Ligang Yuan

A versatile manufacturing technology, solvent-annealing assisted thermal evaporation (SATE), is introduced to effectively modulate organic film morphology as well as optoelectronic properties. The SATE method produces undoped spiro-OMeTAD layers with high density, good film homogeneity, enhanced conductivity, and remarkable film stability, which leads to a 36% enhancement of power conversion efficiency to 20.02% and remarkable stability. This work demonstrates that SATE can be generally applicable to controllable fabrication of organic thin film and reliable devices.

Abstract

Thermal evaporation (TE) as a scalable and low-cost technique for fabrication of organic hole transport materials (HTMs) typically produces low photovoltaic performance and poor device reproducibility in the application of perovskite solar cells (PSCs), and there is a clear need to understand the weaknesses of TE. Here, a versatile manufacturing technology, solvent-annealing assisted thermal evaporation (SATE), enabling effective modulation of organic film morphology as well as optoelectronic properties, is introduced. The SATE method produces undoped spiro-OMeTAD layers with high density, good film homogeneity, enhanced conductivity, and remarkable film stability, all of which are superior to that made by conventional TE. In addition, SATE films eliminate the dopant induced degradation mechanism and simultaneously improve the electrical conductivity of undoped HTMs. Significantly, the resulting devices yield a 36% enhancement of power conversion efficiency (PCE) from 14.68% (TE) to 20.02% (SATE), which is the highest reported PCE for evaporated HTMs in n–i–p PSCs. Moreover, unencapsulated PSC devices with SATE demonstrate an impressive environmental and thermal stability by maintaining 85% of initial performance after 2500 h in air with 30% humidity. The high efficiency with simultaneously improved stability demonstrates SATE can be generally applicable to controllable fabrication of organic thin film and reliable devices.

Homologous PbI₂ in situ passivation strategy is demonstrated to passivate defect at grain boundaries of black-phase FAPbI₃ film via methylamine chloride-assisted one-step deposition. The excess PbI₂ based self-passivation on the FAPbI₃ device not only enhances the power conversion efficiency from 14.87% to 22.13% but also leads to excellent durability in air, which is the highest PCE for FAPbI₃-based inverted PSCs reported to date.

Abstract

Formamidinium lead iodide (FAPbI₃) has endowed power conversion efficiencies (PCEs) up to 25.5% in regular-structured perovskite solar cells (PSCs) because of its optimal bandgap and enhanced thermal stability. However, the performance of FAPbI₃-based inverted-structured PSCs is unsatisfactory. Herein, four kinds of commonly used hole transport materials (HTMs) are selected, including PEDOT:PSS, PTAA, NiOx, and MeO-2PACz, to study their impact on the methylamine chloride (MACl)-assisted one-step deposition of FAPbI₃ films. It is found that MeO-2PACz is the optimal substrate for stabilizing black-phase FAPbI₃ and the corresponding inverted-structured PSCs show the best photovoltaic performance. Nonetheless, the PCE is restricted by low open-circuit voltage (V _OC) due to non-radiative recombination caused by MACl residues. Therefore, homologous PbI₂ in situ passivation is implemented to passivate defects at grain boundaries. The addition of excess PbI₂ in precursor solution remarkably decreases charge trap densities and elongates carrier lifetimes. As a result, the optimized device achieves an impressive PCE of 22.13%, which is the highest efficiency of FAPbI₃ based on inverted-structured PSCs. Moreover, the best device exhibits free hysteresis and excellent long-term stability, maintaining 92% of the initial PCEs after 800 h aging under ambient conditions.

A bottom-up infiltration method using HCOONH₄ as pre-buried additive in SnO₂ electron transport layer (ETL) enables a cross-layer defect manipulation throughout the SnO₂ ETL, perovskite layer, and their interface, along with a significantly reduced residual stress within perovskite film. As a result of the cross-layer treatment, a record power conversion efficiency of 22.37% (21.90% certified) is achieved on the optimized flexible perovskite solar cells.

Abstract

Halide perovskites have shown superior potentials in flexible photovoltaics due to their soft and high power-to-weight nature. However, interfacial residual stress and lattice mismatch due to the large deformation of flexible substrates have greatly limited the performance of flexible perovskite solar cells (F-PSCs). Here, ammonium formate (HCOONH₄) is used as a pre-buried additive in electron transport layer (ETL) to realize a bottom-up infiltration process for an in situ, integral modification of ETL, perovskite layer, and their interface. The HCOONH₄ treatment leads to an enhanced electron extraction in ETL, relaxed residual strain and micro-strain in perovskite film, along with reduced defect densities within these layers. As a result, a top power conversion efficiency of 22.37% and a certified 21.9% on F-PSCs are achieved, representing the highest performance reported so far. This work links the critical connection between multilayer mechanics/defect profiles of ETL-perovskite structure and device performance, thus providing meaningful scientific direction to further narrowing the efficiency gap between F-PSCs and rigid-substrate counterparts.

Publication date: 15 June 2022

Source: Nano Energy, Volume 97

Author(s): Yu-Jin Kang, Seok-In Na

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.

It is demonstrated that solution engineered perovskite nanocrystals enable efficient electroluminescence and photovoltaics performance within a single device through tailoring the dispersity and interface. It delivers the maximum brightness of 490 W sr⁻¹ m⁻² at 2.7 V and 23.2% electroluminescence external quantum efficiency, as well as 15.23% photovoltaic efficiency.

Abstract

Integrating highly efficient photovoltaic (PV) function into light-emitting diodes (LEDs) for multifunctional display is of great significance for compact low-power electronics, but it remains challenging. Herein, it is demonstrated that solution engineered perovskite nanocrystals (PNCs, ≈100 nm) enable efficient electroluminescence (EL) and PV performance within a single device through tailoring the dispersity and interface. It delivers the maximum brightness of 490 W sr⁻¹ m⁻² at 2.7 V and 23.2% EL external quantum efficiency, a record value for near-infrared perovskite LED, as well as 15.23% PV efficiency, among the highest value for nanocrystal perovskite solar cells. The PV–EL performance is well in line with the reciprocity relation. These all-solution-processed PV-LED devices open up viable routes to a variety of advanced applications, from touchless interactive screens to energy harvesting displays and data communication.

Long-chain n-heptylamine is introduced via antisolvent engineering into a formamidine (FA)-based perovskite film, which promotes the formation of α-FAPbI₃ at room temperature in humid air via intermolecular exchange behavior. The champion device delivers a power conversion efficiency of 23.7% (certificated 22.76%) with negligible hysteresis and superior stability.

Abstract

Preparation of high-performance perovskite solar cells without strict environmental control is an inevitable trend of commercialization. Humidity is considered the main factor hindering perovskite performance. Formamidine (FA)-based perovskites suffer from the instability of photoactive black α-FAPbI_3, especially in humid air, and numerous defects in the surface and bulk of perovskite films limit their performance. In this work, long-chain n-heptylamine (nHA) is introduced via antisolvent engineering into an FA-based perovskite film. nHA removes the negative intermediate adduct and promotes the formation of α-FAPbI₃ at room temperature in humid air via intermolecular exchange behavior. Moreover, the existence of nHA in the final perovskite film also reduces the defects and suppresses ion migration. The champion device delivers a power conversion efficiency (PCE) of 23.7% (certificated 22.76%) with negligible hysteresis, and the fabricated devices exhibit superior reproductivity. The device stability is also enhanced, maintaining 95% of its initial PCE after 1500 h in ambient air. Moreover, the PCE has no attenuation at the maximum power point under continuous 1-sun light soaking for 500 h. The universality of this method is also demonstrated by other perovskite compositions, including methylamine lead iodine (MAPbI₃) and FA _x MA_{1− x} PbI₃ in humid air.

Bulk and surface treatment of formamidium lead iodide perovskite with chlorine-based compounds promote an enhancement of the solar cell photovoltaic conversion efficiency (PCE), by simultaneously improving the active layer crystallinity and morphology, thus increasing the short-circuit current density, and suppressing nonradiative losses, boosting the device open-circuit voltage.

Defect-mediated recombination losses limit the open-circuit voltage (V _OC) of perovskite solar cells (PSCs), negatively affecting the device's performance. Bulk and dimensional engineering have both been reported as promising strategies to passivate shallow defects, thus improving the photovoltaic conversion efficiency (PCE). Here, a combined bulk and surface treatment employing chlorine-based compounds is employed. Methylammonium chloride (MACl) is used as a bulk additive, while 4-methylphenethylammonium chloride (MePEACl) is deposited onto the perovskite surface to produce a low-dimensional perovskite (LDP) and reduce nonradiative recombination. Through structural and morphological investigations, it can be confirmed that bulk and surface doping have a beneficial effect on the film morphology and its overall quality, while electroluminescence (EL) and photoluminescence (PL) analyses demonstrate an increased and more homogeneous emission. Applying this double passivation strategy in PSC fabrication, a boost is observed in both the short-circuit current density and the V _OC of the devices, achieving a champion 21.4% PCE while improving device stability.

Publication date: 15 August 2022

Source: Chemical Engineering Journal, Volume 442, Part 1

Author(s): Shengwen Li, Junmin Xia, Chao Liang, Zhaorui Wen, Zhen Mu, Kaiyang Wang, Hao Gu, Shiliang Mei, Hui Pan, Jiangzhao Chen, Guichuan Xing, Shi Chen

Efficiency and stability of the air-processed Si-based near-infrared perovskite light-emitting devices have been enhanced by anti-solvent engineering. PMMA and TBAPF₆ are co-doped in anti-solvent to passivate defects and protect perovskite in air-ambient. With the co-doped perovskite, the efficiency of the device increases to 10.4% with a half-life of over 50 min.

Abstract

The preparation of high-efficiency perovskite light-emitting devices (PeLEDs) in the air-ambient has always been a challenge. Herein, the authors propose a Si-based near-infrared air-processed PeLED through the anti-solvent engineering. Two materials, poly(methyl methacrylate) (PMMA) and tetrabutylammonium hexafluorophosphate (TBAPF₆) are co-doped into the anti-solvent, the former protects the perovskite from degradation in a high-humidity atmosphere, and the latter passivates the defects on perovskite surface and increases the conductivity. Through the anti-solvent engineering, the efficiency of PeLEDs has been significantly enhanced and obtains a maximum external quantum efficiency (EQE) of 10.4%, which is the highest among similar devices. This work shows that it is possible to prepare high-efficiency near-infrared PeLEDs in air-ambient through a simple method.

Strategies for improving the performance of perovskite-based solar cells, light emitting diodes, and photodetectors by integrating different quantum dots through the enhancement of interface controlled nucleation, stability, and charge transport of perovskite layer are critically analyzed and summarized.

Abstract

Metal halide perovskites having high defect tolerance, high absorption characteristics, and high carrier mobility demonstrate great promise as potential light harvesters in photovoltaics and optoelectronics and have experienced an unprecedented development since their occurrence in 2009. Semiconductor quantum dots (QDs), on the other hand, have also been proved to be very flexible toward shape, dimension, bandgap, and optical properties for constructing optoelectronic devices. Of late, a strategic combination of both materials has demonstrated extraordinary promise in photovoltaic applications and optoelectronic devices. Combining QDs and perovskites has proved to be quite an effective strategy toward the formation of pinhole-free and more stable perovskite crystals along with tunability of other properties. To boost this exciting research field, it is imperative to summarize the work done so far in recent years to provide an intriguing insight. This review is a critical account of the advanced strategy toward combining these two fascinating materials, including their different synthetic approaches regarding heteroepitaxial growth of perovskite crystals on QDs, carrier dynamics at the interface and potential application in the field of solar cells, light emitting diodes, and photodetectors.

Publication date: 1 July 2022

Source: Chemical Engineering Journal, Volume 439

Author(s): Huan Bi, Yao Guo, Mengna Guo, Chao Ding, Shuzi Hayase, Tao Mou, Qing Shen, Gaoyi Han, Wenjing Hou

Publication date: 1 July 2022

Source: Chemical Engineering Journal, Volume 439

Author(s): Shumin Huang, Peiyu Li, Jing Wang, Jacob Chih-Ching Huang, Qifan Xue, Nianqing Fu

Publication date: 1 July 2022

Source: Chemical Engineering Journal, Volume 439

Author(s): Xin Yin, Jifeng Zhai, Pingfan Du, Wei-Hsiang Chen, Lixin Song, Jie Xiong, Frank Ko

The increase in butylammonium iodide (BAI) steric hindrance weakens its diffusion to grain boundary, resulting in excessive BAI residue on the surface of perovskite films. Because diffusion to grain boundary affects the passivation of grain boundaries and excessive BAI on the surface blocks hole transport, the photovoltaic performance of the device decreases gradually with the increase in BAI steric hindrance.

The efficiency and stability of perovskite solar cells (PSCs) can be effectively improved by interfacial modification with butylammonium iodide (BAI). However, the steric hindrance of BAI is not explored. Herein, BAI with different steric hindrances, that is, n-BAI, iso-BAI (i-BAI), and tert-BAI (t-BAI), are systematically studied as interface modification materials between (FAPbI₃)_0.95(MAPbBr₃)_0.05 and spiro-OMeTAD in PSCs. It is found that the efficiency and humidity stability of devices gradually increase in the order of t-BAI-, i-BAI-, n-BAI-modified ones. This seems that the larger steric hindrance hinders BAI diffusion to the grain boundary, resulting in the reduction of grain boundary passivation and the residue of excessive BAI on the surface of perovskite films. Excessive BAI is equivalent to new defects and can block hole transport. As the steric hindrance increases from n-BAI to i-BAI, and further to t-BAI, the device with n-BAI modification shows the highest power conversion efficiency (PCE) of 20.67% with excellent stability in air with a humidity of 20–30%, keeping 80% of the original PCE after 60 days. It is believed that this study can guide the structural selection of modified materials at the interface between perovskite and hole transport layer with n–i–p structure.

4-bromobenzenesulfonyl chloride is introduced to modify the perovskite film to improve crystal quality, reduce nonradiative recombination, and passivate surface defects. As a consequence, the optimized device achieves a champion power conversion efficiency of 21.84%, and the efficiency can retain almost 80% of the original value after 1200 h.

Perovskite photovoltaics have drawn tremendous attention due to their excellent photoelectric performance and possess promising potential in the field of renewable energy. Although the photoelectric conversion efficiency of perovskite solar cells has made a quantum leap, stability is still a limitation to its long-term development and has become the main issue that needs to be solved urgently. The defects in the perovskite films and at the grain boundaries are important factors affecting the stability of perovskite photovoltaics. It is reported that the surface defect of the perovskite film is two to four orders of magnitude higher than the bulk defect. Herein, 4-bromobenzenesulfonyl chloride to modify the surface defects of perovskite films is introduced. Through the interaction between S = O in 4-bromobenzenesulfonyl chloride and the bare Pb²⁺ in the perovskite film, the crystal quality of the perovskite film is significantly improved and the surface defects are effectively passivated. The optimized device achieves a champion power conversion efficiency of 21.84%, and the efficiency can retain 92% of the initial value after 1200 h. This finding provides a method to improve the device performance of perovskite solar cells.

A combined application of benzylammonium thiocyanate surface modification and methylammonium chloride additive engineering is applied to improve film quality of Cs–FA double-cation perovskite, helping to achieve enlarged and monolithic perovskite grains, better interfacial properties, and passivate the nonradiative recombination centers. As a result, a distinguished power conversion efficiency of 22.3% is realized for gas-quenched inverted p–i–n perovskite solar cells.

Inverted perovskite solar cells (PSCs) prepared by the antisolvent method have achieved power conversion efficiencies (PCEs) of over 23%, but they are not ideal for device upscaling. In contrast, gas-quenched PSCs offer great potential for upscaling, but their performance still lags behind. Herein, the gas-quenched films through both surface and bulk modifications are upgraded. First, a novel surface modifier, benzylammonium thiocyanate, is found to allow remarkably improved surface properties, but the PCE gain is limited by the existence of longitudinally multiple grains. Thus, methylammonium chloride additive as a second modifier to realize monolithic grains is further utilized. Such an integrated strategy enables the average open-circuit voltage of the gas-quenched PSCs to increase from 1.08 to 1.15 V, leading to a champion PCE of 22.3%. Moreover, the unencapsulated device shows negligible degradation after 150 h of maximum power point operation under simulated 1 sun illumination in N₂.

Adopted seed-assisted growth strategy to induce high crystalline, low-bandgap FAPbI₃-based perovskite below the thermodynamic phase-transition temperature (at 100 °C). The α-CsPbBr₃ seeds directly induce hexagonal α-FAPbI₃ crystals during the very initial crystallization period even at ambient temperature. Meanwhile, CsPbBr₃ seeds supplied an oriented template for the following perovskite grains bottom-up growth. The power conversion efficiency reached 22% in methylammonium-free inverted perovskite solar cells.

Abstract

The traditional way to stabilize α-phase formamidinium lead triiodide (FAPbI₃) perovskite often involves considerable additions of methylammonium (MA) and bromide into the perovskite lattice, leading to an enlarged bandgap and reduced thermal stability. This work shows a seed-assisted growth strategy to induce a bottom-up crystallization of MA-free perovskite, by introducing a small amount of α-CsPbBr₃/DMSO (5%) as seeds into the pristine FAPbI₃ system. During the initial crystalization period, the typical hexagonal α-FAPbI₃ crystals (containing α-CsPbBr₃ seeds) are directly formed even at ambient temperature, as observed by laser scanning confocal microscopy. It indicates that these seeds can promote the formation and stabilization of α-FAPbI₃ below the thermodynamic phase-transition temperature. After annealing not beyond 100 °C, CsPbBr₃ seeds homogeneously diffused into the entire perovskite layer via an ions exchange process. This work demonstrates an efficiency of 22% with hysteresis-free inverted perovskite solar cells (PSCs), one of the highest performances for MA-free inverted PSCs. Despite absented passivation processes, open-circuit voltage is improved by 100 millivolts compared to the control devices with the same stoichiometry, and long-term operational stability retained 92% under continuous full sun illumination. Going MA-free and low-temperature processes are a new insight for compatibility with tandems or flexible PSCs.

The present work demonstrates an efficient strategy of synchronously passivating dual defects with low formation energies via terdentate anchoring by the multifunctional molecule of 1,10-phenanthrolin-5-amine, which could serve as an efficient interfacial mediator and consequently boost the power conversion efficiency up to 24.06%.

Abstract

The ionic nature endows halide perovskites with intrinsic interfacial defects in the formed polycrystalline films, thus imposing the challenge of synchronously passivating these defects with low formation energies that directly account for the unsatisfied performance of perovskite solar cells (PSCs). By virtue of the theoretically proven capability of a three to four times enhancement of the formation energy of each defect of Pb-I antisite (Pb_I) and iodine vacancy (V_I), a new passivation molecule of 1,10-phenanthrolin-5-amine (PAA) is intentionally explored to synchronously passivate the dual defects. The pronounced passivation effect is experimentally verified by the sharp enhancement of the open-circuit voltage in ternary PSCs from the original 1.118 up to 1.207 V, as well as the construction of PAA-modified formamidinium lead iodide PSCs with a champion efficiency up to 24.06%, thus providing a universal alternative of addressing interfacial charge carrier dynamics and operational stability of PSCs that are bothered by the multiple interfacial defects.

A solution-process synthesis strategy is developed for controllable epitaxial growth of long-range ordered micro-nano arrays on MAPbI₃ single crystal (SC) surface. In-plane and out-plane orientated growth can be regulated by introducing a 0D perovskite hydrated intermediate phase, which attributes potential applications in functional imaging and polarized emission.

Abstract

Fabrication of organic–metal-halide perovskite micro-nano array structures draws attention to the potential application in polarized light, high-resolution X‑ray imaging, light-emitting diodes, and lasers. However, it is still challenging to achieve the growth of controllable long-range ordered nanostructure arrays by chemical solution-based techniques. Herein, controllable epitaxial growth of long-range ordered micro-nano arrays on MAPbI₃ single crystal (SC) surface is reported. A hydrated intermediate phase is found that can effectively regulate in-plane and out-plane orientated growth, respectively. This is attributed to the regulation of growth thermodynamics by hydration 0D perovskite intermediate phase enabling free recombination of PbI₄ ^2– octahedral cages. Further, it is found that the degree of hydration is the key to the realization of in-plane and out-plane growth. Meanwhile, polarization emission and amplified spontaneous emission property are observed in highly oriented nanorod arrays with potential applications in anti-counterfeiting polarized emission.

The performance of Ca²⁺-CsPbBr₃ quantum dot-based light emitting diodes (QLEDs) is improved by utilizing the localized surface plasmon resonance effects of a Au nanospheres (NSs) layer. Benefiting from the precise modulation of the distance between the quantum dot (QD) layer and the Au NS layer, the diameter, and spacing of Au NSs, the external quantum efficiency and luminance of the device are improved 2.5-fold and 3.8-fold, respectively.

Abstract

In recent years, CsPbX₃ (X = Cl, Br, I) perovskite quantum dots (QDs) have been considered as the most promising materials for light-emitting diodes (LEDs). However, the advances of CsPbX₃ quantum dot-based light emitting diodes (QLEDs) still lagged behind inorganic III–V LEDs and other organic LEDs. Herein, a strategy to improve the performances of perovskite QLEDs is reported by utilizing the localized surface plasmon resonance (LSPR) effects of Au nanospheres (NSs). It is accomplished by introducing a Au NS layer into the electron transport layer of Ca²⁺-CsPbBr₃ QLEDs, where the diameter and spacing of Au NSs and the interaction distance between the Ca²⁺-CsPbBr₃ QD and Au NS layers are modulated, according to the theoretical simulation of Finite-difference time-domain. As a result, the photoluminescence quantum yield of Ca²⁺-CsPbBr₃ QD layer is improved from 31.5% to 73.3%. Finally, the luminance of Ca²⁺-CsPbBr₃ QLEDs is improved from 16824 to 63931 cd m^–2 and external quantum efficiency (EQE) is improved from 4.2% to 10.5%. The radiative transition rate can be remarkably modulated from 0.7 × 10⁷ to 6.6 × 10⁷ s^–1. The enhancement in luminance and EQE are the best values in the LSPR modified perovskite QLEDs and the strategy offered in this work fits with other LEDs and optoelectrical devices.

Safer Ink Systems

In article number 2100567, Richard Swartwout and co-workers demonstrated the coating performance of their new, safer solvent ink mixture with an effective permissible exposure limit 10x higher than traditional DMF/DMSO ink systems. Regulatory requirements limit exposure to solvent vapors generated from ink-based coating processes. For perovskite photovoltaics, this requires new ink formulations that exclude traditionally hazardous solvents while simultaneously coating uniformly at scale.

Tandem Solar Panels

In article number 2100493, Michele De Bastiani, Stefaan De Wolf, and co-workers outlined that perovskite/silicon tandem solar panels have a terrific potential to deploy green electricity with outstanding performance. The panels will find great applications in both the residential and the utility-scale market. Particularly in hot climates they can capitalize the solar spectrum more effectively compared to mainstream technologies.