Chen Weijie

Herein, an efficiency of 19.1% with near-zero hysteresis for a low-temperature planar n–i–p perovskite module (11 cm² aperture area, 91% aspect ratio) by avoiding dimethyl sulfoxide detrimental effect, by phenethylammonium iodide defect passivation and by optimized interconnections engineering is demonstrated. The scaling-up loss from cell to module is about 8%, showing homogeneous and defect-free layers, and high reproducibility.

In few years, perovskite solar devices have reached high efficiency on lab scale cells. Upscaling to module size, effective perovskite recipe and posttreatment are of paramount importance to the breakthrough of the technology. Herein this work, the development of a low-temperature planar n–i–p perovskite module (11 cm² aperture area, 91% geometrical fill factor) is reported on, exploiting the defect passivation strategy to achieve an efficiency of 19.1% (2% losses stabilized) with near-zero hysteresis, that is the most unsolved issue in the perovskite photovoltaic technology. The I/Br (iodine/bromide) halide ion ratio of the triple-cation perovskite formulation and deposition procedure are optimized to move from small area to module device and to avoid the detrimental effect of dimethyl sulfoxide (DMSO) solvent. The organic halide salt phenethylammonium iodide (PEAI) is adopted as surface passivation material on module size to suppress perovskite defects. Finally, homogeneous and defect-free layers from cell to module with only 8% relative efficiency losses, high reproducibility, and optimized interconnections are scaled by laser ablation methods. The homogeneity of the perovskite layers and of the full stack was assessed by optical, morphological, and light beam–induced current (LBIC) mapping characterizations.

Addition of small organic molecules into the electron transport layer of inverted geometry organic solar cells is shown to seed crystallinity in the organic bulk heterojunction. Employing aromatic dicarboxylic acids on solution–gel-prepared zinc oxide electron transport layers, differing molecular morphologies of the active layer, with increased higher face-on orientations improving the power conversion efficiency, are demonstrated.

The performance of non-fullerene, polymer bulk heterojunction (BHJ) organic photovoltaic devices has a significant correlation with the molecular morphology of the donor and acceptor. The authors show that small organic molecules coordinated to a metal oxide, an electron transport seed layer (ETSL), can profoundly modify the donor:acceptor molecular morphology of inverted organic photovoltaic (OPV) devices. Using grazing incidence wide angle X-ray scattering (GIWAXS), the authors show that a PTB7-Th:IEICO-4F BHJ active layer has a higher degree of face-on molecular alignment on ETSL-1 (biphenyl-4,4′-dicarboxylic acid, coordinated to ZnO), whilst for naphthalene-2,6-dicarboxylic acid coordinated to ZnO (ETSL-2), it is reduced. Devices of PTB7-Th:IEICO-4F BHJ prepared on ETSL-1 had a 19.91% increase in the average power conversion efficiency (PCE), a 1.56% increase in the fill factor (FF), and a 16.66 ± 0.2% enhancement in the short circuit current density. The observed improvements are believed to be due to significant modifications to the oxide-BHJ interfacial region of ETSL-1, namely the elimination of nano-ridges and defect centers, along with an enhanced wettability. These factors can be correlated with the enhanced device performances, leading to the conclusion that the modulation of the molecular morphology of donor:acceptor blends by ETSL-1 has a broad impact on improving OPV cell efficiencies.

Herein, the mechanism behind the short-circuit current loss observed upon introducing a 2D passivation layer in p–i–n perovskite solar cells is elucidated. Based on experiments and drift–diffusion simulations, the loss is linked to the inhomogeneity of the 2D passivation layer and the ionic space charge, which reduces the effective charge-carrier diffusion length.

Herein, a strong short-circuit current density (J _SC) loss is observed when using phenetylammonium iodide (PEAI) as n-side passivation in p–i–n perovskite solar cells. Comparing experiments with drift–diffusion simulations, different hypotheses for the origin of the J _SC loss are presented and evaluated. Whereas the optical properties of the investigated cell stack remain unchanged, the internal quantum efficiency of the PEAI-based devices decreases drastically. Strong bulk doping and interface traps are ruled out as the origin of the charge extraction limitation. High-spatial resolution photoluminescence (PL) spectroscopy directly images the inhomogeneity of the PEAI-based quasi-2D perovskite wide-bandgap interlayer, which is found to be crucial for the observed J _SC loss. A 2D drift–diffusion model implemented with mobile ions and an inhomogeneous electron transport layer reproduces the experimental behavior accurately. The ionic space charge distribution under short circuit reduces the effective charge-carrier diffusion length, hindering charge transport toward those domains in the perovskite–electron transport layer interface where electrons can be extracted efficiently. A longer charge-carrier lifetime reduces the J _SC loss, highlighting the importance of suppressed non-radiative bulk recombination, not only for achieving high open-circuit voltages, but also for efficient charge extraction.

Herein, a hot-flow-assisted spin-coating method is proposed to prepare Cs_0.5FA_0.5PbI₃ films in the humid air environment. The presence of trace amount Cs₄PbI₆ not only passivates the defects but also improves the stability of Cs_0.5FA_0.5PbI₃. The carbon electrode–based perovskite solar cells (C-PSCs) with Cs_0.5FA_0.5PbI₃–Cs₄PbI₆ heterostructure film show an efficiency of 16.30%, which is the highest for methylamine-free low-temperature C-PSCs.

The preparation of low-cost, high-stability cell devices is the primary trend in the future development of perovskite solar cells (PSCs). The hole transport layer (HTL)-free carbon electrode-based PSCs (C-PSCs) based on methylamine (MA) free perovskites prepared in the ambient air environment is expected to realize this goal. In MA-free perovskites represented by Cs _x FA_1–x PbI₃, although the increase of Cs content increases the bandgap, Cs _x FA_1–x PbI₃ with high Cs content has superior stability. Herein, a hot flow-assisted (HFA) spin-coating method to prepare Cs_0.5FA_0.5PbI₃ films in the ambient air environment with a wide relative humidity operation window is proposed. Compared with the traditional antisolvent method that requires a dry processing environment, the HFA method can easily prepare high-quality Cs_0.5FA_0.5PbI₃ films in a high-humidity ambient air environment. In addition, it is found that the presence of trace amount of Cs₄PbI₆ can not only passivate the defects of Cs_0.5FA_0.5PbI₃ but also suppress the undesired phase transition. As a result, the in situ formed Cs_0.5FA_0.5PbI₃–Cs₄PbI₆ heterostructure film corresponds to better stability and higher photovoltaic performance than the plain Cs_0.5FA_0.5PbI₃ film. The efficiency of the assembled champion C-PSCs is up to 16.30%, which is currently the highest efficiency for MA- and HTL-free low-temperature C-PSCs.

Publication date: 15 June 2022

Source: Nano Energy, Volume 97

Author(s): Yayu Dong, Jian Zhang, Yulin Yang, Jiaqi Wang, Boyuan Hu, Wei Wang, Wei Cao, Shuang Gai, Debin Xia, Kaifeng Lin, Ruiqing Fan

Processing condition-controlled morphology is demonstrated to evolve toward the equilibrium state via phase separation and the crystallization pathway in PBDB-T:IT-M organic solar cells (OSCs). The cold crystallization behavior of IT-M reflects the subtle changes in different pathways and further correlates with morphology data. The impact of the transition pathway on device performance and stability indicates its importance in instructing device optimization.

Abstract

Controlled morphology of solution-processed thin films have realized impressive achievements for non-fullerene acceptor (NFA)–based organic solar cells (OSCs). Given the large set of donor–acceptor pairs, employing various processing conditions to realize optimal morphology for high efficiency and stable OSCs is a strenuous task. Therefore, comprehensive correlations between processing conditions and morphology evolution pathways have to be developed for efficient performance and stability of devices. Within the framework of the blend system, crystallization transitions of NFA molecules are tracked utilizing the first heating scan of differential scanning calorimeter (DSC) measurement correlating with respective morphology evolution of blend films. Real-time dynamics measurements and morphology characterizations are combined to provide optimal morphology transition pathways as NFA molecules are shown to be released from the mixed-phase to form balanced ordered packing with variant processing conditions. Polymer:NFA films are fabricated using blade coating incorporating solvent additive or thermal annealing as processing conditions as a correlation is formulated between performance and stability of solar cells with morphology transition pathways. This work demonstrates the significance of processing condition-controlled transition pathways for the realization of optimal morphology leading to superior OSC devices.

A multifunctional chlorobenzenesulfonic potassium salt is developed to modify regular perovskite solar cells in order to inhibit charged defects at the SnO₂/perovskite buried interface, suppressing the recombination of carriers and hysteresis. The reported devices demonstrate a champion power conversion efficiency of 24.27% and a champion open-circuit voltage up to 1.191 V.

Abstract

The interfacial properties for the buried junctions of the perovskite solar cells (PSCs) play a crucial role for the further enhancement of the power conversion efficiency (PCE) and stability of devices. Delicate manipulation of the interface properties such as the defect density, energy alignment, perovskite film quality, etc., guarantees efficient extraction and transport of photogenerated carriers. Herein, chlorobenzenesulfonic potassium salts are presented as a novel multifunctional agent to modify the buried tin oxide (SnO₂)/perovskite interface for regular PSCs. The increasing number of carbon-chlorine bonds (CCl) in 2,4,5-trichlorobenzenesulfonic potassium (3Cl-BSAK) exhibit efficient interaction with uncoordinated Sn, effectively filling oxygen vacancies in the SnO₂ surface. Importantly, synergistic effects of the functional group-rich organic anions and the potassium ion are achieved for reduced defect density, carrier recombination, and hysteresis. A champion PCE of 24.27% and the open-circuit voltage (V _OC) up to 1.191 V for modified devices are obtained. The unencapsulated devices maintain 80% of their initial PCE after aging at 80 °C for 800 h in the atmosphere and 95% after aging for 100 d. With 3Cl-BSAK decoration, a high efficiency semitransparent PSC with a PCE of 12.83% and an average visible light transmittance (AVT) over 27% is also obtained.

An internal encapsulation strategy is developed to comprehensively passivate vacancy defects inside the device and block the channels for iodide ion diffusion or migration. The internal encapsulation strategy helps to achieve sequential deposited perovskite solar cells with efficiency > 24% as well as excellent stability, with 88% remaining power conversion efficiency compared to the maximum power point tracking measurement after 1000 h.

Abstract

External encapsulation technique as a straightforward craft process has been adopted to prevent the infiltration of moisture and oxygen, thereby improving environmental stabilities of lead halide perovskite solar cells (PSCs). However, irreversible light-induced degradation originating from various vacancies and ion diffusion or migration inside the device cannot be efficiently solved by external encapsulation. Herein, an internal encapsulation strategy by introducing NbCl₅ at the buried tin oxide/perovskite interface and spin-casting n-butylammonium bromide on top of perovskite is developed to comprehensively passivate the vacancies and hence block the channels for ion diffusion or migration. The internal encapsulation strategy results in better homogeneous electron transport layer and effective vacancy passivation at the buried interface and simultaneously generates a more homogeneous, better crystallized perovskite in the vertical direction with significantly reduced residual PbI₂. Furthermore, fewer oxygen vacancies and formation of ultrathin Nb₂O₅ lead to a better interfacial energy level alignment for electron transfer. As a result, power conversion efficiency (PCE) of the resulting PSCs is as high as 24.01%. More importantly, the device demonstrates an excellent stability, retaining 88% of its initial PCE at its maximum power point tracking measurement (under 100 mW cm^–2 white light illumination at ≈55 °C temperature, in N₂ atmosphere) after 1000 h.

Publication date: July 2022

Source: Nano Energy, Volume 98

Author(s): Dou Luo, Zhengyan Jiang, Wanli Yang, Xugang Guo, Xuehui Li, Erjun Zhou, Gongqiang Li, Lanqing Li, Chenghao Duan, Chengwei Shan, Zhaojin Wang, Yuheng Li, Baomin Xu, Aung Ko Ko Kyaw

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.

An energy-level-aligning quaternary material system is reported with an ultra-wide bandgap and deep-highest occupied molecular orbital (HOMO) level polymer donor (PhI-Se) and an upshifted-HOMO nonfullerene acceptor (BTP) as the guests. The addition of PhI-Se and BTP greatly improves the toluene-processed active layer film quality and solar cell performance, yielding 17% efficiency. The host binary device only shows 13.1% efficiency when processed with toluene.

Low and unbalanced charge mobilities result in low short-circuit current density (J _SC) and small fill factor (FF), which greatly limits the power conversion efficiencies (PCEs) of polymer solar cells (PSCs) processed with green solvents. Herein, a unique quaternary material system (PM6:BTP-BO-4F:BTP:PhI-Se) is reported, which uses an upshifted highest occupied molecular orbital (HOMO) acceptor guest (BTP) and a deep-HOMO, ultra-wide bandgap polymer donor guest (PhI-Se) as quaternary strategy to align energy levels and improve morphology, leading to open-circuit voltage (V _OC) (from 0.812 to 0.851 V), FF (from 66.1% to 76.7%), and J _SC (from 24.4 to 26.1 mA cm⁻²) increased simultaneously, hence obtaining PCEs of 17.0% processed with toluene. When processed with chlorobenzene (CB), 18.2% efficiency is obtained. Adding BTP and PhI-Se as the third component increases hole and electron mobilities, respectively, going from 1.32/0.63 × 10⁻⁴ cm² V⁻¹ s⁻¹ for the host binary to 1.56/2.56 and 2.26/2.86 × 10⁻⁴ cm² V⁻¹ s⁻¹ for the BTP and PhI-Se ternary. With both adding, the values shift to 3.69/3.20 × 10⁻⁴ cm² V⁻¹ s⁻¹ for the quaternary blends. The crystalline coherence length (CCL) increases from 18.8 nm to 20.2 nm and 23.6 nm, respectively, for the two ternaries, and then 25.7 nm for the quaternary blend.

The authors made a review of the advancement of organic ionic materials which are utilized for modification engineering in perovskite solar cells. These functional materials are divided into various sections according to their roles in terms of defect passivation on the perovskite surface and grain boundary, energy level alignment, modification of surface morphology, modulation of crystal structure, stabilization of perovskite phase, suppression of ion migration and improvement of stability. The corresponding working mechanisms are thoroughly discussed. Based on the deep understanding, an outlook is proposed at the end.

Perovskite solar cells (PSCs) have achieved excellent power conversion efficiencies comparable to those of silicon-based cells. However, there are still many deficiencies in device stability, performance reproducibility, and hysteresis effect. Some surface modifiers and additives have been introduced in the last few years. Among them, organic ionic materials have attracted much attention due to their advantages of wide selection, strong electronic interaction, and good solubility. In this review, various ionic materials utilized in PSCs during recent several years are summarized. Their mechanisms to improve the device performance are thoroughly discussed, including the defect passivation on the surfaces and grain boundaries, improvement of energy-level alignment, modification of surface morphology, modulation of crystal structure, stabilization of perovskite phase, suppression of ion migration, protection against moisture, and formation of low-dimensional perovskite species. Finally, an outlook on the future research trends is proposed.

An ionic liquid butylammonium acetate (BAAc) is introduced to PbI₂ to tune the crystallization of perovskites to improve device stability. The BAAc-treated devices show better thermal stability with maintaining 79.5% of initial efficiency after 700 h of aging at 85 °C in nitrogen environment, as compared to the pristine device that retained 47.2% of its initial efficiency after 312 h.

Long-term operational stability is a significant challenge for perovskite solar cells to become a commercial photovoltaic technology. Herein, a feasible approach is presented to improve both thermal and environmental stability of organic–inorganic hybrid perovskites by introducing ionic liquid butylammonium acetate (BAAc) to coordinate the PbI₂ precursor solution through strong bonding interactions to tune crystallization of perovskites. Inverted planar solar cells based on BAAc-containing tri-cation perovskites result in a high efficiency of over 20%. More importantly, after 700 h of aging at 85 °C in the nitrogen environment and 650 h storage in the ambient condition with a relative humidity of 35 ± 5%, the BAAc-treated devices are shown to be much more stable as maintained 79.5% and 76.3% of the initial power conversion efficiency, respectively. This work provides a promising strategy to tune crystallization of perovskites to improve long-term stability of perovskite solar cells.

Publication date: July 2022

Source: Nano Energy, Volume 98

Author(s): Sungmin Park, So Hyun Park, Hyunjung Jin, Seongwon Yoon, Hyungju Ahn, Seoeun Shin, Kyungwon Kwak, Sanghee Nah, Eul-Yong Shin, Jun Hong Noh, Byoung Koun Min, Hae Jung Son

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.

Optimized tandem device of the multi-resonance type blue emitter achieves high external quantum efficiency over 25% and extremely long device lifetime of over 500 h at 1000 cd m⁻² and 30000 h at 100 cd m⁻² up to 95% of initial luminance.

Abstract

In this study, a multiple resonance (MR) type blue emitter is synthesized, characterized, and evaluated for highly efficient and stable blue fluorescent organic light-emitting diodes (OLEDs). The MR blue fluorescent emitter has a di-tert-butyl benzene substituent in the MR core structure to minimize quenching mechanisms by intermolecular interaction. The emitter shows a high photoluminescence quantum yield and small full width at half maximum of 22 nm, which realize high external quantum efficiency (EQE) of 11.4% in the single unit OLED and device lifetime up to 95% of the initial luminance (LT₉₅) of 208 h at 1000 cd m⁻² and over 10 000 h at 100 cd m⁻². The optimized tandem device of the new blue emitter achieves high EQE over 25% and extremely long LT₉₅ of over 500 h at 1000 cd m⁻² and 30 000 h at 100 cd m⁻². The lifetime of this work is one of the best data of blue OLED lifetime reported in the literature.

An organic small molecule, 1-bromo-4-(methylsulfinyl)benzene (BBMS), was utilized to reduce the energy disorder of a Sn−Pb alloyed perovskite film via hydrogen bonding and coordination bonding interactions, and the resultant BBMS-treated device showed a high efficiency of over 22 % as well as outstanding long-term stability.

Abstract

Sn−Pb alloyed perovskites have drawn considerable attention because of their appropriate band gap for both single-junction and multi-junction tandem photovoltaics, but the easy-formation of energy disorder still limits their practical applications. Here, we report that the combination of 1-bromo-4-(methylsulfinyl) benzene (BBMS) and SnF₂ greatly reduced the Urbach energy of perovskite films, and largely restrained the oxidation of Sn²⁺. With the help of density functional theory calculations, we clarified the interactions between BBMS and perovskite were responsible for the improvements. As a result, a high efficiency of >22 % was obtained for the Sn−Pb alloy-based solar cells treated by BBMS and SnF₂. More importantly, the BBMS-treated device (devices) demonstrated outstanding stability, retaining 98 % of its original efficiency after heating at 60 °C for 2660 h under N₂.

The sole impact of molecular conformation to device performance is studied by the design of two structural isomers, which suggests that the molecular linearity directly affects the molecular packing and electron reorganization energy, and thus being critical to energy loss and device performance.

Abstract

Two new fused-ring electron acceptor (FREA) isomers with nonlinear and linear molecular conformation, m-BAIDIC and p-BAIDIC, are designed and synthesized. Despite the similar light absorption range and energy levels, the two isomers exhibit distinct electron reorganization energies and molecular packing motifs, which are directly related to the molecular conformation. Compared with the nonlinear acceptor, the linear p-BAIDIC shows more ordered molecular packing and higher crystallinity. Furthermore, p-BAIDIC-based devices exhibit reduced nonradiative energy loss and improved charge transport mobilities. It is beneficial to enhance the open-circuit voltage (V _OC) and short-current current density (J _SC) of the devices. Therefore, the linear FREA, p-BAIDIC yields a relatively higher efficiency of 7.71% in the binary device with PM6, in comparison with the nonlinear m-BAIDIC. When p-BAIDIC is incorporated into the binary PM6/BO-4Cl system to form a ternary system, synergistic enhancements in V _OC, J _SC, fill factor (FF), and ultimately a high efficiency of 17.6% are achieved.