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Publication date: March 2022

Source: Nano Energy, Volume 93

Author(s): Xin Yu, Yinhua Lv, Bingyan Xue, Lu Wang, Wanpei Hu, Xinhang Liu, Shangfeng Yang, Wen-Hua Zhang

Publication date: March 2022

Source: Nano Energy, Volume 93

Author(s): Lening Shen, Tao Zhu, Xinwen Zhang, Keven Gong, He Wang, Xiong Gong

Publication date: April 2022

Source: Nano Energy, Volume 94

Author(s): Minna Hou, Ya Wang, Xiufang Yang, Meidouxue Han, Huizhi Ren, Yuelong Li, Qian Huang, Yi Ding, Ying Zhao, Xiaodan Zhang, Guofu Hou

Publication date: April 2022

Source: Nano Energy, Volume 94

Author(s): Hailiang Wang, Huicong Liu, Zijing Dong, Xueyuan Wei, Yongfa Song, Weiping Li, Liqun Zhu, Yang Bai, Haining Chen

Placing an ultrathin layer of dopant-free organic triazatruxene molecules as an interfacial layer improves the hole extraction ability and conductivity of the NiO _x through the intermolecular charge transfer effect. The synergetic approach leads to a substantial performance enhancement in dopant-free DTT-EHDI ₂ -based inverted planar perovskite solar cells, achieving 18.15% power conversion efficiency with negligible hysteresis effect.

Interface engineering is an effective approach to decrease nonradiative recombination and the energy barrier at the perovskite/hole transporting layer (HTL) interfaces. To overcome such limitations, an organic semiconductor (DTT-EHDI ₂ ) is proposed, which is, composed of dithienothiophene (DTT) as the core and a planar triazatruxene incorporating an alkyl chain as the side group. This is noted to be an effective interfacial layer for inverted planar perovskite solar cells (PSCs). The altered interface effectively minimizes the detrimental charge recombination and tailors the photoinduced charge transfer dynamics at the interface of the inorganic HTL/perovskite. The π-conjugation in DTT-EHDI ₂ induces high hole mobility and electrical conductivity via electron-donating properties and strong π–π intermolecular interaction. The synergetic approach leads to a substantial performance enhancement in dopant-free DTT-EHDI ₂ -based inverted planar PSCs, achieving 18.15% power conversion efficiency with negligible hysteresis effect. The present approach provides an effective direction of the cost-effective thiophene derivative as an interfacial agent to escalate the optoelectronic performances in photovoltaics.

Much improved photovoltaic performance by replacing hazardous chlorobenzene with green isobutanol (IBA) in three composition perovskite solar cells is achieved. Preferred (111) crystal orientation, better crystallinity, and enlarged grains are simultaneously achieved in the IBA-treated perovskite film. A novel kind of purer and more stable intermediate phase is found due to different interactions of DMSO with FA⁺ induced by IBA.

Herein, isobutanol (IBA) as a new type of green antisolvent for improving the performance of perovskite solar cells (PSCs) is demonstrated. Compared to the commonly used chlorobenzene (CB), IBA treatment enables a preferred (111) crystal orientation, better crystallinity, enlarged grain size of the perovskite film, and penetrated grain crystal throughout the film. IBA antisolvent can effectively suppress the formation of δ-phase and favor the formation of α-phase during perovskite film crystallization. The superior crystal quality and preferred (111) orientation are attributed to the different interactions of DMSO with FA⁺ induced by the introduction of IBA. As a result, a higher open circuit voltage and improved power conversion efficiency are achieved in three different compositions of PSCs compared with the conventionally used CB antisolvent, suggesting the universality of this method. The results offer instructive insight into searching for a new antisolvent in further potential applications of PSCs.

Perovskite Photovoltaics

In article number 2100842, Nripan Mathews, Subodh Mhaisalkar, Annalisa Bruno, and co-workers investigated low-temperature and scalable electron transport materials for rigid and flexible co-evaporated perovskite solar cells and modules. The scale up of perovskite photovoltaics is a key aspect to bring this technology to commercialization.

Herein, 97% bifacial and semitransparent perovskite solar cells give a high equivalent power output of 21.3 W m⁻² under 1 sun illumination using a white back reflector from the rear side. The results show that the side of illumination has a big impact on the light-soak stability of the devices. Cells show promising light stability with illumination from the rear side.

Semitransparent perovskite solar cells (ST-PSCs) are very attractive due to their potential applications in single junctions for building-integrated photovoltaics (BIPV) and in tandem PV technology using low-bandgap bottom solar cells. Despite the high efficiency achieved, the ST-PSCs still suffer low bifaciality, which can limit their overall energy yield for application in BIPV technologies. Furthermore, the knowledge on the long-term light-soaking stability of the ST-PSC from both illumination sides is required to optimize the energy production in the long term. p−i−n ST-PSCs and semitransparent perovskite solar minimodules with comparable and high efficiencies when illuminated from either the rear or the front sides, resulting in the highest reported bifaciality factor of 97%, are demonstrated. A bifacial equivalent power output of 21.3 W m⁻² is achieved for ST-PSCs under 1 sun illumination on the front side, while using a white back reflector from the rear side with 33.5% reflected albedo. However, the side of illumination has a big impact on the light-soak stability of the ST-PSCs. It is observed that the ST-PSC provides more stable output power under illumination from the rear side (n-side) of the stack.

Publication date: 19 January 2022

Source: Joule, Volume 6, Issue 1

Author(s): Chao Luo, Guanhaojie Zheng, Feng Gao, Xianjin Wang, Yao Zhao, Xingyu Gao, Qing Zhao

This work provides novel insights into the effect of RbF-post-deposition treatments on the Cu(In,Ga)Se₂ absorber surface, and shows the potential of combinatorial analysis based on spectroscopic techniques and machine learning for process monitoring in industrial solar cell manufacturing through device performance prediction at early fabrication stages.

Abstract

The latest record efficiencies of the Cu(In,Ga)Se₂ (CIGSe) photovoltaic technology are driven by heavy alkali post-deposition treatments (PDTs). Despite their positive effect, especially in the V _oc of the devices, their underlying mechanisms are still under discussion. This work sheds light on this topic by performing a high statistics analysis on 620 high efficiency CIGSe solar cells submitted to four different PDT processes (different RbF source temperature) employing a combinatorial approach based on Raman and photoluminescence (PL) spectroscopies. This reveals with statistical confidence subtle differences in the spectroscopic data that relate to the redistribution of defects between the ordered vacancy compound (OVC) and the chalcopyrite phases at the absorber surface. In particular, there is an intertwined decrease of the OVC phase and increase of the so-called “defective chalcopyrite phase.” Additionally, two industry-compatible methodologies for the assessment of the RbF-PDT process and prediction of the V _oc of the final devices with a ±2% error and an efficacy of ≈95% are developed based on analytical and machine learning approaches. These results show that the combined Raman and PL spectroscopic techniques represent a powerful tool for the future development of the CIGSe technology at a research level and for more efficient industrial manufacturing.

A 2D donor–acceptor covalent organic framework nanosheet, [(TPA)₁(TPhT)₁]_CN, is in situ synthesized in a lead iodide layer to regulate the crystallization process of a perovskite film in a sequential deposition method. A covalent organic framework incorporated perovskite solar cell is endowed with a prominent power conversion efficiency of 22.04% and excellent stability.

Abstract

Poor crystallinity of perovskite and extensive defects around grain boundaries are the acknowledged hindrances to obtaining high efficiency and long-term stability for organic metal halide perovskite solar cells (PSCs). Here, a 2D covalent organic framework (2D COF) nanosheets, [(TPA)₁(TPhT)₁]_CN, is first in situ synthesized in a PbI₂ layer with a highly crystalline structure to precisely regulate the crystallization process of perovskite in the sequential deposition method. The existence of 2D COF nanosheets can decelerate intermolecular interdiffusion and induce perovskite crystals to grow along (110) planes with enlarged grain size. Meanwhile, 2D COF nanosheets distributed around the grain boundaries reduce the defect density and promote carriers transporting in the perovskite film. The superior properties of the perovskite film afford the champion PSC device with a power conversion efficiency of 22.04%, which is over 10% higher than the control device. Moreover, the target PSC also demonstrates outstanding long-term stability. It can maintain over 90% of its initial value after 90 days storage in ambient conditions for unencapsulated devices. This work paves a new path for regulating the crystallization process of perovskites via 2D crystalline materials.

This review systematically and comprehensively analyzes the light management issues in all-perovskite tandem solar cells. Besides, the authors go deep in this issue to discuss diverse aspects, including light loss (absorption loss, reflection loss) and light distribution. These issues are important for selecting appropriate materials and designing the structure for highly efficient tandem devices.

Abstract

Developing tandem solar cells is an excellent strategy to break through the Shockley–Queisser limit for single-junction solar cells. All-perovskite tandem solar cells (all-PTSCs) are considered to have great potential by virtue of their advantages of low-cost and low-temperature fabrication. However, complicated light distribution and potential loss of incident light are two issues that hinder the development of all-PTSCs. In this review, the recent progress in light management of two-terminal (2T) and four-terminal (4T) all-PTSCs is summarized. The authors discuss the problems with wide-bandgap and narrow-bandgap sub-cells and optimization strategies for efficient light management of tandem solar cells. Then, main light losses are analyzed, such as parasitic absorption, reflection, and thermal relaxation. Current mismatching is a critical condition that can affect the practical application of 2T tandem solar cells. The authors discuss how the thickness and bandgap of the absorber layer, interference, back reflections, and light distribution influence on light losses in devices and ultimately impact current matching. Also, the impact of light management on the performance of all-PTSCs is comprehensively reviewed. Finally, key issues and the prospects for the future development of all-PTSCs are outlined.

Highly efficient and stable perovskite solar cells via the two-step method are fabricated by introducing a multifunctional 1,8-octanediamine dihydroiodide (ODADI) layer between electron transport layer and perovskite layer. It is found that the interfacial ODADI layer not only facilitates film crystallization but also reduces the buried-interface defect density, delivering a significant enhancement on device efficiency from 19.87% to 22.07%.

Two-step-processed perovskite solar cells show superior reproducibility in terms of stepwise crystallization management. However, the device performance is limited due to the buried-interface defects that are highly dependent on the diffusion process of organic salts into PbI₂. Herein, 1,8-octanediamine dihydroiodide (ODADI) is adopted to develop an alkylammonium predeposition strategy for the high-quality perovskite film. It is found that the pre-deposited ODADI layer not only facilitates the diffusion of organic salts via interaction with PbI₂, but also passivates the buried-interface defects, resulting in a perovskite film with low defect density, high crystallinity, and superior electronic properties. Consequently, the fabricated devices deliver a significant enhancement on power conversion efficiency (PCE) from 19.87 to 22.07%. In addition, a superior long-term stability in glovebox atmosphere, maintaining 96% of the initial PCE after 1000 h, is demonstrated.

CdSe quantum dots (QDs) are used to modulate the crystallization of CsPbI₂Br films in air. The added QDs with bifunctional ligands play a dual role in not only promoting the nucleation process but also retarding the crystal growth of CsPbI₂Br. Finally, the efficiency of carbon-based CsPbI₂Br solar cells is increased from 12.73% to 14.49%, benefitting from the improved film quality.

The high-quality perovskite film is a prerequisite for high-performance optoelectronic devices. Herein, CdSe colloidal quantum dots (QDs) serve as crystallization seeds for the first time to modulate the nucleation and crystal growth processes simultaneously of the CsPbI₂Br film in the ambient environment. As additives, CdSe QDs help promote the nucleation process in the initial stage of perovskite formation. In addition, it is revealed that the surface ligands of QDs also have an essential influence on the subsequent crystal growth of the perovskite film. The bifunctional ligands on the surface of QDs are beneficial in delaying the growth process of perovskite due to the free functional groups at the ends. The CsPbI₂Br film prepared with bifunctional organic ligand-capped CdSe QD additives shows better crystallinity than that of the inorganic ligand-based one due to the dual function of these kinds of QDs in not only promoting nucleation but also retarding crystal growth of CsPbI₂Br crystals. As a result, the high-quality CsPbI₂Br film with a low defect state density is prepared in the ambient environment. The optimized efficiency of the assembled hole-conductor-free carbon-based perovskite solar cells (C-PSCs) is increased from 12.73% to 14.49%, which is one of the best results for all-inorganic C-PSCs.

This study relates to the application of flexible substrates of Cu₂SnS₃ thin film solar cells and performance characteristics according to the thickness of the absorber layer.

Cu₂SnS₃ (CTS) has various crystal structures and a wide bandgap energy range of 0.93–1.77 eV, depending on the crystal structure. The optical properties of CTS are very similar to those of Cu₂ZnSnS₄ (CZTS)-based materials, as reported extensively in the past and is therefore in the spotlight as an absorber material. However, CTS thin film solar cells (TFSCs) are mainly studied on non-flexible substrates, and little research has been focused on flexible substrates. When a flexible substrate is applied to CTS TFSCs, Zn is omitted from CZTS-based materials, reducing raw material costs and enabling a roll-to-roll fabrication process; hence, the economic benefit is doubled. When CTS TFSCs are fabricated on a Mo foil substrate, voids exist at the back interface and the device characteristics markedly deteriorate. To solve this problem, the thickness of the CTS absorber layer is increased in this study by doubling the thickness of the precursor. As a result, Cu, Sn, and S display a more uniform distribution in the absorber layer, which further improves the light-absorbing characteristics of CTS TFSCs. Finally, a device with a power conversion efficiency of 1.31% is obtained.

Ultraviolet (UV)-durable organic solar cells (OSCs) are realized by incorporating a CdSe@ZnS quantum dots (QDs)-modified PEDOT:PSS hole extraction layer (HEL). More than 50% reduction in the power conversion efficiency (PCE) is observed for a PM6:Y6-based control OSC with a PEDOT:PSS HEL, under the 1000 min UV aging test. Whereas a reduction of 35% in PCE is observed for the OSCs with a CdSe@ZnS QDs-modified PEDOT:PSS HEL.

Abstract

Ultraviolet (UV)-durable organic solar cells (OSCs) are realized by incorporating a CdSe@ZnS quantum dots (QDs)-modified PEDOT:PSS hole extraction layer (HEL). The use of the CdSe@ZnS QDs-modified PEDOT:PSS HEL has an obvious improvement in UV-durability of OSCs. A more than 50% reduction in the power conversion efficiency (PCE) is observed for a (PM6:Y6)-based control OSC with a PEDOT:PSS HEL, under the 1000 min accelerated UV (365 nm, 16 W) aging test. Whereas a much reduced reduction of 35% in PCE is observed for the OSCs with a CdSe@ZnS QDs-modified PEDOT:PSS HEL, under the same accelerated UV aging test condition. Results reveal that the Coulombic attraction between the PEDOT units and PSS chains in the PEDOT:PSS layer is disturbed due to the interaction between hydroxyl ligands of the CdSe@ZnS QDs and PSS through hydrogen bond, leading to an increase in the electric conductivity in PEDOT:PSS layer through transforming PEDOT quinoid structure to expanded-coil structure. The use of the CdSe@ZnS QDs-modified PEDOT:PSS HEL also favors the efficient operation of the nonfullerene acceptor (NFA)-based OSCs through maintaining a high built-in potential across the bulk heterojunction. The results demonstrate the importance of the interface engineering to alleviate UV light-induced degradation processes of NFA-based OSCs.

A diaminobenzene dihydroiodide-MA_0.6FA_0.4PbI_{3− x} Cl _x analogous 2D unsymmetrical perovskite film is successfully fabricated and applied as absorber layer to further enhance perovskite solar cell (PSC) performance. High power conversion efficiency (PCE) of 22.34% is obtained for MAPbI_{3− x} Cl _x based PSC. The PCE only reduces by 5% under atmospheric humidity of 30%–40% in 140 d.

Abstract

2D perovskites exhibit limited charge transfer and a stable unsymmetrical structure. Hence, a 2D perovskite solar cell (PSC) is more stable but less efficient than a 3D PSC. An effective combination of good stability and high power conversion efficiency (PCE) is desirable in PSCs. A novel diaminobenzene dihydroiodide-MA_0.6FA_0.4PbI_{3− x} Cl _x analogous 2D unsymmetrical perovskite is designed to further enhance PSC performance. The two amino groups of diaminobenzene dihydroiodide (DD) function similarly as the amino groups of methylammonium and formamidinium ions. Therefore, diaminobenzene dihydroiodide can replace methylammonium and formamidinium and create better bonding interaction with the lead trihalide. The analogous 2D unsymmetrical perovskite not only possesses sufficient charge transfer but also exhibits high stability with an appropriate incorporation of DD. Noticeably, the champion device shows a PCE of 22.34%, setting a new record for an MAPbI_{3− x} Cl _x based PSC. The thermal, illumination, and environmental stability is enhanced by 20%–30%. The improved PCE and stability is attributed to better charge transfer and stable structure.

5-chloroindole (Cl-indole) is introduced into the interface between SnO₂ and perovskite. Cl-indole can form hydrogen bonds with iodine in the perovskite and can also coordinate and passivate Pb²⁺ and Sn⁴⁺ defects to alleviate carrier nonradiative recombination. The pristine device reaches an efficiency of 20.58%, while the modified device achieves an efficiency of 22.47%, along with improved hysteresis effect and stability.

Interface engineering has been proven to be an effective method to improve the performance and stability of perovskite solar cells (PSCs). Herein, 5-chloroindole (Cl-indole) is introduced into the interface of a SnO₂ electron transport layer and perovskite light-absorbing layer to improve the photovoltage performance of the device. The results show that Cl−indole can not only form hydrogen bonds with iodine in the perovskite to optimize the interface contact but also coordinate and passivate the Pb²⁺ and Sn⁴⁺ interface defects to alleviate carrier nonradiative recombination. Compared with the pristine SnO₂-based planar PSCs with a power conversion efficiency (PCE) of 20.58%, the Cl−indole-modified SnO₂-based device achieves a PCE of 22.47%. Meanwhile, the stability of the modified device is effectively improved and the hysteresis effect is reduced. This work demonstrates a promising strategy for high-efficient and stable PSCs by optimizing interface contact and passivating interface defects.

Publication date: 19 January 2022

Source: Joule, Volume 6, Issue 1

Author(s): Zhong Zheng, Jianqiu Wang, Pengqing Bi, Junzhen Ren, Yafei Wang, Yi Yang, Xiaoyu Liu, Shaoqing Zhang, Jianhui Hou

Publication date: 16 February 2022

Source: Joule, Volume 6, Issue 2

Author(s): Wanchun Xiang, Jiahuan Zhang, Shengzhong (Frank) Liu, Steve Albrecht, Anders Hagfeldt, Zaiwei Wang

Amphiphilic supramolecular adhesives with low glass transition temperature and massive hydrogen bonds were designed by random copolymerization of acrylamide and n-butyl acrylate. The adhesive dopant facilitates a dynamic thermal self-healing effect at only 70 °C and contributes to efficient and highly flexible perovskite solar cells.

Abstract

Flexible perovskite solar cells (FPSCs) have attracted great attention due to their advantageous traits such as low cost, portability, light-weight, etc. However, mechanical stability is still the weak point in their practical application. Herein, we prepared efficient FPSCs with remarkable mechanical stability by a dynamic thermal self-healing effect, which can be realized by the usage of a supramolecular adhesive. The supramolecular adhesive, which was obtained by random copolymerization of acrylamide and n-butyl acrylate, is amphiphilic, has a proper glass transition temperature and a high density of hydrogen-bond donors and receptors, providing the possibility of thermal dynamic repair of mechanical damage in FPSCs. The adhesive also greatly improves the leveling property of the precursor solution on the hydrophobic poly[bis(4-phenyl)(2,4,6-trimethylphenyl)]amine (PTAA) surface. PSCs containing this adhesive achieve more than a 20 % power conversion efficiency (PCE) on flexible substrates and a 21.99 % PCE on rigid substrates (certified PCE of 21.27 %), with improved electron mobility and reduced defect concentration.

The authors report stable and durable optoelectronic properties using formamidinium (FA)-based centimeter-long 2D hybrid perovskite high-quality single-crystal controlled by the thickness of two perovskite layers. The 2D hybrid (BA)₂FAPb₂I₇ perovskite single-crystal exhibits tremendously enhanced air stability with long-live photodetector performance compared to its methylammonium counterpart (BA)₂MAPb₂I₇ single-crystal.

Abstract

Solution-processable 2D metal-halide perovskites are highly promising for cost-effective optoelectronic applications due to their intrinsic multiquantum well structure. However, the lack of stability is still a major obstacle in the use of this class of materials in practical devices. Here, the authors demonstrate the stable optoelectronic properties using formamidinium (FA)-based centimeter-long 2D perovskite (BA)₂FAPb₂I₇ high-quality single-crystal controlled by the thickness of two perovskite layers. The large area single-crystal exhibits good crystallinity, phase purity, and spectral uniformity. Moreover, the (BA)₂FAPb₂I₇ single-crystal shows excellent stability at open atmospheric conditions when compared to methylammonium (MA)-based (BA)₂MAPb₂I₇ counterparts. The photodetectors fabricated using 2D perovskite single-crystal on the rigid Si/SiO₂ substrate reveal high photoresponsivity (R _λ)(≈5 A W⁻¹), the fast response time (<20 ms), specific detectivity (D*) (≈3.5 × 10¹¹ Jones), and excellent durability under 488 nm laser illumination. The R_λ and D* values are obtained from the (BA)₂FAPb₂I₇ single-crystal 25 times and three orders magnitudes, respectively, higher than the (BA)₂MAPb₂I₇ single-crystal. Additionally, the perovskite material on flexible polymer substrate reveals good photo-sensing properties in both bending and nonbending states.

A novel ionic liquid, 1-ethyl-3-methylimidazolium hydrogen sulfate (EMIMHSO₄), is employed for managing defects in printed cesium lead triiodide (CsPbI₃) films. The EMIMHSO₄ can succesfully regulate perovskite thin-film growth and strongly coordinate with the undercoordinated Pb²⁺, which enable the achievement of the highest-efficiencies ambient printed CsPbI₃ solar cells, both under 1 sun illumination (20.01%, 100 mW cm⁻²) and indoor light illumination (37.24%, 1000 lux, 365 µW cm⁻²).

Abstract

All-inorganic cesium lead triiodide (CsPbI₃) perovskite is well known for its unparalleled stability at high temperatures up to 500 °C and under oxidative chemical stresses. However, upscaling solar cells via ambient printing suffers from imperfect crystal quality and defects caused by uncontrollable crystallization. Here, the incorporation of a low concentration of novel ionic liquid is reported as being promising for managing defects in CsPbI₃ films, interfacial energy alignment, and device stability of solar cells fabricated via ambient blade-coating. Both theoretical simulations and experimental measurements reveal that the ionic liquid successfully regulates the perovskite thin-film growth to decrease perovskite grain boundaries, strongly coordinates with the undercoordinated Pb²⁺ to passivate iodide vacancy defects, aligns the interface to decrease the energy barrier at the electron-transporting layer, and relaxes the lattice strain to promote phase stability. Consequently, ambient printed CsPbI₃ solar cells with power conversion efficiency as high as 20.01% under 1 sun illumination (100 mW cm⁻²) and 37.24% under indoor light illumination (1000 lux, 365 µW cm⁻²) are achieved; both are the highest for printed all-inorganic cells for corresponding applications. Furthermore, the bare cells show an impressive long-term ambient stability with only ≈5% PCE degradation after 1000 h aging under ambient conditions.