Chen Weijie

Publication date: 1 June 2022

Source: Nano Energy, Volume 96

Author(s): Luyao Zheng, Lening Shen, Tao Zhu, Dong Zhang, Jie Zheng, Xiong Gong

A new class of polymeric hole-transport materials (HTMs) was explored, featuring fluorine-substituted pyrene and specific Pb−Se secondary interactions. Perovskite solar cells (PSCs) using PE10 as dopant-free HTM, afforded an excellent PCE of 22.3 %, positioning it among the best PSCs based on dopant-free HTMs.

Abstract

A new class of polymeric hole-transport materials (HTMs) are explored by inserting a two-dimensionally conjugated fluoro-substituted pyrene into thiophene and selenophene polymeric chains. The broad conjugated plane of pyrene and “Lewis soft” selenium atoms not only enhance the π–π stacking of HTM molecules greatly but also render a strong interaction with the perovskite surface, leading to an efficient charge transport/transfer in both the HTM layer and the perovskite/HTM interface. Note that fluorine substitution adjacent to pyrene boosts the stacking of HTMs towards a more favorable face-on orientation, further facilitating the efficient charge transport. As a result, perovskite solar cells (PSCs) employing PE10 as dopant-free HTM afford an excellent efficiency of 22.3 % and the dramatically enhanced device longevity, qualifying it among the best PSCs based on dopant-free HTMs.

Nature, Published online: 18 March 2022; doi:10.1038/d41586-022-00774-4

Publication date: 16 March 2022

Source: Joule, Volume 6, Issue 3

Author(s): Arsalan Razzaq, Thomas G. Allen, Wenzhu Liu, Zhengxin Liu, Stefaan De Wolf

A newly designed and synthesized asymmetric acceptor TIT-2Cl is elaborately introduced into the PM6:Y6 system to inhibit the over-aggregation of Y6. Due to the formation of vertical phase separation and improved carrier transport, the PM6/Y6:TIT-2Cl-based device achieves better stability and high efficiency approaching 18.18% by combining ternary strategy and layer-by-layer method, which is the highest efficiency reported for PM6:Y6-based devices.

Abstract

Although much research on device engineering have brought about significant improvements in PM6:Y6-based polymer solar cell (PSCs) performance, there is still a lack of relevant research to solve the problems caused by the over-aggregation of Y6 and the long-term stability of the device morphology. Herein, a newly designed and synthesized low-bandgap asymmetric small molecule acceptor TIT-2Cl based on thieno[3,2-b]indole core is elaborately introduced into PM6:Y6-based PSCs to suppress the over-aggregation of Y6 molecules with significantly increased efficiency from 15.78% to 17.00%. Moreover, the addition of TIT-2Cl contributes to improved light harvesting, the lowest unoccupied molecular orbital level of Y6:TIT-2Cl, charge separation, transport, and extraction. Simultaneously, the PSCs are further prepared by using the progressive spin-coating method of layer-by-layer (LBL). Due to the formation of vertical phase distribution and the improvement of carrier transport performance, the champion efficiency of LBL-type ternary PSCs reaches 18.18%, which is the highest efficiency reported for PM6:Y6-based PSCs, along with superior stability and compositional insensitivity. Therefore, the results show that the combination of ternary strategy by incorporating appropriate asymmetric molecules and the LBL method is an effective means to fabricate highly efficient stable PSCs.

Bandgap-stable and efficient CsPbBr _x I_{3− x} perovskite light-emitting diodes (PLEDs) are demonstrated by adopting an in situ inorganic ligand exchange. This strategy enables bandgap-stable mixed-halide perovskites with nanocrystal colloidal stability exceeding 1 year at ambient conditions. The PLEDs exhibit an external quantum efficiency (EQE) of 24.4% and sixfold-enhanced operating stability relative to the most stable prior red perovskite LEDs having EQEs >20%.

Abstract

Instability in mixed-halide perovskites (MHPs) is a key issue limiting perovskite solar cells and light-emitting diodes (LEDs). One form of instability arises during the processing of MHP quantum dots using an antisolvent to precipitate and purify the dots forming surface traps that lead to decreased luminescence, compromised colloidal stability, and emission broadening. Here, the introduction of inorganic ligands in the antisolvents used in dot purification is reported in order to overcome this problem. MHPs that are colloidally stable for over 1 year at 25 °C and 40% humidity are demonstrated and films that are stable under 100 W cm⁻² photoirradiation, 4× longer than the best previously reported MHPs, are reported. In LEDs, the materials enable an EQE of 24.4% (average 22.5 ± 1.3%) and narrow emission (full-width at half maximum of 30 nm). Sixfold-enhanced operating stability relative to the most stable prior red perovskite LEDs having external quantum efficiency >20% is reported.

The dynamics of light soaking (LS) effect, drift-diffusion simulations, and external voltage experiments reveal the correlation of the LS effect with ion migration in perovskite solar cells (PSCs). Furthermore, the introduction of Cs⁺ into perovskite films reduces the density of mobile ions in PSCs, which can not only suppress the LS effect notably but also enhance the long-term stability of PSCs.

Light soaking (LS) effect of perovskite solar cells (PSCs), i.e., the power conversion efficiency (PCE) increases under continuous light illumination (CLI), has attracted a lot of attention recently. Herein, it is reported that a strong LS effect occurs in the FA_xMA_1-xPbI₃ (FAMA) PSC for its PCE increases from 7.5% to 20.5% under CLI. Based on the dynamics of the LS effect, drift-diffusion simulations, and external voltage experiments, it is found that the underlying process for the LS effect is that the generated photovoltage under CLI modulates the distribution of mobile ions in absorber layers increasing charge extraction ability and then alleviating interface recombination, which directly results in the LS effect in FAMA PSCs. In addition, the introduction of Cs⁺ into perovskite films can reduce the density of accumulated mobile ions at the interface between absorber layers and charge-transporting layers in FAMA PSCs. As a result, the PCE of the Cs⁺-doped device increases from 18.7% to 22.4% under CLI demonstrating that the LS effect in the Cs⁺-doped device is suppressed notably. This work reveals the correlation of the LS effect with ion migration and suppresses the LS effect in FAMA PSCs.

The ternary polymer solar cells demonstrate more balanced charge transport properties based on 20% third component, which improves blend film morphology and charge transport channels, where the ternary system with high average visible transmittance over 27% and power conversation efficiency over 12% is more suitable in ternary semitransparent devices than others.

Ternary semitransparent polymer solar cells (ST-PSCs) have great potential to simultaneously improve the power conversion efficiency (PCE) and average visible transmittance (AVT). Non-fullerene acceptor IHIC was synthesized by a simple one-step process under low cost and had an A-D-A structure similar to ITIC and IT-4F. Ternary device based on PM6:Y6:IHIC (20%) demonstrated higher hole and electron mobility (2.78, 3.12 × 10⁻⁴ cm² V⁻¹ S⁻¹) and more balanced charge transport properties (μ _e/μ _h = 1.12) than the host binary device, and the ternary ST-PSC demonstrated a PCE of 12.18% and AVT of 27.07%. Ternary PSCs with 20% ITIC or IT-4F also exhibited more balanced μ _e/μ _h ratios (1.31 and 0.85), but with slightly enhanced short-current circuit density (J _SC) and reduced AVT (23–24%), mainly owing to unavoidable absorption of third component in the visible region. Our conclusion in this work was that the little A-D-A non-fullerene acceptor could improve ternary blend film morphology and charge transport channels and enhanced J _SC and PCE, and PM6:Y6:IHIC (20%) with high AVT over 27% and PCE over 12% was more suitable in ST-PSCs than PM6:Y6:ITIC/IT-4F (20%).

Guanidinium (GA)-rich perovskite films are prepared via an NH₄Br-assisted two-step process in air conditions, in which NH₄Br is introduced to facilitate the transient phase (NH₄PbI₃) formation and reduce voids and pinholes in films. The fabricated carbon-based perovskite solar cells (C-PSCs) in ambient air deliver the highest efficiency of 16.19% and exhibit excellent stability against moisture, heat, and sunlight.

The substitution of a portion of methylammonium (MA) for guanidinium (GA) has been verified to be able to enhance the stability of MA-based devices. However, high-dose guanidinium cation will introduce localized distortions to the perovskite lattice structure and destroy the microstructure of the perovskite films, impairing the stability and reproducibility of perovskite solar cells (PSCs) eventually. Herein, for the first time, the NH₄Br-assisted all-atmospheric two-step process is adopted to fabricate GA-rich (20%) perovskite films. The NH₄Br induces the formation of the intermediate phase NH₄PbI₃ and alleviates the disorder of the octahedron caused by the big GA. Consequently, the modified perovskite film shows increased tolerance for the roughness fluctuation and reduced risk of forming voids and pinholes. The fabricated compact GA-rich perovskite films behave extremely well in photovoltaic performance when assembled as carbon-based perovskite solar cells, delivering a high power conversion efficiency (PCE) of 16.19% and stability against moisture and sunlight. Especially, the unencapsulated devices in ambient air sustain 95.1%, 91.8%, and 95.7% of their initial PCEs after 2400 h of storage, after 1000 h of 65 °C heat environment, and after 800 h of sunlight illumination, respectively.

This review shows the state-of-the art about the innovative strategies to stabilize perovskite nanocrystals in polar environments to improve the efficiency of photo(electro)catalytic solar-driven reactions.

Photo(electro)catalysis (PEC) is a promising strategy to conduct attractive solar-driven reactions such as CO₂ reduction to form added-value products, H₂ production, and organic substrates oxidation, taking advantage of the spatial separation of photocarriers generated in semiconductor-based electrodes. Halide perovskite nanocrystals (PNCs) are attracting increasing attention due to their tunable optical features and band structure, which is pivotal to modulate their oxidizing/reducing power and perform chemical reactions efficiently. However, the defective structure and ionic nature of PNCs make them prone to be unstable in polar media, where most of the relevant solar-driven chemical reactions of interest take place. In this review, an overview of recent strategies to stabilize PNCs in polar solvents is presented, some of them with promising application or already introduced in PEC systems. Perovskite encapsulation, including the formation of heterostructures, surface passivation engineering, and the synthesis of PNCs with intrinsic stability in polar media, is focused upon. Furthermore, perspectives for using stable lead-free PNCs in solar-driven PEC reactions are presented, showing the benefits of this future technology for energy production/transformation.

A dual-source electron beam coevaporation method is used for the controlled deposition of copper-doped nickel oxide and tungsten-doped niobium oxide as hole and electron transport layers, respectively. Perovskite solar cells based on these inorganic carrier-selective layers achieve power conversion efficiencies of 21.32% for a 0.155 cm² device and 19.01% for a 1 cm² device.

Inorganic carrier-selective layers (CSLs), whose conductivity can be effectively tuned by doping, offer low-cost and stable alternatives for their organic counterparts in perovskite solar cells (PSCs). Herein, a dual-source electron-beam co-evaporation method for the controlled deposition of copper-doped nickel oxide (Cu:NiO) and tungsten-doped niobium oxide (W:Nb₂O₅) as hole and electron transport layers, respectively, is used. The mechanisms for the improved conductivity using dopants are investigated. Owing to the improved conductivity and optimized band alignment of the doped CSLs, the all-inorganic-CSLs-based PSCs achieve a maximum power conversion efficiency (PCE) of 20.47%. Furthermore, a thin titanium buffer layer is inserted between W:Nb₂O₅ and the silver electrode to prevent halide ingression and improve band alignment. This leads to a further improvement of PCE to 21.32% and long-term stability (1200 h) after encapsulation. Finally, the large-scale applicability of the doped CSLs by coevaporation is demonstrated for the device with 1 cm² area showing a PCE of over 19%. The results demonstrate the potential application of the coevaporated CSLs with controlled doping in PSCs for commercialization.

A dimensionally graded 2D/3D heterostructure is formed by in situ growing 2D FPEA₂PbI₄ perovskite on top of the 3D wide-bandgap perovskite film, which leads to a high open-circuitvoltage of 1.31 V with a superior small open-circuit voltage loss of 0.43 V in a 1.74 eV perovskite solar cell system.

Wide-bandgap (WBG) perovskite solar cells (PSCs) are important ingredients for tandem solar cells and play a crucial role in next-generation multijunction photovoltaics. Yet, the severe open-circuit voltage loss (V _loss) and stability have not been solved. Herein, a dimensionally graded 2D/3D heterostructure is fabricated by in situ fabricating a 2D FPEA₂PbI₄ capping layer on the surface of the 3D WBG perovskite film. Through this 2D/3D dimensionally graded design, an enhanced build-in potential promotes the oriented transport of photoinduced carriers and reduces the nonradiative recombination, leading to an ultrahigh open-circuit voltage of 1.31 V with a minimum V _loss of 0.43 V in a 1.74 eV WBG perovskite system and a desirable efficiency of 18.06%. A longer photoluminescence lifetime and decreased trap density indicate the reduced trap-assisted nonradiative recombination. Moreover, such a 2D/3D heterostructure exhibits enhanced stability under moisture and heat. This passivation strategy offers an effective approach to achieving high open-circuit voltage WBG PSCs by facile in situ dimensional engineering, which may pave a general way to step forward in achieving high-performance and stable WBG PSCs.

A general strategy to prepare high-quality electron transport layers (ETLs) below 70 °C by ligand exchange on top of the inorganic CsPbI₂Br perovskite absorber layer is proposed. The ETLs possess smooth, dense, and pinhole-free morphologies, a suitable energy-level structure, favorable conductivity, and chemical stability, which give the whole photovoltaic devices high efficiencies and outstanding stabilities.

Inorganic perovskite solar cells (I-PSCs) have attracted great attention due to the high thermal stability of inorganic perovskites versus the organic–inorganic perovskites. To ensure the thermal stability of I-PSCs, using effective and stable inorganic charge-transporting layers (CTLs) to replace organic ones is quite desirable. The use of low-temperature-prepared inorganic CTLs can also lower the total cost of I-PSCs. Herein, a general strategy to prepare high-quality inorganic nanoparticles-based electron transport layers (ETLs) below 70 °C by ligand exchange on top of inorganic perovskites is developed. The ETLs possess a suitable energy-level structure, favorable conductivity, and chemical stability. Furthermore, all-inorganic CTLs-based CsPbI₂Br I-PSCs with p–i–n architecture are fabricated without using any thermally unstable organic components. Consequently, the as-fabricated I-PSCs based on CdS ETLs yielded the highest power conversion efficiency (PCE) of up to 15.04%, among the most efficient CsPbI₂Br inverted PSCs. Inspiringly, the unencapsulated all-layer-inorganic PSCs present outstanding stabilities, which maintained 94.8% and 95.2% of their initial PCEs after aging at 85 °C in the dark and operating under continuous light illumination at 45 °C for 480 h in N₂ atmosphere, respectively.

L-4-fluorophenylalanine (FPA) is introduced in a MAPbI₃ perovskite film as a multifunctional molecular additive achieving comprehensive defect passivation, surface hydrophobicity, and crystallization control. The FPA-modified inverted perovskite solar cell shows a champion efficiency of 21.28% with negligible hysteresis and maintains outstanding long-term stability.

The harmful defects accumulated at surfaces and grain boundaries (GBs) limit the performance and stability of perovskite solar cells (PSCs), which results from the poor crystallization and ion migration. Here, a multifunctional molecular additive L-4-fluorophenylalanine (FPA) is explored for highly efficient and stable inverted PSCs. The multifunction is realized through comprehensive defect passivation, surface hydrophobicity, and crystallization control with the multitude groups, such as the amino and carbonyl groups for passivating the unsaturated lead defects at GBs, and the benzene ring for electron-deficient iodine defects, and the fluorine group for the improvement of crystallization and the inhibition of ions migration. The resulting inverted device shows a champion power conversion efficiency of 21.28% with negligible hysteresis. The unencapsulated FPA-modified devices maintain nearly 90% of the initial performance after high-temperature (85 °C) thermal accelerated aging for 500 h and 85% after aging for 4000 h under ambient conditions, and about 90% of the original efficiency after being maximum power point tracked for 1000 h under continuous illumination. This study provides a multipronged strategy to the future design of PSCs with higher efficiency and enhanced stability.

A 16.52% efficiency all-polymer solar cell is achieved by morphology control of the photoactive layer through adding a low-cost polymer donor, PTQ10, into the PM6:PY-IT blend. Meanwhile, ternary devices exhibit a high tolerance of the photoactive layer thickness, with high power conversion efficiencies of 15.27% and 13.91% at photoactive layer thicknesses of ≈205 and ≈306 nm, respectively.

Abstract

All-polymer solar cells (all-PSCs) have drawn growing attention and achieved tremendous progress recently, but their power conversion efficiency (PCE) still lags behind small-molecule-acceptor (SMA)-based PSCs due to the relative difficulty on morphology control of polymer photoactive blends. Here, low-cost PTQ10 is introduced as a second polymer donor (a third component) into the PM6:PY-IT blend to finely tune the energy-level matching and microscopic morphology of the polymer blend photoactive layer. The addition of PTQ10 decreases the π–π stacking distance, and increases the π–π stacking coherence length and the ordered face-on molecular packing orientation, which improves the charge separation and transport in the photoactive layer. Moreover, the deeper highest occupied molecular orbital energy level of the PTQ10 polymer donor than PM6 leads to higher open-circuit voltage of the ternary all-PSCs. As a result, a PCE of 16.52% is achieved for ternary all-PSCs, which is one of the highest PCEs for all-PSCs. In addition, the ternary devices exhibit a high tolerance of the photoactive layer thickness with high PCEs of 15.27% and 13.91% at photoactive layer thickness of ≈205 and ≈306 nm, respectively, which are the highest PCEs so far for all-PSCs with a thick photoactive layer.

Publication date: 20 April 2022

Source: Joule, Volume 6, Issue 4

Author(s): Jesús Sanchez-Diaz, Rafael S. Sánchez, Sofia Masi, Marie Kreĉmarová, Agustín O. Alvarez, Eva M. Barea, Jesús Rodriguez-Romero, Vladimir S. Chirvony, Juan F. Sánchez-Royo, Juan P. Martinez-Pastor, Iván Mora-Seró

Nature, Published online: 15 March 2022; doi:10.1038/s41586-022-04604-5

Publication date: 1 June 2022

Source: Nano Energy, Volume 96

Author(s): Xinpeng Yao, Benlin He, Jingwei Zhu, Junjie Ti, Lifang Cui, Rui Tui, Meng Wei, Haiyan Chen, Jialong Duan, Yanyan Duan, Qunwei Tang

Publication date: 1 June 2022

Source: Nano Energy, Volume 96

Author(s): Danqin Li, Fushan Geng, Tianyu Hao, Zeng Chen, Hongbo Wu, Zaifei Ma, Qifan Xue, Lina Lin, Rong Huang, Shifeng Leng, Bingwen Hu, Xianjie Liu, Jie Wang, Haiming Zhu, Menglan Lv, Liming Ding, Mats Fahlman, Qinye Bao, Yongfang Li

Publication date: 1 June 2022

Source: Nano Energy, Volume 96

Author(s): Jingxuan Chen, Donglin Jia, Junming Qiu, Rongshan Zhuang, Yong Hua, Xiaoliang Zhang