awn

An electrical loss management strategy by using SMe-TATPyr molecule manipulating dopant-free Poly(3-hexylthiophene) (P3HT) has been developed and employed to fabricate efficient and thermally stable CsPbI₂Br solar cells. The P3HT/SMe-TATPyr presents optimized molecular orientation, favorable energy level alignment and effective defect passivation. Based on P3HT/SMe-TATPyr HTLs, the fabricated devices yield a record-high efficiency of 16.93 % for CsPbI₂Br solar cells with dopant-free HTLs.

Abstract

Inorganic cesium lead halide perovskites offer a pathway towards thermally stable photovoltaics. However, moisture-induced phase degradation restricts the application of hole transport layers (HTLs) with hygroscopic dopants. Dopant-free HTLs fail to realize efficient photovoltaics due to severe electrical loss. Herein, we developed an electrical loss management strategy by manipulating poly(3-hexylthiophene) with a small molecule, i.e., SMe-TATPyr. The developed P3HT/SMe-TATPyr HTL shows a three-time increase of carrier mobility owing to breaking the long-range ordering of “edge-on” P3HT and inducing the formation of “face-on” clusters, over 50 % decrease of the perovskite surface defect density, and a reduced voltage loss at the perovskite/HTL interface because of favorable energy level alignment. The CsPbI₂Br perovskite solar cell demonstrates a record-high efficiency of 16.93 % for dopant-free HTL, and superior moisture and thermal stability by maintaining 96 % efficiency at low-humidity condition (10–25 % R. H.) for 1500 hours and over 95 % efficiency after annealing at 85 °C for 1000 hours.

A comparison of simulations and experimental data on transient photoluminescence of halide perovskite films, stacks, and devices is presented. A representation of the decay time as a function of Fermi-level splitting is presented that allows distinguishing the different contributions to the decay that include radiative and non-radiative recombination as well as capacitive charging and discharging of electrodes or interfaces.

Abstract

While transient photoluminescence (TPL) measurements are a very popular tool to monitor the charge-carrier dynamics in the field of halide perovskite photovoltaics, interpretation of data obtained on multilayer samples is highly challenging due to the superposition of various effects that modulate the charge-carrier concentration in the perovskite layer and thereby the measured photoluminescence (PL). These effects include bulk and interfacial recombination, charge transfer to electron- or hole transport layers, and capacitive charging or discharging. Here, numerical simulations with Sentauraus TCAD, analytical solutions, and experimental data with a dynamic range of ≈7 orders of magnitude on a variety of different sample geometries, from perovskite films on glass to full devices, are combined to present an improved understanding of this method. A presentation of the decay time of the TPL decay that follows from taking the derivative of the photoluminescence at every time is proposed. Plotting this decay time as a function of the time-dependent quasi-Fermi-level splitting enables distinguishing between the different contributions of radiative and non-radiative recombination as well as charge extraction and capacitive effects to the decay.

Publication date: September 2021

Source: Nano Energy, Volume 87

Author(s): Guoqing Tong, Dae-Yong Son, Luis K. Ono, Hyung-Been Kang, Sisi He, Longbin Qiu, Hui Zhang, Yuqiang Liu, Jeremy Hieulle, Yabing Qi

Publication date: September 2021

Source: Nano Energy, Volume 87

Author(s): Yousheng Wang, Gowri Manohari Arumugam, Tahmineh Mahmoudi, Yaohua Mai, Yoon-Bong Hahn

Publication date: September 2021

Source: Nano Energy, Volume 87

Author(s): Teoman Ozturk, Erdi Akman, Ahmed Esmail Shalan, Seckin Akin

Tetrabenzo[a,c,g,i]carbazole (TBC) with the combination of carbazole (Cz) and phenanthrene moieties is used as the core unit for hole-transporting materials, which can induce the optimized aggregated state by the extended conjugated system with π–π interactions, contributing to the power conversion efficiency (PCE) of 20.52%, much higher than that of the Cz analogue (18.34%).

Hole-transporting materials (HTMs) are the key component of perovskite solar cells (PSCs) for the role of extracting photogenerated holes, as well as the charge transporting between perovskite layer and metal electrode. Herein, with the aim to enhance the hole mobility by compact molecular packing, the modification of HTMs focuses on the extension of conjugated cores from the commonly used carbazole (Cz) to tetrabenzo[a,c,g,i]carbazole (TBC). Because of the closely cofacial stacking mode of the TBC core with an X-type symmetric structure, the resultant TBC-2,7,11,16-tetra-diphenylamine (TD) can achieve a hole mobility of 6.6 × 10⁻⁴ cm² V⁻¹ s⁻¹ and the corresponding conversion efficiency of 20.52%, higher than that of the analogue Cz-TD (18.34%).

Compared with solution-processing, the vapor deposition strategy has been established as an effective way to fabricate compact and uniform perovskite thin films with excellent versatility and controllability. Thus, an in-time review is critical to summarize the essentials of vapor-based deposition strategies to evaluate their real potential and put challenges into perspective.

The preparation route has striking impacts on the morphology and photovoltaic performance of the solar cells, and the development of a feasible preparation strategy to make such a technology applicable to industry is of utmost significance. Compared with solution processing, the vapor deposition strategy has been demonstrated as an effective way to fabricate compact and uniform perovskite thin films with excellent versatility and controllability. While the vast majority of literature emphasizes solution processing as the deposition method for perovskite solar cells (PSCs), vapor-deposited PSCs are closing the performance gap with numerous research reports of efficiencies above 20%. Thus, an in-time review is critical to summarize the fundamentals of vapor-based deposition strategies to evaluate their real potential and put challenges into perspective. Herein, various vapor deposition routes for the preparation of all-inorganic perovskite films and solar cells are thoroughly addressed. Moreover, the critical factors such as deposition temperature, film thickness, substrate temperature, and annealing conditions that impact the film quality and photovoltaic performance of the perovskite are reviewed. In the end, conclusion and future possibilities of the vapor deposition processes are presented, which will offer constructive guidance for the large-scale fabrication of solar cells.

Herein, crystallization control via solvent engineering for alternating cation (ACI) perovskite (GA)MA _n Pb _n I_3n+1 (<n> = 5, GA = guanidinium, MA = methylammonium) that enables preferential quantum well (QW) distribution within the film and augments the crystallinity and smoothness of the films is proposed. Efficient and stable ACI perovskite solar cells with a power conversion efficiency of 19.18% are realized.

Two-dimensional alternating cation (ACI)-type perovskites self-assemble in solution to form highly ordered periodic stacks with unique physical properties and improved optoelectronic devices. Tailoring composition and distribution of quantum wells (QWs) is of vital importance for the optoelectronic properties and stability, which, however, have been less reported in contrast to their Ruddlesden–Popper (RP) and Dion–Jacobson (DJ) counterparts. Herein, crystallization control via solvent engineering for ACI perovskite (GA)MA _n Pb _n I_3n+1 (<n> = 5, GA = guanidinium, MA = methylammonium) that enables preferential QW distribution within the film and augments the crystallinity and smoothness of the films is proposed. It is found that such morphological improvements are further reflected in the optoelectronic properties, including enhanced charge carrier transport/extraction and suppressed nonradiative charge recombination. Thus, efficient and stable ACI perovskite solar cells with a power conversion efficiency (PCE) of 19.18%, standing the highest among all reported RP, DJ, and ACI (<n> ≤ 5) solar cells, are realized. Meanwhile, the device exhibits superior reproducibility and environmental stability. These findings highlight the importance of crystallization control and pave the way for the realization of high-performance 2D perovskite solar cells.

Herein, selecting methylamine ethanol and acetonitrile as mixed solvent and methylamine hydrochloride as additive, carbon-based fully printed mesoscopic perovskite solar cells are fabricated at room temperature. By incorporating Cl⁻ into the lattice, the work function of the MAPbI₃ perovskite is improved. Ultimately, a champion power conversion efficiency of 15.30% is achieved, accompanied by a high open-circuit voltage of 1.0 V.

Methylamine (MA) and methylamine hydrochloride (MACl) are widely used to prepare highly efficient and stable perovskite solar cells (PSCs). However, MA, as a gas, is difficult to handle and inevitably leads to a large amount of escape, and it is difficult to quantitatively calculate. Herein, selecting a mixture solvent of methylamine ethanol solution (MA-EtOH sol) and acetonitrile (ACN) as a solvent, a new strategy for preparing fully printed mesoscopic perovskite solar cells (MPSCs) at room temperature is first proposed. With the introduction of 20 mol% MACl as additive, the fully printed MPSCs are fabricated without any posttreatment at room temperature via a one-step drop-coating method. As a consequence, the average power conversion efficiency (PCE) of 14.73 ± 0.3% (0.1 cm²) with almost no hysteresis is achieved. Most importantly, the device also exhibits excellent long-term stability when it is unencapsulated. Specifically, the unencapsulated device still retains nearly 100% of its original PCE after 64 days and 88% after 81 days of storage in the dark with a humidity of 50 ± 5% in an atmospheric environment. It provides a new idea for constructing fully printed MPSCs at room temperature in the future.

Publication date: 16 June 2021

Source: Joule, Volume 5, Issue 6

Author(s): Shenghao Li, Manuel Pomaska, Andreas Lambertz, Weiyuan Duan, Karsten Bittkau, Depeng Qiu, Zhirong Yao, Martina Luysberg, Paul Steuter, Malte Köhler, Kaifu Qiu, Ruijiang Hong, Hui Shen, Friedhelm Finger, Thomas Kirchartz, Uwe Rau, Kaining Ding

In this work, the mixed spacer cations 2D perovskite (BDA)_0.8(PEA₂)_0.2MA₄Pb₅X₁₆ films are obtained by employing two typical spacer cations, 1,4-butanediamonium (BDA²⁺) usually for Dion-Jacobson phase and 2-phenylethylammonium (PEA⁺) for Ruddlesden-Popper phase. The device with (BDA)_0.8(PEA₂)_0.2MA₄Pb₅X₁₆ film achieves the power conversion efficiency of 17.21% with excellent thermal and humidity stability.

Abstract

In this article, two different types of spacer cations, 1,4-butanediamonium (BDA²⁺) and 2-phenylethylammonium (PEA⁺) are co-used to prepare the perovskite precursor solutions with the formula of (BDA)_{1- a} (PEA₂) _a MA₄Pb₅X₁₆. By simply mixing the two spacer cations, the self-assembled polycrystalline films of (BDA)_0.8(PEA₂)_0.2MA₄Pb₅X₁₆ are obtained, and BDA²⁺ is located in the crystal grains and PEA⁺ is distributed on the surface. The films display a small exciton binding energy, uniformly distributed quantum wells and improved carrier transport. Besides, utilizing mixed spacer cations also induces better crystallinity and vertical orientation of 2D perovskite (BDA)_0.8(PEA₂)_0.2MA₄Pb₅X₁₆ films. Thus, a power conversion efficiency (PCE) of 17.21% is achieved in the optimized perovskite solar cells with the device structure of ITO/PEDOT:PSS/Perovskite/PCBM/BCP/Ag. In addition, the complementary humidity and thermal stability are obtained, which are ascribed to the enhanced interlayer interaction by BDA²⁺ and improved moisture resistance by the hydrophobic group of PEA⁺. The encapsulated devices are retained over 95% or 75% of the initial efficiency after storing 500 h in ambient air under 40 ± 5% relative humidity or 100 h in nitrogen at 60 °C.

The highest efficiency of 20.39% is obtained for perovskite solar cells based on modified ZnO without annealing and antisolvent process. The perovskite devices exhibit unprecedented environmental stability owing to efficient decreased organic ligands on ZnO surface.

Abstract

Even though ZnO is commonly used as the ETL in the perovskite solar cell (PSC), the reactivity of perovskite deposited thereupon limits its performance. Herein, an ethylene diamine tetraacetic acid-complexed ZnO (E-ZnO) is successfully developed as a significantly improved electron selective layer (ESLs) in perovskite device. It is found that E-ZnO exhibits higher electron mobility and better matched energy level with perovskite compared to ZnO. In addition, in order to eliminate the proton transfer reaction at the ZnO/perovskite interface, a high quality perovskite film fabrication process that requires neither annealing nor antisolvent is developed. By taking advantages of both E-ZnO and the new process, the highest efficiency of 20.39% is obtained for PSCs based on E-ZnO. Moreover, the efficiency of unencapsulated PSCs with E-ZnO retains 95% of its initial value exposed in an ambient atmosphere after 3604 h. This work provides a feasible path toward high performance of PSCs, and it is believed that the present work will facilitate transition of perovskite photovoltaics in flexible and tandem devices since the annealing- and antisolvent-free technology.

The integrated energy conversion–storage systems (ECSISs) based on combining photovoltaic solar cells and energy storage units are promising self-powered devices, which would achieve continuous power supplies for 24 h. Particularly, this novel combination technology can provide new markets for extending the energy application from battery-based electric vehicles and smart grids.

Abstract

With the remarkable progress of photovoltaic technology, next-generation perovskite solar cells (PSCs) have drawn significant attention from both industry and academic community due to sustainable energy production. The single-junction-cell power conversion efficiency (PCE) of PSCs to date has reached up to 25.2%, which is competitive to that of commercial silicon-based solar cells. Currently, solar cells are considered as the individual devices for energy conversion, while a series connection with an energy storage device would largely undermine the energy utilization efficiency and peak power output of the entire system. For substantially addressing such critical issue, advanced technology based on photovoltaic energy conversion–storage integration appears as a promising strategy to achieve the goal. However, there are still great challenges in integrating and engineering between energy harvesting and storage devices. In this review, the state-of-the-art of representative integrated energy conversion–storage systems is initially summarized. The key parameters including configuration design and integration strategies are subsequently analyzed. According to recent progress, the efforts toward addressing the current challenges and critical issues are highlighted, with expectation of achieving practical integrated energy conversion–storage systems in the future.

In article number 2100555, Mansoo Choi, Yun Seog Lee, and co-workers systematically investigate the self-doping effect on the light stability of perovskite solar cells (PSCs). Although both PSCs with Pb-rich and Pb-deficient conditions exhibit similar initial performance, the Pb-rich PSC degrades relatively quickly under light illumination even without H₂O and O₂. The perovskite crystal structure in the foreground represents void, interstitial, and deep-level anti-site defects formed during photo-aging of unbalanced stoichiometry, even under inert ambient conditions.

17.10% efficiency for PM6: Y6-based devices is gained by finely tuning the interface morphology through poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) doping engineering. A comprehensive comparison of dopant solubility affected compatibility with photoactive systems is described. One of the highest efficiencies (15.62%) for all-polymer solar cells is enabled by the dopants.

Abstract

Anode modification is vital for improving device performance of organic solar cells (OSCs). PEDOT:PSS is the most widely applied hole transport layer (HTL) in OSCs. In this work, three kinds of modified HTLs, namely PEDOT:PSS-PA, PEDOT:PSS-TA, and PEDOT:PSS-DA are readily prepared via simple doping of phenylethylamine derivatives into commercially available Al 4083, by modulating the number of hydroxyl groups on the adulterant molecules. All of them exhibit enhanced work functions (WFs) and conductivities. Matching with PM6:Y6 composed active layers, PEDOT:PSS-TA based devices achieves the highest performance with a power conversion efficiency (PCE) of 17.10%, while the PM6:ITC-2Cl system demonstrates a highest PCE of 14.17% in devices with PEDOT:PSS-DA, and the optimal PCE of PM6:PIDTC-T based OSCs is equal to 9.55% while the HTL is PEDOT:PSS-PA. Further investigations reveal that the different adulterants formed various amount of hydrogen bonds in HTLs, inducing dissimilar interfacial morphology and mobility, and thus unidentical degrees of change in recombination. Afterwards, the doping strategy is extended to a newly proposed high-performance system PM6:PY-IT, and successfully drags its efficiency from 14.78% to 15.62%, another world-class breakthrough for all-polymer solar cells. In summary, this study not only achieves a series of OSCs with improved PCEs, but also delivers a deep understanding of PEDOT:PSS improvement.

Layered hybrid perovskites are a viable solution to address stability concerns in perovskite solar cells but suffer from poorer charge transport, limiting performance. This review provides an overview spanning from basic structures of the devices and materials to optoelectronic properties and stability. Additionally, it gives insights on measurement techniques currently being employed with an outlook on emerging technologies.

Abstract

Layered hybrid perovskites (LPKs) have emerged as a viable solution to address perovskite stability concerns and enable their implementation in wide-scale energy harvesting. Yet, although more stable, the performance of devices incorporating LPKs still lags behind that of state-of-the-art, multi-cation perovskite materials. This is typically assigned to their poor charge transport, currently caused by the choice of cations used within the organic layer. On balance, a compromise between efficiency and stability is sought, involving careful control of phase purity and distribution, interfaces and energy/charge transfer processes. Further progress is hindered by the difficulty in identifying the fundamental optoelectronic processes in these materials. Here, the high exciton binding energy of LPKs lead to the formation of multiple photoexcited species, which greatly complicate measurement interpretation. In this light, this review gives an overview of how complementary measurement techniques must be used to separate the contributions from the different species in order to identify device bottlenecks, and become a useful tool to narrow down the limitless list of organic cations. A move away from making compromises to mitigate the impact of poor charge transport is required. The root of the problem must be addressed instead through rational design of the interlayer cations.

The rate of charge transfer (CT) state dissociation in cyanine/fullerene solar cells strongly depends on the electric field but is temperature independent. CT states dissociate via a temperature-independent electron tunneling mechanism through a thin, high-energy potential barrier at the donor–acceptor interface. The results support a new mechanism for charge generation in organic solar cells via carrier tunneling from CT states.

Abstract

Charge transfer (CT) states play a key role in the functioning of organic solar cells; however, understanding the mechanism by which CT states dissociate efficiently into free charges remain a conceptual challenge. Here, the electric field dependent dynamics of charge generation in planar cyanine/fullerene photovoltaic cells is probed over a wide temperature range using time-resolved Stark effect experiments, transient absorption, and photocurrent measurements. Results indicate that dissociation of thermalized CT states is the rate-limiting step for all temperatures. The dissociation rate strongly depends on the field, but is temperature independent. The results also suggest that the yield of generated charges is temperature independent. Model electrostatic calculations illustrate that specific orientations of the cyanine crystal relative to C₆₀ create a repulsive potential for an electron near the interface that is largely due to the quadrupole moment of the unit cell. In combination with the electron-hole coulomb attraction and the electric field-induced barrier lowering, a high-energy potential barrier forms with a narrow width of a few nanometers. It is proposed that charge separation occurs via a field-dependent electron tunneling mechanism through that barrier, which is temperature independent. The results support a thus far overlooked pathway for CT state dissociation via carrier tunneling.

In article number 2100316, Xiao-Tao Hao and co-workers investigate the stabilizing function of alloy states from the perspective of controlling the aggregation of non-fullerene acceptors. The acceptor alloys strengthen the conformational rigidity of BTP-4Cl to restrain the intramolecular vibrations for rapid relaxation of high-energy excited states to stabilize BTP-4Cl. The donor alloys optimize the fibril network microstructure of PM6 to restrict the aggregation of BTP-4Cl.

The harsh environment during the voyage is a challenge for every power system. This is also a challenge for the sailing boats powered by perovskite solar cells (PSCs). In article number 2002078, Guangyong Jin, Yu Duan, and co-workers review the defects passivation for PSCs. It is expected that with the effective passivation strategy and the powerful encapsulation, the commercialization for PSCs could be realized even under the extreme application scenarios.

Publication date: August 2021

Source: Nano Energy, Volume 86

Author(s): Xinxing Liu, Zizheng Wu, Xiaoxiao Fu, Liting Tang, Jianmin Li, Junbo Gong, Xudong Xiao

Publication date: August 2021

Source: Nano Energy, Volume 86

Author(s): LiangLe Wang, Md. Shahiduzzaman, Ersan Y. Muslih, Masahiro Nakano, Makoto Karakawa, Kohshin Takahashi, Koji Tomita, Jean Michel Nunzi, Tetsuya Taima

Stable and efficient CsPbI₃ perovskite light-emitting diodes (PLEDs) are demonstrated by resurfacing perovskite with the aid of inorganic ligands (KI). The resurfaced perovskites show a 7× higher phase stability and higher thermal conductivity than in films with organic ligands. The PLEDs exhibit a record-high external quantum efficiency (EQE) of ≈23 % and a 100-fold improvement in the operating stability compared to previous EQE devices.

Abstract

The all-inorganic nature of CsPbI₃ perovskites allows to enhance stability in perovskite devices. Research efforts have led to improved stability of the black phase in CsPbI₃ films; however, these strategies—including strain and doping—are based on organic-ligand-capped perovskites, which prevent perovskites from forming the close-packed quantum dot (QD) solids necessary to achieve high charge and thermal transport. We developed an inorganic ligand exchange that leads to CsPbI₃ QD films with superior phase stability and increased thermal transport. The atomic-ligand-exchanged QD films, once mechanically coupled, exhibit improved phase stability, and we link this to distributing strain across the film. Operando measurements of the temperature of the LEDs indicate that KI-exchanged QD films exhibit increased thermal transport compared to controls that rely on organic ligands. The LEDs exhibit a maximum EQE of 23 % with an electroluminescence emission centered at 640 nm (FWHM: ≈31 nm). These red LEDs provide an operating half-lifetime of 10 h (luminance of 200 cd m⁻²) and an operating stability that is 6× higher than that of control devices.