awn

Publication date: November 2020

Source: Nano Energy, Volume 77

Author(s): You-Hyun Seo, Jun Hee Kim, Do-Hyung Kim, Hee-Suk Chung, Seok-In Na

Publication date: November 2020

Source: Nano Energy, Volume 77

Author(s): Qiyao Guo, Jihuai Wu, Yuqian Yang, Xuping Liu, Weihai Sun, Yuelin Wei, Zhang Lan, Jianming Lin, Miaoliang Huang, Hongwei Chen, Yunfang Huang

Publication date: November 2020

Source: Nano Energy, Volume 77

Author(s): Yuying Wu, Wenbin Fan, Zhangran Gao, Zheng Tang, Lin Lei, Xiaofan Sun, Yongle Li, Hong-Ling Cai, Xiaoshan Wu

Publication date: November 2020

Source: Nano Energy, Volume 77

Author(s): Hailiang Wang, Huicong Liu, Weiping Li, Liqun Zhu, Haining Chen

Publication date: October 2020

Source: Nano Energy, Volume 76

Author(s): Savas Sonmezoglu, Seckin Akin

Publication date: November 2020

Source: Nano Energy, Volume 77

Author(s): Ahra Yi, Sangmin Chae, Sejeong Won, Hyun-June Jung, In Hwa Cho, Jae-Hyun Kim, Hyo Jung Kim

Publication date: November 2020

Source: Nano Energy, Volume 77

Author(s): Hyeseung Jung, A-Ra Jung, Seon-Mi Jin, Seah Kim, Hyojung Heo, Hoai Van T. Nguyen, Min Je Kim, Pyeongkang Ahn, Myung Hwa Kim, Youngu Lee, Kyung-Koo Lee, Jeong Ho Cho, Eunji Lee, BongSoo Kim

The mechanism for binary solvent additives to enhance photovoltaic device performance via advanced technology characterizations is unveiled. The binary additives improve polymer order, maintain high crystallinity, and obtain the preferable morphology of photoactive films. As a result, new binary additives result in an enhanced short circuit current and fill factor, and the device performance is improved from 9.11% to 10.64%.

Binary solvent additive engineering is an effective strategy to optimize photoactive films for high‐efficiency organic solar cells, however, the effect of single components on device performance and the combination principle of binary solvent additives remain unclear. Herein, synchrotron‐based grazing incident X‐ray diffraction, Derjaguin–Muller–Toporov modulus imaging, and plasmon energy shift imaging acquired by scanning transmission electron microscopy to investigate the effect of new binary solvent additive of 1,8‐diiodooctane (DIO) and less‐toxic and p‐anisaldehyde (AA) on device performance of solar cells based on poly[(5,6‐difluoro‐2,1,3‐benzothiadiazol‐4,7‐diyl)‐alt‐(3,3‴‐di(2‐octyldodecyl)2,2′;5′,2″;5″,2‴‐quaterthio‐phen‐5,5‴‐diyl)] (PffBT4T‐2OD) and [6,6]‐phenyl‐C61‐butyric acid methyl ester (PC61BM) are used. It is found that AA mainly favors polymer order and high crystallinity of PffBT4T‐2OD. Differently, DIO mainly enables PC61BM diffusing into PffBT4T‐2OD polymer matrix, leading to enlarged donor–acceptor (D–A) interface. As expected, by combining AA and DIO, the composite film provides large D–A interface and more balanced charge carrier transport. Consequently, their beneficial synergistic effect results in enhanced short circuit current and fill factor, and thereby increased power conversion efficiency of 10.64%, improved by 16% with respect to the control device. Herein, a general mechanism of enhancing device performance via the combination of solvent additives with different contributions to photoactive film is unveiled.

Atom‐thick 2D WS₂ nanosheets’ electron‐transport layers (ETLs) facilitate enhanced coupling with the perovskite absorber layer, promoting a highly active interfacial charge transfer dynamic. The single‐crystalline nature of the WS₂ ETL also provides the facile transportation of photogenerated electrons to the electrode for a high‐performance and high‐stability perovskite solar cell.

The structure and the electronic properties of the electron‐transport layer (ETL) of perovskite solar cells (PSCs) govern the interfacial charge transfer and charge transportation to the electrode. The ETLs of two dimensions, that are atom thick, and have a planar structure that possesses special electronic properties, such as the surface collective motion of excitons or charge transfer–driven defect state relief, that is 2D transition metal dichalcogenide, allow a highly energetic carrier dynamic process for enhanced photovoltaic effect. Herein, it is discovered that planar, few‐atom‐thick 2H–WS₂ nanosheets' ETLs drive ultrafast charge transfer and transportation along the ETL during the photovoltaic process. Time‐resolved photoluminescence and electrochemical impedance spectroscopy analysis results indicate that the charge transfer from the perovskite to the ETL occurs as fast as 5.9 ns with charge transfer resistance as low as 25.6 Ω. This allows the PSC device to produce a power conversion efficiency of 18.21% with short‐circuit current density, open‐circuit voltage, and fill factor as high as 22.24 mA cm², 1.12 V, and 0.731, respectively. The PSC retains 96.87% of its performance when being aged in nitrogen atmosphere for 33 days. Atom‐thick planar WS₂ ETL nanosheets can be the basis for the development of high‐performance PSC devices.

Pb and Pb‐free perovskite absorbers are analyzed using a 1D simulator for n‐i‐p devices. SCAPS‐1D simulations suggest: 1) theoretically determined efficiency limit of Cs₂PtI₆ perovskites is comparable with (FA,MA,Cs)Pb(I,Br)₃, 2) FA₄GeSbCl₁₂ is a promising photoabsorber; and 3) for efficient photoconversion with Sn‐, Ge‐, Ti‐, or Ag‐based perovskite absorbers, reduction in defect density and increase in absorption coefficient is needed.

Optoelectronic properties of organic–inorganic halide perovskites are exceptional with solar cells showing efficiency comparable with conventional photovoltaic technologies. However, with issues of material stability and toxicity of Pb, it is important to understand if Pb can be replaced while maintaining the high power conversion efficiencies of (FA,MA,Cs)Pb(I,Br)₃. Herein, practical efficiency limits of Pb and Pb‐free perovskite absorbers are analyzed using a 1D simulator for n‐i‐p or p‐i‐n device structures. SCAPS‐1D baseline models for perovskite absorber materials with and without Pb are developed to numerically reproduce the experimental current density–voltage (JV) and external quantum efficiency (EQE) of champion devices from literature. From these baseline models, the efficiency limits are determined based on optimizing the interface band alignments, reduction in midgap defect density, increased absorption coefficient, and no parasitic losses. SCAPS‐1D simulations suggest that 1) theoretically determined efficiency limit of Cs₂PtI₆ perovskites is comparable with (FA,MA,Cs)Pb(I,Br)₃ perovskites, 2) FA₄GeSbCl₁₂ is a promising photoabsorber; and 3) for efficient photoconversion with Sn‐, Ge‐, Ti‐, or Ag‐based compounds, a reduction of defect density and increase in absorption coefficient is needed.

A recast strategy is proposed to optimize the spatial distribution of components in organic bulk‐heterojunction (BHJ) films in an all‐inorganic perovskite/BHJ integrated solar cells, leading to extended photoresponse, enhanced ambipolar charge transport, and suppressed charge carrier recombination. A record power conversion efficiency of 11.08% and robust thermal stability are obtained.

Abstract

All‐inorganic CsPbIBr₂ perovskite solar cells (pero‐SCs) exhibit excellent overall stability, but their power conversion efficiencies (PCEs) are greatly limited by their wide bandgaps. Integrated solar cells (ISCs) are considered to be an emergent technology that could extend their photoresponse by directly stacking two distinct photoactive layers with complementary bandgaps. However, rising photocurrents always sacrifice other photovoltaic parameters, thereby leading to an unsatisfactory PCE. Here, a recast strategy is proposed to optimize the spatial distribution components of low‐bandgap organic bulk‐heterojunction (BHJ) film, and is combined with an all‐inorganic perovskite to construct perovskite/BHJ ISCs. With this strategy, the integrated perovskite/BHJ film with a top‐enriched donor‐material spatial distribution is shown to effectively improve ambipolar charge transport behavior and suppress charge carrier recombination. For the first time, the ISC is not only significantly extended and enhanced the photoresponse achieving a 20% increase in current density, but also exhibits a high open‐circuit voltage and fill factor at the same time. As a result, a record PCE of 11.08% based on CsPbIBr₂ pero‐SCs is realized; it simultaneously shows excellent long‐term stability against heat and ultraviolet light.

Three homologous small molecule donors with hydrogen, fluorine, and chlorine substitution afford organic solar cells with efficiencies over 10% in combination with a common acceptor. The chlorinated derivative exhibits a more crystalline nanomorphology with relatively pure domains and provides more than 12% efficiency.

Abstract

Compared to conjugated polymers, small‐molecule organic semiconductors present negligible batch‐to‐batch variations, but presently provide comparatively low power conversion efficiencies (PCEs) in small‐molecular organic solar cells (SM‐OSCs), mainly due to suboptimal nanomorphology. Achieving precise control of the nanomorphology remains challenging. Here, two new small‐molecular donors H13 and H14, created by fluorine and chlorine substitution of the original donor molecule H11, are presented that exhibit a similar or higher degree of crystallinity/aggregation and improved open‐circuit voltage with IDIC‐4F as acceptor. Due to kinetic and thermodynamic reasons, H13‐based blend films possess relatively unfavorable molecular packing and morphology. In contrast, annealed H14‐based blends exhibit favorable characteristics, i.e., the highest degree of aggregation with the smallest paracrystalline π–π distortions and a nanomorphology with relatively pure domains, all of which enable generating and collecting charges more efficiently. As a result, blends with H13 give a similar PCE (10.3%) as those made with H11 (10.4%), while annealed H14‐based SM‐OSCs have a significantly higher PCE (12.1%). Presently this represents the highest efficiency for SM‐OSCs using IDIC‐4F as acceptor. The results demonstrate that precise control of phase separation can be achieved by fine‐tuning the molecular structure and film formation conditions, improving PCE and providing guidance for morphology design.

A robust strategy for constructing flexible perovskite solar cells that can be conveniently biodegraded is introduced. The results signify the great potential of meniscus‐assisted solution printing for controllably assembling aligned conductive nanomaterials for biodegradable electrodes. As such, it represents an important endeavor toward environmentally friendly, multifunctional, and flexible electronics.

Abstract

Increasing performance demand associated with the short lifetime of consumer electronics has triggered fast growth in electronic waste, leading to serious ecological challenges worldwide. Herein, a robust strategy for judiciously constructing flexible perovskite solar cells (PSCs) that can be conveniently biodegraded is reported. The key to this strategy is to capitalize on meniscus‐assisted solution printing (MASP) as a facile means of yielding cross‐aligned silver nanowires in one‐step, which are subsequently impregnated in a biodegradable elastomeric polyester. Intriguingly, the as‐crafted hybrid biodegradable electrode greatly constrains the solvent evaporation of the perovskite precursor solution, thereby generating fewer nuclei and in turn resulting in the deposition of a large‐grained dense perovskite film that exhibits excellent optoelectronic properties with a power conversion efficiency of 17.51% in PSCs. More importantly, the hybrid biodegradable electrode‐based devices also manifest impressive robustness against mechanical deformation and can be thoroughly biodegraded after use. These results signify the great potential of MASP for controllably assembling aligned conductive nanomaterials for biodegradable electrodes. As such, it represents an important endeavor toward environmentally friendly, multifunctional and flexible electronic, optoelectronic, photonic, and sensory materials and devices.

A block copolymer is incorporated between the hole transporting layer (HTL) and the photo‐active layer (PAL) of an organic solar cell resulting in the improved stability and efficiency of the device. This is due to the block copolymer preventing long‐term reaction mechanisms between the PAL and the HTL and providing a more energetically favourable energy level for hole transport.

Abstract

In a proof‐of‐concept study, this work demonstrates that incorporating a specifically designed block copolymer as an interfacial layer between a charge transport layer and the photoactive layer in organic solar cells can enhance the interface between these layers leading to both performance and stability improvements of the device. This is achieved by incorporating a P3HT₅₀‐b‐PSS_x block copolymer as an interfacial layer between the hole transporting and photoactive layers, which results in the improvement of the interfacial roughness, energy level alignment, and stability between these layers. Specifically, the incorporation of a 10 nm P3HT₅₀‐b‐PSS₁₆ and a 13 nm P3HT₅₀‐b‐PSS₂₃ interfacial layer results in a 9% and a 12% increase in device efficiency respectively compared to the reference devices. In addition to having a higher initial efficiency, the devices with the block copolymer continue to have a higher normalized efficiency than the control devices after 2200 h of storage, demonstrating that the block copolymer not only improves device efficiency, but crucially, prevents degradation by stabilizing the interface between the hole transporting layer and the photoactive layer. This study proves that appropriately designed and optimized block copolymers can simultaneously stabilize and improve the efficiency of organic solar cells.

A non‐annealed, ultrathin, amorphous metal oxyhydroxide was introduced to suppress interfacial charge recombination and reduce energy loss in electron‐transport‐layer (ETL)‐free perovskite solar cells. The cells achieve a record efficiency of 21.1 %, outperforming their ETL‐containing metal oxide counterparts (18.7 %).

Abstract

The performances of electron‐transport‐layer (ETL)‐free perovskite solar cells (PSCs) are still inferior to ETL‐containing devices. This is mainly due to severe interfacial charge recombination occurring at the transparent conducting oxide (TCO)/perovskite interface, where the photo‐injected electrons in the TCO can travel back to recombine with holes in the perovskite layer. Herein, we demonstrate for the first time that a non‐annealed, insulating, amorphous metal oxyhydroxide, atomic‐scale thin interlayer (ca. 3 nm) between the TCO and perovskite facilitates electron tunneling and suppresses the interfacial charge recombination. This largely reduced the interfacial charge recombination loss and achieved a record efficiency of 21.1 % for n‐i‐p structured ETL‐free PSCs, outperforming their ETL‐containing metal oxide counterparts (18.7 %), as well as narrowing the efficiency gap with high‐efficiency PSCs employing highly crystalline TiO₂ ETLs.

A homochiral molecular ferroelectric was incorporated into a perovskite film to enlarge the built‐in electric field of the perovskite solar cell (PSC), thereby facilitating charge separation and transportation. The molecular ferroelectric component of the PSC passivates the defects in the perovskite active layers to induce an approximately eightfold enhancement in photoluminescence intensity and a reduction in electron trap‐state density.

Abstract

The nonradiative recombination of electrons and holes has been identified as the main cause of energy loss in hybrid organic–inorganic perovskite solar cells (PSCs). Sufficient built‐in field and defect passivation can facilitate effective separation of electron–hole pairs to address the crucial issues. For the first time, we introduce a homochiral molecular ferroelectric into a PSC to enlarge the built‐in electric field of the perovskite film, thereby facilitating effective charge separation and transportation. As a consequence of similarities in ionic structure, the molecular ferroelectric component of the PSC passivates the defects in the active perovskite layers, thereby inducing an approximately eightfold enhancement in photoluminescence intensity and reducing electron trap‐state density. The photovoltaic molecular ferroelectric PSCs achieve a power conversion efficiency as high as 21.78 %.

A novel strategy of tuning perovskite crystal orientation toward ≈45° inclination with respect to the substrate is proposed with incorporating 2,3‐diaminopropionic acid monohydrochloride (2,3‐DAPAC) into FASnI₃, which facilitates charge transport in the perovskite film from bottom to top. The solar cells with 2,3‐DAPAC acquire a champion power conversion efficiency of 7.23% and improved stability.

Despite a higher power conversion efficiency (PCE) than other lead‐free perovskite solar cells (PSCs) due to intrinsically excellent optoelectronic properties and suitable bandgaps of tin (Sn) perovskites, Sn‐based PSCs still suffer from issues of stability and efficiency for practical applications. Herein, a novel strategy of tuning perovskite crystal orientation toward ≈45° with respect to the substrate by doping 2,3‐diaminopropionic acid monohydrochloride (2,3‐DAPAC) into formamidinium tin iodide (FASnI₃) is proposed, which facilitates charge transport in the perovskite film and consequent device performances. In addition, the incorporation of 2,3‐DAPAC into FASnI₃ enables dense and smooth high‐quality perovskite films with less Sn vacancies. Applications of the 2,3‐DAPAC‐treated FASnI₃ films into PSCs acquire a champion PCE of 7.23%, showing 37.2% enhancement compared with 5.27% of the control device. Moreover, the storage stabilities of both perovskite films and PSCs are significantly prolonged with improved film quality.

Passivation is like a pair of magic hands, which can heal defective perovskite cubes to a perfect light absorption layer. Herein, the origin of various defects as well as their detrimental effects on perovskite solar cells (PSCs) performance and the targeted passivation strategies for specific defects are summarized. Finally, the future development trend on passivation is provided.

With a certificated record efficiency of 25.2%, organometal halide perovskite (OHP) solar cells have experienced unprecedentedly rapid development in the past decade due to their extraordinary photoelectronic properties. However, because of the rapid processing conditions and complex precursor compositions, there are a large number of defects in polycrystalline OHP films, including point defects and 2D defects along grain boundary and on the surface. Unfortunately, these defects serve as the nonradiative recombination centers and exert negative effects on the degradation and performance of OHP layers, heavily limiting their further application for efficient photovoltaic devices. Herein, the formation origin of various defects as well as their detrimental effects on the efficiency and stability of perovskite solar cells (PSCs) are discussed, and recent passivation strategies for specific defects to minimize defect state density in the perovskite films are summarized. Finally, a brief outlook on the development trend of future passivation engineering is provided for deeper understanding of efficient and stable PSCs.

A new fluorinated organic ammonium halide salt, 4‐trifluoromethyl phenethylammonium iodide (CFPEAI), is utilized to passivate the surface of CsPbI₂Br perovskite for solar cells with enhanced efficiency as well as improved stability.

Surface modification is demonstrated as an efficient strategy to enhance the efficiency and stability of perovskite solar cells (PVSCs). Fluorinated organic ammonium salts featuring a strong hydrophobic nature are seldom used as passivation agents for the surface modification of CsPbI₂Br perovskites. Herein, a fluorinated organic ammonium halide salt, 4‐trifluoromethyl phenethylammonium iodide (CFPEAI), is incorporated into the surface of CsPbI₂Br perovskite for the first time. After the CFPEAI modification, the defects of CsPbI₂Br perovskite are significantly passivated with reduced trap densities. The best‐performance PVSC with CFPEAI modification shows an excellent power conversion efficiency (PCE) of 16.07% with a high fill factor (FF) of 84.65%, a short‐circuit current density (J _SC) of 15.45 mA cm⁻², and an open‐circuit voltage (V _OC) of 1.23 V. In contrast, the control PVSCs without the surface modification exhibit a lower PCE of 14.50% with a FF of 80.56%, a J _SC of 15.05 mA cm⁻², and a V _OC of 1.20 V. With CFPEAI passivation, the CsPbI₂Br perovskite film exhibits enhanced hydrophobicity, thereby leading to improved stability for the corresponding PVSC in comparison with the control PVSC without any surface modification.

A zwitterionic conjugated polyelectrolyte presents high hole mobility, compatible covalence level, and the ability for passivating surface defects of the perovskite film. The formation of a weak double‐layer capacitance, which is not strong enough to induce the migration of MA⁺ ions, contributes to low carrier transport resistance and interfacial charge accumulation, leading to high efficiency and stability.

Achieving rapid extraction and equivalent transport of charge carriers is an effective way to improve the performance of perovskite solar cells (PSCs). Herein, a thiophene‐based zwitterionic conjugated polyelectrolyte (poly(5‐amino‐5‐carboxy‐3‐oxapentyl)‐2,5‐thiophene [POWT]) is introduced into PSCs as a hole‐transporting and interfacial material. The polyelectrolyte has a high hole mobility of 5.74 × 10⁻³ cm² V⁻¹ s⁻¹ (similar to that of poly(triarylamine) [PTAA]) and compatible covalence level relative to the perovskite. Terminated with a zwitterionic pair of a‐amino acid, POWT layer builds up a weak double‐layer capacitance at the interface, which is not strong enough to induce the migration of MA⁺ ions in the perovskite layer. Deep electrical study on the PSC with the structure of indium tin oxide (ITO)/POWT/FA_0.2MA_0.8PbI_2.9Br_0.1/C₆₀/bathocuproine (BCP)/Ag discloses that the device has low carrier transfer resistance, low leakage current density, and minor interfacial charge accumulation. The open‐circuit voltage and the short‐circuit current density are much improved, and the power conversion efficiency (PCE) is up to 17.5%. With a‐amino acid zwitterions, POWT passivates the surface charge defects and grain boundaries of the perovskite film. The PSC presents negligible hysteresis and high stability. After 56 days, the unencapsulated PSC still remains at 85% of the original efficiency.

Publication date: 16 September 2020

Source: Joule, Volume 4, Issue 9

Author(s): Yihua Chen, Shunquan Tan, Nengxu Li, Bolong Huang, Xiuxiu Niu, Liang Li, Mingzi Sun, Yu Zhang, Xiao Zhang, Cheng Zhu, Ning Yang, Huachao Zai, Yiliang Wu, Sai Ma, Yang Bai, Qi Chen, Fei Xiao, Kangwen Sun, Huanping Zhou

In article number https://doi.org/10.1002/aenm.2020007722000772, Siva Krishna Karuturi, Heping Shen and co‐workers report a perovskite/Si dual absorber tandem cell for stand‐alone solar water splitting. An unprecedented over 17% solar‐to hydrogen conversion efficiency is achieved when a Si photocathode is paired in tandem with a high bandgap (≈1.75 eV) semitransparent perovskite solar cell.

Barriers with compact morphology/structure and shielding capability can be designed/ integrated in perovskite solar cells to prevent issues like product volatilization, ion diffusion, electrode corrosion, and ingress of the harmful components brought about by the intrinsic interface failure or the attack of heat, sunlight, electric bias, and H₂O/O₂, leading to robust stability of the whole device.

Abstract

Perovskite solar cells (PSCs) have attracted much attention in the past decade and their power conversion efficiency has been rapidly increasing to 25.2%, which is comparable with commercialized solar cells. Currently, the long‐term stability of PSCs remains as a major bottleneck impeding their future commercial applications. Beyond strengthening the perovskite layer itself and developing robust external device encapsulation/packaging technology, integration of effective barriers into PSCs has been recognized to be of equal importance to improve the whole device’s long‐term stability. These barriers can not only shield the critical perovskite layer and other functional layers from external detrimental factors such as heat, light, and H₂O/O₂, but also prevent the undesired ion/molecular diffusion/volatilization from perovskite. In addition, some delicate barrier designs can simultaneously improve the efficiency and stability. In this review article, the research progress on barrier designs in PSCs for improving their long‐term stability is reviewed in terms of the barrier functions, locations in PSCs, and material characteristics. Regarding specific barriers, their preparation methods, chemical/photoelectronic/mechanical properties, and their role in device stability, are further discussed. On the basis of these accumulative efforts, predictions for the further development of effective barriers in PSCs are provided at the end of this review.

A high‐performance all‐polymer solar cell (PCE of 12.06%) is achieved based on a novel polymer acceptor with a voltage loss of 0.52 eV, which is one of the smallest values reported for all‐polymer solar cells to date.

Abstract

Although the field of all‐polymer solar cells (all‐PSCs) has seen rapid progress in device efficiencies during the past few years, there are limited choices of polymer acceptors that exhibit strong absorption in the near‐IR region and achieve high open‐circuit voltage (V _OC) at the same time. In this paper, an all‐PSC device is demonstrated with a 12.06% efficiency based on a new polymer acceptor (named PT‐IDTTIC) that exhibits strong absorption (maximum absorption coefficient: 2.41 × 10⁵ cm⁻¹) and a narrow optical bandgap (1.49 eV). Compared to previously reported polymer acceptors such as those based on the indacenodithiophene (IDT) core, the indacenodithienothiophene (IDTT) core has further extended fused ring, providing the polymer with extended absorption into the near‐IR region and also increases the electron mobility of the polymer. By blending PT‐IDTTIC with the donor polymer, PM6, a high‐efficiency all‐PSC is achieved with a small voltage loss of 0.52 V, without sacrificing J _SC and FF, which demonstrates the great potential of high‐performance all‐PSCs.

In article number https://doi.org/10.1002/adma.2020014762001476, Xugang Guo and co‐workers develop two ultranarrow‐bandgap n‐type polymer semiconductors, which enable efficient electron transport in organic thin‐film transistors with a highest electron mobility of 1.72 cm² V⁻¹ s⁻¹ and which deliver remarkable photovoltaic performance with a highest power conversion efficiency of 10.22% and short‐circuit current up to 22.52 mA cm⁻². The emergence of such polymers will guide materials innovation for realizing highperformance fully flexible all‐polymer solar cell modules.