Chen Weijie

A power conversion efficiency of 17.61% is achieved in organic photovoltaic devices (OPVs) with D18-Cl:PM6:Y6 as active layers. The good compatibility and similar highest occupied molecular orbital levels of D18-Cl and PM6 enable the formation of an alloyed state for efficient hole transport. Energy ransfer from D18-Cl to PM6 should improve the exciton utilization in ternary blend OPVs.

Efficient ternary blend organic photovoltaic devices (OPVs) are built based on a D18-Cl:Y6 host system and star polymer donor PM6 as the third component. A power conversion efficiency (PCE) of 16.89% is achieved in D18-Cl:Y6 host binary OPVs, with a short-circuit current density (J _SC) of 25.31 mA cm⁻², an open-circuit voltage (V _OC) of 0.878 V, and a fill factor (FF) of 75.81%. Upon incorporating appropriate PM6 in active layers, the PCE of optimal ternary blend OPVs can be increased to 17.61%, benefiting from a J _SC of 26.35 mA cm⁻², a V _OC of 0.871 V, and an FF of 76.82%. Polymers D18-Cl and PM6 have good compatibility and similar highest occupied molecular orbital (HOMO) levels, which enable to form D18-Cl:PM6 alloyed states for efficient hole transport in ternary blend active layers. Meanwhile, trap density in ternary blend active layers is decreased by incorporating PM6, which is conducive to weaken charge recombination in ternary blend active layers. The gradually varied V _OC values of ternary blend OPVs can be well explained from the varied HOMO levels of D18-Cl:PM6 alloyed states. The results indicate that two compatible polymer donors with similar HOMO levels have great potential in achieving efficient ternary blend OPVs.

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.

Annealing-free perovskite solar cells with power conversion efficiency of 19.25% are fabricated by doping guanidinium iodine (GAI) in precursor solution. The results indicate that GAI could promote the formation of an intermediate phase. Moreover, the intermediate phase with GAI also becomes more stable, for which its transformation into perovskite crystal becomes relatively slow, the perovskite film quality is also improved.

One of the urgent key points to realize the commercialization of perovskite solar cells (PSCs) with robust and excellent performance is the fabrication of high-quality perovskite film. Nevertheless, a traditional thermal annealing (TA) technology is always necessary for a high crystallization perovskite film, and previous reports have suggested that TA could induce heterogeneous nucleation which is inconducive for the formation of smooth and uniform perovskite film, as well as time and cost consuming. Herein, an approach for the annealing-free high-quality perovskite film via the introduction of guanidinium iodine (GAI) is proposed. The organic molecule guanidinium (GA⁺) has a large ionic radius, and this could control the crystallizing rate of annealing-free perovskite film. Ultimately, a perovskite film with larger grain size and lower defect density is acquired through doping 0.10 mol mL⁻¹ GAI in the precursor solution. Moreover, the fabrication of the electron transfer layer and hole transfer layer is further realized at room temperature. Thus, all room temperature, annealing-free high-performance PSCs are demonstrated. Notably, a GAI-doped device with an outstanding power conversion efficiency (PCE) of 19.25% is obtained, much higher than 16.78% of the pristine device.

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.

Organic photovoltaic cells with enhanced photovoltaic performance and long-term stability are achieved via introducing a cross-linkable material (c-PCBSD) as an interfacial modification layer on the surface of zinc oxide and as the third component into the PBDB-TF:Y6 system OPV cells, which provides a new idea for device engineering.

Abstract

Improving power conversion efficiencies (PCEs) and stability are two main tasks for organic photovoltaic (OPV) cells. In the past few years, although the PCE of the OPV cells has been considerably improved, the research on device stability is limited. Herein, a cross-linkable material, cross-linked [6,6]-phenyl-C61-butyric styryl dendron ester (c-PCBSD), is applied as an interfacial modification layer on the surface of zinc oxide and as the third component into the PBDB-TF:Y6-based OPV cells to enhance photovoltaic performance and long-term stability. The PCE of the OPV cells that underwent the two-step modification increased from 15.1 to 16.1%. In particular, such OPV cells exhibited much better stability under both thermal and air conditions because of the decreased number of interfacial defects and stable interfacial and active layer morphologies. The results demonstrated that the introduction of a cross-linkable fullerene derivative into the interfacial and active layers is a feasible method to improve the PCE and stability of OPV cells.

Nature Communications, Published online: 21 May 2021; doi:10.1038/s41467-021-23291-w

Nature Photonics, Published online: 20 May 2021; doi:10.1038/s41566-021-00809-8

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

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.

A stable α-FAPbI₃ perovskite phase is achieved by employing benzylammonium iodide (BzI), which is elucidated by solid-state NMR spectroscopy and X-ray scattering measurements to obtain perovskite solar cells based on the FAPbI₃(BzI)_0.25 composition with power conversion efficiencies exceeding 20% accompanied by enhanced shelf-life and operational stability, maintaining 80% of the performance after one year at ambient conditions.

Abstract

There is an ongoing surge of interest in the use of formamidinium (FA) lead iodide perovskites in photovoltaics due to their exceptional optoelectronic properties. However, thermodynamic instability of the desired cubic perovskite (α-FAPbI₃) phase at ambient conditions leads to the formation of a yellow non-perovskite (δ-FAPbI₃) phase that compromises its utility. A stable α-FAPbI₃ perovskite phase is achieved by employing benzylammonium iodide (BzI) and the microscopic structure is elucidated by using solid-state NMR spectroscopy and X-ray scattering measurements. Perovskite solar cells based on the FAPbI₃(BzI)_0.25 composition achieve power conversion efficiencies exceeding 20%, which is accompanied by enhanced shelf-life and operational stability, maintaining 80% of the performance after one year at ambient conditions.

Ultrathin and ultra-lightweight organic solar cells (total thickness of less than 3 μm) with a stabilized power conversion efficiency of 15.5% and unprecedented power-per-weight of 32.07 W g⁻¹ at a weight of 4.83 g m⁻² are realized, which could be applied to almost any surface of wearable electronic devices, and can withstand the associated mechanical deformation.

Abstract

Ultraflexible and ultra-lightweight organic solar cells (OSCs) have attracted great attention in terms of power supply in wearable electronic systems. Here, ultrathin and ultra-lightweight OSCs, with a total thickness of less than 3 µm, with excellent mechanical properties in terms of their flexibility and ability to be stretched are demonstrated. A stabilized power conversion efficiency (PCE) of 15.5% and unprecedented power-per-weight of 32.07 W g⁻¹ at a weight of 4.83 g m⁻² is achieved, which represents one of the best-performing OSCs based on ultrathin foils substrate reported to date. The ternary strategy introduces the third component of amorphous conformation of the PC₇₁BM molecule, which can slightly reduce crystallization and aggregates without decreasing the electron mobility, thereby reducing rigidity and brittleness of the active layer. The increase in the ductility of the active layer significantly improves the mechanical flexibility of the device, resulting in over 90% retention in the PCE after 200 stretching–compression cycles. In addition, the ternary device exhibits excellent stability when stored in a N₂-filled glove box, resulting in the PCE retaining over 95% of its initial efficiency even after 1000 h. This ultraflexible and ultra-lightweight photovoltaic foils constitute a major step toward the integration of power supply into malleable electronic textiles.

An alternative pathway to the determination of organic solar cell fill-factor figures of merit, θ and α, expressing them in terms of the effective carrier drift and diffusion lengths is presented. This simplifies their elucidation with the experimental results, covering a range of nonfullerene acceptor-based devices, demonstrating a strong agreement both with the analytical equations and the drift-diffusion simulations.

Abstract

Organic solar cells (OSC) nowadays match their inorganic competitors in terms of current production but lag behind with regards to their open-circuit voltage loss and fill-factor, with state-of-the-art OSCs rarely displaying fill-factor of 80% and above. The fill-factor of transport-limited solar cells, including organic photovoltaic devices, is affected by material and device-specific parameters, whose combination is represented in terms of the established figures of merit, such as θ and α. Herein, it is demonstrated that these figures of merit are closely related to the long-range carrier drift and diffusion lengths. Further, a simple approach is presented to devise these characteristic lengths using steady-state photoconductance measurements. This yields a straightforward way of determining θ and α in complete cells and under operating conditions. This approach is applied to a variety of photovoltaic devices—including the high efficiency nonfullerene acceptor blends—and show that the diffusion length of the free carriers provides a good correlation with the fill-factor. It is, finally, concluded that most state-of-the-art organic solar cells exhibit a sufficiently large drift length to guarantee efficient charge extraction at short circuit, but that they still suffer from too small diffusion lengths of photogenerated carriers limiting their fill factor.

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.

A reliable and accurate efficiency measurement protocol for emerging photovoltaic (PV) technologies is proposed. This protocol does not require any specialized equipment beyond what a PV research laboratory already possesses and is validated on over 200 emerging PV devices received globally, including some record-efficiency cells.

Abstract

Emerging photovoltaic (PV) technologies (e.g., organic, perovskite, and solution processed quantum dot) have attracted remarkable attention with the rapid growth of their efficiencies, and their transition toward commercialization. Accurate and reliable efficiency measurements of these PV technologies are crucial, yet much more complicated than for conventional PV technologies due to the former's pronounced dynamic responses to changes in measurement conditions (e.g., current–voltage (I–V) scan rate and preconditioning) and their susceptibility to degradation. Adjustments to the measurement procedures are therefore necessary so that a reproducible “steady state” is reached during measurement. Furthermore, given the small size of many emerging cells, inappropriate device area definition and solar simulator setup can lead to measurement errors. Here, comprehensive efficiency calibration guidance is offered for emerging solar cells, including area measurement; spectral irradiance translation to standard test conditions; and steady-state electrical performance. The necessity of reporting steady-state efficiency is justified with a statistical performance comparison between conventional and steady-state I–V scans over hundreds of cells the group has received globally for efficiency certifications. The procedures described here do not require specialized measurement instrumentation; what matters most are changes to the measurement protocols. These described changes aim to enable better comparisons between reported efficiencies.

Interfacial engineering of thin interlayers on the surface of a perovskite is shown to be one of the most effective methods for improving the stability of perovskite solar cell (PSCs). Here, a water stable haloplumbate for modulation of PSCs is introduced, which shows an protective effect against water and improves the power conversion efficiency and stability of perovskite solar cells.

Abstract

The commercialization of perovskite solar cells is mainly limited by their operational stability. Interlayer modification by thin interface materials between the perovskite and the charge transport layers is one of the most effective methods to promote the efficiency and stability of perovskite devices. However, the commonly used interlayer materials do not fulfill all the demands, including good film quality, excellent stability, and passivation capability without interfering with the charge transport. In this work, a water stable haloplumbate [TBA]PbI₃ for interfacial modification that meets these demands is proposed, which is formed on the perovskite surface in situ by tetra-butylammonium iodide treatment. Benefiting from its passivation effect and robustness, the modified devices result in a power conversion efficiency of 22.90% with enhanced environmental and operational stability. In addition, the self-limiting effect of the reaction contributes to the controllability of device fabrication and the repeatability of device performance.

Nature Energy, Published online: 25 May 2021; doi:10.1038/s41560-021-00838-1

Publication date: September 2021

Source: Nano Energy, Volume 87

Author(s): Qingling Nie, Ailing Tang, Qiang Guo, Erjun Zhou

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

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.