductivities for majority and minority carriers. Here, the authors demonstrate that this generic theory applies to a variety of physical mechanisms that give rise to such a mismatch. Additionally, it is found that mobile ions can contribute to a QFLS-V _OC mismatch in realistic perovskite cells, and it is demonstrated that this can explain various key observations about light soaking and aging-induced V _OC losses. The findings in this paper shine a light on well-debated topics in the community, identify a new degradation loss, and highlight important design principles to maximize the V _OC for improved perovskite solar cells.

In this study, a high-quality hole transport layer, IC-CH, is developed by anchoring mixed carbazolyl hole-selective-molecules on optically transparent indium tin oxide nanocrystals films for mixed Pb-Sn NBG PSCs and all-perovskite tandem solar cells. The first evidence of all-perovskite tandem solar cells based on all-SAMs HTL (without PEDOT : PSS) is demonstrated, with efficiency as high as 28.1 %.

Abstract

Combining wide-band gap (WBG) and narrow-band gap (NBG) perovskites with interconnecting layers (ICLs) to construct monolithic all-perovskite tandem solar cell is an effective way to achieve high power conversion efficiency (PCE). However, optical losses from ICLs need to be further reduced to leverage the full potential of all-perovskite tandem solar cells. Here, metal oxide nanocrystal layers anchored with carbazolyl hole-selective-molecules (CHs), which exhibit much lower optical loss, is employed to replace poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT : PSS) as the hole transporting layers (HTLs) in lead-tin (Pb-Sn) perovskite sub-cells and ICLs in all-perovskite tandem solar cells. Optically transparent indium tin oxide nanocrystals (ITO NCs) layers are employed to enhance anchoring of CHs, while a mixture of two CHs is adopted to tune the surface energy-levels of ITO NCs. The optimized mixed Pb-Sn NBG perovskite solar cells demonstrate a high PCE of 23.2 %, with a high short-circuit current density (J _sc) of 33.5 mA cm⁻². A high PCE of 28.1 % is further obtained in all-perovskite tandem solar cells, with the highest J _sc of 16.7 mA cm⁻² to date. Encapsulated tandem solar cells maintain 90 % of their reference point after 500 h of operation at the maximum power point (MPP) under 1-Sun illumination.

A functional passivation material, 1,3-DTu, is added into triple-cation perovskite precursor for the first time for efficient n–i–p planar perovskite solar cells with efficiency exceeding 23% due to the strong interaction between Pb in CFM and S in 1,3-DTu.

Perovskite solar cells (PSCs) have demonstrated immense potential for commercial applications. However, among the factors hindering further improvements in their performance, defects in the perovskite layers during the solution preparation process remain the primary culprit. Here, for the first time, 1,3-dimethylthiourea (1,3-DTu) into triple-cation perovskite layer is introduced, taking advantage of the strong interaction between C=S in 1,3-DTu and Pb in perovskite to significantly improve the quality of the perovskite thin films. This leads to a notable reduction in defects, suppression of nonradiative recombination, and enhancement of the optoelectronic properties of the films. The outcome proves highly positive, with the optimal PSC demonstrating an impressive power conversion efficiency (PCE) exceeding 23%, which is remarkably higher than the control one that yields ≈21%. Additionally, the optimized device exhibits excellent stability, maintaining over 90% and 83% of its initial PCE after 1200 h aging in air with a ≈30% relative humidity at room temperature and after 1700 h of heating at a constant temperature of 85 °C in N₂, respectively, much better than the control one without the incorporation of 1,3-DTu.

A low-cost and high-performance poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine]-based contact for silicon solar cells is reported. After insertion of an ultrathin Al₂O₃ interlayer, which acts as a surface passivating layer, a silicon solar cell with an efficiency of 20.2% is achieved using a simplified fabrication process. Herein, a guiding principle for organic polymer in crystalline silicon solar cells is provided.

Carrier-selective contacts based on inorganic materials (e.g., silicon layers and metal oxides) have been intensively investigated for efficient crystalline silicon (c-Si) photovoltaics. Compared to the vacuum deposition process for inorganic films, organic semiconductors offer a simplified and low-cost processing. Herein, solution-processed poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine] (PTAA) is developed as hole-selective contact for c-Si solar cells. PTAA exhibits a suitable band alignment with p-type c-Si, featuring a small valence band offset (≈0.1 eV) and a large conduction band offset (≈2.2 eV) for effective electron blocking. PTAA combined with Al₂O₃ passivation interlayer is demonstrated to simultaneously offer a low contact resistivity (36.5 mΩ cm²) and a moderate surface passivation (implied open-circuit voltage 635.6 mV) on p-type c-Si surface. By the implementation of a full-area hole-selective Al₂O₃/PTAA rear contact, a champion efficiency of 20.2% is achieved on the hybrid c-Si solar cells. Herein, a guiding principle for future research on polymeric carrier-selective contact for c-Si solar cells is provided.

Additive engineering is widely utilized to optimize film morphology in organic solar cells (OSCs). However, the role of additive in film formation and molecular packing remains unclear at the molecular level. Here, taking Y6-based OSC films as an example, this work employs all-atom molecular-dynamics simulations to investigate how introduction of additives with different π-conjugation degree thermodynamically and dynamically impacts molecular packings.

Abstract

Additive engineering is widely utilized to optimize film morphology in active layers of organic solar cells (OSCs). However, the role of additive in film formation and adjustment of film morphology remains unclear at the molecular level. Here, taking high-efficiency Y6-based OSC films as an example, this work thus employs all-atom molecular-dynamics simulations to investigate how introduction of additives with different π-conjugation degree thermodynamically and dynamically impacts nanoscale molecular packings. These results demonstrate that the van der Waals (vdW) interactions of the Y6 end groups with the studied additives are strongest. The larger the π-conjugation degree of the additive molecules, the stronger the vdW interactions between additive and Y6 molecules. Due to such vdW interactions, the π-conjugated additive molecules insert into the neighboring Y6 molecules, thus opening more space for relaxation of Y6 molecules to trigger more ordered packing. Increasing the interactions between the Y6 end groups and the additive molecules not only accelerates formation of the Y6 ordered packing, but also induces shorter Y6-intermolecular distances. This work reveals the fundamental molecular-level mechanism behind film formation and adjustment of film morphology via additive engineering, providing an insight into molecular design of additives toward optimizing morphologies of organic semiconductor films.

An efficient hybrid and photoconductive electron transportation layer (ETL) by introducing a water/alcohol-soluble fluorescent conversion agent, sodium 2,2’-([1,1'-biphenyl]-4,4'-diyldivinylene)- bis(benzenesulfonate)(CBS), into Zinc Oxide (ZnO) is successfully developed for the non-fullerene organic solar cell (OSC), which produces a higher device power conversion efficiency especially in devices with thicker ETLs and improves the photostability of ZnO:CBS-based OSC devices by reducing the photocatalytic degradation of the non-fullerene electron acceptor.

Abstract

Zinc oxide (ZnO) is widely used as an electron transporting layer (ETL) for organic solar cells (OSCs). Here, a low-cost commercial water/alcohol-soluble fluorescent conversion agent, sodium 2,2′-([1,1′-biphenyl]−4,4′-diyldivinylene)-bis(benzenesulfonate) (CBS), is incorporated into ZnO to develop a novel organic-inorganic hybrid ETL for high-performance OSCs. The photoinduced charge transfer from CBS to ZnO significantly improves the charge transport properties of ZnO, resulting in faster electron extraction and reduced charge recombination in OSC devices with ZnO:CBS ETLs. ZnO:CBS-based devices exhibit higher power conversion efficiencies (PCEs) than their pure ZnO-based counterparts, especially in devices with a thicker ETL, which is more suitable for roll-to-roll and large-area module processing. Furthermore, the strong ultraviolet-light absorption capability of CBS inhibits the photodegradation of the active layer, improving the photostability of ZnO:CBS based OSC devices. Therefore, this work provides a simple and effective strategy for realizing high-performance OSCs with high PCE and good photostability, which can further facilitate the commercialization of OSCs.

Publication date: 20 December 2023

Source: Joule, Volume 7, Issue 12

Author(s): Haoming Liang, Jiangang Feng, Carlos D. Rodríguez-Gallegos, Maximilian Krause, Xi Wang, Ezra Alvianto, Renjun Guo, Haohui Liu, Radha Krishnan Kothandaraman, Romain Carron, Ayodhya N. Tiwari, Ian Marius Peters, Fan Fu, Yi Hou

The intrinsic properties of PEDOT: PSS are regulated by adding molybdenum-containing semiconductors (MoO₃ and MoS₂). The MoO₃-PEDOT: PSS and MoS₂-PEDOT: PSS solutions exhibit lower acidity, while their thin films show improved conductivity and enhanced electron-blocking ability. With the modified PEDOT: PSS layer, organic solar cells composed of PM6:Y6 and PM6:L8-BO achieve champion power conversion efficiencies of 18.0% and 18.9%, respectively.

Abstract

Anode interlayers play critical roles in organic solar cells, impacting the electrode's work function, energy level alignment, hole extraction, and electrode surfaces. However, the development of the commonly used anode interlayer PEDOT:PSS lags behind the rapid development of organic solar cells due to its low conductivity, acidity, and poor electron-blocking capabilities. Herein, an innovative strategy is proposed to regulate the intrinsic properties of PEDOT:PSS by incorporating molybdenum-containing semiconductors (MoO₃, MoS₂), which is validated using the state-of-the-art active layer consisting of PM6:Y6 in conventional devices. The addition of molybdenum-containing semiconductors alters the aggregation morphology of the PEDOT:PSS layer, increasing its conductivity and reducing its acidity. Furthermore, the hole extraction and electron-blocking ability are improved by changing the work function of the anode with the influence of the deep energy level and by forming a trap energy level to capture electrons. Consequently, when the interlayer is employed, a champion power conversion efficiency of 17.1% in the PM6:Y6 devices and 18.9% in organic solar cells composed of PM6:L8-BO is achieved. The results, which enhance the intrinsic properties of PEDOT:PSS with molybdenum-containing semiconductors, offer valuable guidelines for engineering anode interlayers to fabricate highly efficient non-fullerene organic solar cells.

Nature Energy, Published online: 02 November 2023; doi:10.1038/s41560-023-01388-4

SPINBOT, a fully automated platform, integrates machine learning to optimize solution-processed perovskite thin films. It efficiently explores an intricate multi-dimensional parameter space to produce high-quality and reproducible films. As a result, the optimized film achieves an impressive 21.6% power conversion efficiency in solar cells under ambient conditions, along with excellent long-term stability.

Abstract

Simultaneously optimizing the processing parameters of functional thin films remains a challenge. The design and utilization of a fully automated platform called SPINBOT is presented for the engineering of solution-processed functional thin films. The SPINBOT is capable of performing experiments with high sampling variability through the unsupervised processing of hundreds of substrates with exceptional experimental control. Through the iterative optimization process enabled by the Bayesian optimization (BO) algorithm, the SPINBOT explores an intricate parameter space, continuously improving the quality and reproducibility of the produced thin films. This machine learning (ML)-guided reliable SPINBOT platform enables the acceleration of the optimization process of perovskite solar cells via a simple photoluminescence characterization of films. As a result, this study arrives at an optimal film that, when processed into a solar cell in an ambient atmosphere, immediately yields a champion power conversion efficiency (PCE) of 21.6% with satisfactory performance reproducibility. The unsealed devices retain 90% of their initial efficiency after 1100 h of continuous operation at 60–65 °C under metal-halide lamps. It is anticipated that the integration of robotic platforms with the intelligent algorithm will facilitate the widespread adoption of effective autonomous experimentation to address the evolving needs and constraints within the materials science research community.

The acrylamide treatment before perovskite crystallization, and light-induced cross-linking (ABC) strategy can not only passivate defects between grain boundaries but also induce the preferred crystal orientation in polycrystalline perovskite films. Finally, devices fabricated using the proposed strategy show an excellent power conversion efficiency (PCE) of 24.45%, and large-area perovskite solar cell modules show a PCE of 20.31% (33 cm²).

Abstract

Mixed-halide perovskites have emerged as outstanding light absorbers that enable the fabrication of efficient solar cells; however, their instability hinders the commercialization of such systems. Grain-boundary (GB) defects and lattice tensile strain are critical intrinsic-instability factors in polycrystalline perovskite films. In this study, the light-induced cross-linking of acrylamide (Am) monomers with non-crystalline perovskite films is used to fabricate highly efficient and stable perovskite solar cells (PSCs). The Am monomers induce the preferred crystal orientation in the polycrystalline perovskite films, enlarge the perovskite grain size, and cross-link the perovskite grains. Additionally, the liquid properties of Am effectively releases lattice strain during perovskite-film crystallization. The cross-linked interfacial layer functions as an airtight wall that protects the perovskite film from water corrosion. Devices fabricated using the proposed strategy show an excellent power conversion efficiency (PCE) of 24.45% with an open-circuit voltage (V _OC) of 1.199 V, which, to date, is the highest V _OC reported for hybrid PSCs with electron transport layers (ETLs) comprised of TiO₂. Large-area PSC modules fabricated using the proposed strategy show a power conversion efficiency of 20.31% (with a high fill factor of 77.1%) over an active area of 33 cm², with excellent storage stability.

A bifunctional molecule, p-aminobenzoic acid (PABA), increases ion migration barrier, induces (100) facet perovskite grain growth, and yields defect-reduced, homogeneous films. The blade-coated PABA-based inverted PSC achieves an impressive PCE of 23.32% and maintains 93.8% of its initial efficiency after 1000 hours under 1-sun illumination at 75 °C and 10% relative humidity.

Abstract

The fabrication of perovskite solar cells (PSCs) through blade coating is seen as one of the most viable paths toward commercialization. However, relative to the less scalable spin coating method, the blade coating process often results in more defective perovskite films with lower grain uniformity. Ion migration, facilitated by those elevated defect levels, is one of the main triggers of phase segregation and device instability. Here, a bifunctional molecule, p-aminobenzoic acid (PABA), which enhances the barrier to ion migration, induces grain growth along the (100) facet, and promotes the formation of homogeneous perovskite films with fewer defects, is reported. As a result, PSCs with PABA achieved impressive power conversion efficiencies (PCEs) of 23.32% and 22.23% for devices with active areas of 0.1 cm² and 1 cm², respectively. Furthermore, these devices maintain 93.8% of their initial efficiencies after 1 000 h under 1-sun illumination, 75 °C, and 10% relative humidity conditions.

Publication date: 20 December 2023

Source: Joule, Volume 7, Issue 12

Author(s): Yuan Gao, Xinrong Yang, Rui Sun, Lin-Yong Xu, Zeng Chen, Meimei Zhang, Haiming Zhu, Jie Min

Nature, Published online: 01 November 2023; doi:10.1038/s41586-023-06784-0

A new internal degradation mechanism in semi-transparent perovskite solar cells (Indium tin oxide/tin oxide/perovskite/Spiro-MeOTAD/molybdenum trioxide (MoO₃)/transparent conducting oxide) is unraveled. When the hole-transport layer's surface is enriched with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), Li⁺ diffused into MoO₃ layer and results in continuous degradation of the device. Conversion of LiTFSI into stable lithium oxides improves both efficiency and stability of the device due to the effective mitigation of Li⁺ diffusion.

Abstract

Conventional semi-transparent perovskite solar cells (ST-PSCs) generally exhibit inferior performance and stability relative to opaque PSCs. However, a comprehensive understanding of the origins of inferior performance and stability of ST-PSCs and a practical solution to these challenges are both lacking. Here, it is shown for the first time that lithium ions from a lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-doped 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]−9,9′-spirobifluorene (Spiro-MeOTAD) hole-transport layer (HTL) can diffuse into the molybdenum trioxide buffer layer at their interface, yielding ST-PSCs with lower efficiency and accelerated degradation. It is also demonstrated that this undesired Li-ion diffusion can be avoided by HTL surface modification with stable lithium oxides. Using this approach, the constructed ST-PSC exhibits a new record power conversion efficiency (PCE) of 22.02% (21.68% certified) and a fill factor of >80%, with >99% shelf-stability after 400 h and >99% operational stability for 240 h, which clears away this longstanding limitation of the performance and stability of ST-PSCs. This strategy is also applied to fabricate four- and two-terminal perovskite/silicon tandem solar cells with bifacial equivalent efficiencies of 31.5% and 26.34%, respectively, at 20% albedo.

The entangled strategy for manipulating the vertical gradient distribution is proposed to trade-off the efficiency and mechanical properties of flexible organic solar cells. The toughened-pseudo planar heterojunction (Toughened-PPHJ) film exhibits excellent tensile resistance, with twice the crack onset strain of the bulk heterojunction (BHJ) film (11.0%/5.5%). Meanwhile, the efficiency of Toughened-PPHJ device is 18.16%, significantly better than BHJ device (16.99%).

Abstract

Flexible organic solar cells (FOSCs) have attracted considerable attention from researchers as promising portable power sources for wearable electronic devices. However, insufficient power conversion efficiency (PCE), intrinsic stretchability, and mechanical stability of FOSCs remain severe obstacles to their application. Herein, an entangled strategy is proposed for the synergistic optimization of PCE and mechanical properties of FOSCs through green sequential printing combined with polymer-induced spontaneous gradient heterojunction phase separation morphology. Impressively, the toughened-pseudo-planar heterojunction (Toughened-PPHJ) film exhibits excellent tensile properties with a crack onset strain (COS) of 11.0%, twice that of the reference bulk heterojunction (BHJ) film (5.5%), which is among the highest values reported for the state-of-the-art polymer/small molecule-based systems. Finite element simulation of stress distribution during film bending confirms that Toughened-PPHJ film can release residual stress well. Therefore, this optimal device shows a high PCE (18.16%) with enhanced (short-circuit current density) J _SC and suppressed energy loss, which is a significant improvement over the conventional BHJ device (16.99%). Finally, the 1 cm² flexible Toughened-PPHJ device retains more than 92% of its initial PCE (13.3%) after 1000 bending cycles. This work provides a feasible guiding idea for future flexible portable power supplies.

Compared to widely adopted low-dimensional/three-dimensional (LD/3D) heterostructure, functional organic cation based surface termination on perovskite can not only realize advantage of defect passivation but also prevent potential disadvantage of the heterostructure induced intercalation into 3D perovskite. However, it is still very challenging to controllably construct surface termination on organic-inorganic hybrid perovskite because the functional organic cations’ substitution reaction is easy to form LD/3D heterostructure. Here, we report using a novel benzyltrimethylammonium (BTA) functional cation with rational designed steric hindrance to effectively surface terminate onto methylammonium lead triiodide (MAPbI3) perovskite, which is composed of the most unstable MA cations. The BTA cation is difficult to form a specific 1.5-dimensional perovskite of BTA4Pb3I10 by cation substitution with MA cation, which then provides a wide processing window (around 10 minutes) for surface terminating on MAPbI3 films. Moreover, the BTAI surface terminated BTAI-MAPbI3 shows better passivation effect than BTA4Pb3I10-MAPbI3 heterojunction. Finally, BTAI surface terminated solar cell (0.085 cm2) and mini-module (11.52 cm2) obtained the efficiencies of 22.03% and 18.57%, which are among the highest efficiencies for MAPbI3 based ones.

Herein, semitransparent perovskite solar cells (PSCs) with a 10 nm thick active layer are fabricated by controlling the crystallization process during the thermal evaporation of the perovskite layer. The devices show an open-circuit voltage of 1.08 V and a fill factor (FF) of 80%, reaching an efficiency of 3.6% with a high average visible transmittance of 54.2%.

Abstract

Metal halide perovskites are of great interest for application in semitransparent solar cells due to their tunable bandgap and high performance. However, fabricating high-efficiency perovskite semitransparent devices with high average visible transmittance (AVT) is challenging because of their high absorption coefficient. Here, a co-evaporation process is adopted to fabricate ultra-thin CsPbI₃ perovskite films. The smooth surface and orientated crystal growth of the evaporated perovskite films make it possible to achieve 10 nm thin films with compact and continuous morphology without pinholes. When integrated into a p-i-n device structure of glass/ITO/PTAA/perovskite/PCBM/BCP/Al/Ag with an optimized transparent electrode, these ultra-thin layers result in an impressive open-circuit voltage (V_OC) of 1.08 V and a fill factor (FF) of 80%. Consequently, a power conversion efficiency (PCE) of 3.6% with an AVT above 50% is demonstrated, which is the first report for a perovskite device of a 10 nm active layer thickness with high V_OC, FF and AVT. These findings demonstrate that deposition by thermal evaporation makes it possible to form compact ultra-thin perovskite films, which are of great interest for future smart windows, light-emitting diodes, and tandem device applications.

Nature Materials, Published online: 30 October 2023; doi:10.1038/s41563-023-01705-y

Publication date: March 2024

Source: Journal of Energy Chemistry, Volume 90

Author(s): Wenjing Hu, Jian Yang, Chuang Yang, Xufeng Xiao, Chaoyang Wang, Zhaozhen Cui, Qiaojiao Gao, Jianhang Qi, Minghao Xia, Yaqiong Su, Anyi Mei, Hongwei Han