Chen Weijie

A new method is developed to synthesize SnO _x ‐Cl colloids and to realize an in situ and spontaneous ion‐exchange reaction during the perovskite film crystallization process. It is found that such ion exchange can perfectly passivate the interface defects and reduce energy loss at the interface.

Abstract

Interface engineering is of great concern in photovoltaic devices. For the solution‐processed perovskite solar cells, the modification of the bottom surface of the perovskite layer is a challenge due to solvent incompatibility. Herein, a Cl‐containing tin‐based electron transport layer; SnO _x ‐Cl, is designed to realize an in situ, spontaneous ion‐exchange reaction at the interface of SnO _x ‐Cl/MAPbI₃. The interfacial ion rearrangement not only effectively passivates the physical contact defects, but, at the same time, the diffusion of Cl ions in the perovskite film also causes longitudinal grain growth and further reduces the grain boundary density. As a result, an efficiency of 20.32% is achieved with an extremely high open‐circuit voltage of 1.19 V. This versatile design of the underlying carrier transport layer provides a new way to improve the performance of perovskite solar cells and other optoelectronic devices.

The studies from the steady‐state and time‐dependent measurements indicate that the extended absorption range, short charge carrier extraction time, and high charge carrier mobility by the non‐fullerene electron acceptors in the photoactive layer are responsible for enhanced photocurrent in ternary organic solar cells.

Ternary organic solar cells, a single active layer comprising three different components, are demonstrated to be one of the most efficient ways to approach high‐performance organic solar cells. But nevertheless, most of the ternary organic solar cells are characterized by steady‐state measurements, which are helpful but inadequate to fully understand the underlying charge carrier behavior at a short time scale. Herein, a comparison of the steady‐state and time‐dependent measurements is used to investigate the functionality of non‐fullerene electron acceptors in ternary organic solar cells. The steady‐state measurements indicate that non‐fullerene electron acceptors enlarge the absorption range of the photoactive layer, suppress charge carrier recombination, reduce charge carrier transfer resistance, and thereby increase photocurrent in ternary organic solar cells. The time‐dependent measurements demonstrate that a short charge carrier extraction time and a high charge carrier mobility are responsible for enhanced photocurrent in ternary organic solar cells. A comprehensive method understanding the underlying of enhanced efficiency of ternary organic solar cells is provided herein.

Publication date: 18 September 2019

Source: Joule, Volume 3, Issue 9

Author(s): Henk J. Bolink

Ag nanorods aqueous solution is introduced to the perovskite absorber layer to enhance the power conversion efficiency from 18.5% to 20.29%, with fill factors close to 82%. Ag nanorods increase light absorption by the local surface plasmon resonance effect, and the presence of water leads to high‐quality perovskite films by inducing recrystallization.

Perovskite solar cells (PSCs) have been widely studied during the past 10 years. Albeit the excellent light‐absorption ability, the thickness of the perovskite layer is limited to maintain effective control over morphology and carrier migration. Meanwhile, the quality of perovskite films is a crucial factor affecting the performance of final devices. The traditional one‐step process for preparing triple‐cation perovskite films suffers from small grain size, low crystallization quality, and many surface defects. Herein, in the process of triple‐cation perovskite‐based solar cells, a facile dosing strategy of a silver nanorods (AgNR) aqueous solution into the perovskite precursor is adopted. The localized surface plasmon resonance effect of AgNR enhances the light‐capture ability of the perovskite layer without increasing the thickness. At the same time, the presence of appropriate water helps to obtain high‐quality perovskite films with larger grain size and fewer defects. It is found that the synergy of AgNR and water successfully reduces the defect density and increases mobility significantly. Consequently, a power conversion efficiency of 20.18% and a short‐circuit current (J _SC) of 22.08 mA cm⁻² is achieved. Meanwhile, an excellent fill factor beyond 82% is reported, which is one of the highest values for triple‐cation hybrid PSCs.

Progress in the development of expitaxial two‐terminal GaInP/GaAs/Si triple‐junction solar cells is reported. By reducing the defect density in the metamorphic III–V layers to a value of 2.2 × 10⁷ cm⁻², the conversion efficiency is increased from 19.7% to 22.3% under AM1.5g conditions. A detailed characterization of the device is provided to identify the main loss mechanisms.

III–V on Si multijunction solar cells exceede the efficiency limit of Si single‐junction devices but are often challenged by expensive layer transfer techniques. Here, progress in the development of direct epitaxial growth for GaInP/GaAs/Si triple‐junction solar cells is reported. III–V absorbers with a total thickness of 4.9 μm are grown onto a Si bottom cell using metal organic vapor phase epitaxy. A new record efficiency of 22.3% under AM1.5g conditions is reached herein, outperforming the previous value of 19.7%. This improvement is possible through better nucleation conditions for the first GaP layer on Si and consequently the reduction of threading dislocations within the III–V absorbers from 1.4 × 10⁸ to 2.2 × 10⁷ cm⁻². Further efficiency improvements toward 30% require even lower threading dislocation densities in the order of 1 × 10⁶ cm⁻², better light trapping in the Si bottom cell, and a reduction of parasitic absorption within the GaAs _y P_1–y graded buffer.

This study presents a reasonable strategy for designing 2DBDT‐chlorinated thiophene‐based donor polymers with balanced molecular weight and solubility by modifying the structure of previously reported low cost P(Cl) to achieve high‐efficiency polymer solar cells (PSCs). As a result, the new P(Cl–Cl)(BDD = 0.2) reaches a high power conversion efficiency of 13.9% using eco‐friendly solvents for commercialization of PSCs.

Abstract

To industrialize nonfullerene polymer solar cells (NFPSCs), the molecular design of the donor polymers must feature low‐cost materials and a high overall yield. Two chlorinated thiophene‐based polymers, P(F–Cl) and P(Cl–Cl), are synthesized by introducing halogen effects like fluorine (F) and chlorine (Cl) to the previously reported P(Cl), which exhibits low complexity. However, the molecular weights of these polymers are insufficient owing to their low solubility, which in turn is caused by introducing rigid halogen atoms during the polymerization. Thus, they show relatively low power conversion efficiencies (PCEs) of 11.8% and 10.3%, respectively. To overcome these shortcomings, two new terpolymers are designed and synthesized by introducing a small amount of 1,3‐bis(5‐bromothiophen‐2‐yl)‐5,7‐bis(2‐ethylhexyl)benzo[1,2‐c:4,5‐c′]dithiophene‐4,8‐dione (BDD) unit into each backbone, namely, P(F–Cl)(BDD = 0.2) and P(Cl–Cl)(BDD = 0.2). As a result, both polymers remain inexpensive and show a better molecular weight–solubility balance, achieving high PCEs of 12.7% and 13.9%, respectively, in NFPSCs processed using eco‐friendly solvents.

Hybrid halide perovskites and ferroelectric perovskites are two different classes of materials with analogies in their structure. Such analogies and state‐of‐the‐art technologies based on these materials are reviewed so that future multisource energy conversion devices (which are capable of utilizing piezoelectric, pyroelectric, photovoltaic, and thermoelectric effects simultaneously) and storage devices can be created in a holistic manner.

Abstract

An insight into the analogies, state‐of‐the‐art technologies, concepts, and prospects under the umbrella of perovskite materials (both inorganic–organic hybrid halide perovskites and ferroelectric perovskites) for future multifunctional energy conversion and storage devices is provided. Often, these are considered entirely different branches of research; however, considering them simultaneously and holistically can provide several new opportunities. Recent advancements have highlighted the potential of hybrid perovskites for high‐efficiency solar cells. The intrinsic polar properties of these materials, including the potential for ferroelectricity, provide additional possibilities for simultaneously exploiting several energy conversion mechanisms such as the piezoelectric, pyroelectric, and thermoelectric effect and electrical energy storage. The presence of these phenomena can support the performance of perovskite solar cells. The energy conversion using these effects (piezo‐, pyro‐, and thermoelectric effect) can also be enhanced by a change in the light intensity. Thus, there lies a range of possibilities for tuning the structural, electronic, optical, and magnetic properties of perovskites to simultaneously harvest energy using more than one mechanism to realize an improved efficiency. This requires a basic understanding of concepts, mechanisms, corresponding material properties, and the underlying physics involved with these effects.

Publication date: November 2019

Source: Nano Energy, Volume 65

Author(s): Van-Dang Tran, S.V.N. Pammi, Byeong-Ju Park, Yire Han, Cheolho Jeon, Soon-Gil Yoon

Graphical abstract

Publication date: November 2019

Source: Nano Energy, Volume 65

Author(s): Peng Zhai, Tzu-Sen Su, Tsung-Yu Hsieh, Wei-Yen Wang, Lixia Ren, Jiayi Guo, Tzu-Chien Wei

Graphical abstract

Herein, a facile strategy that can carry out double passivation to improve the performance of perovskite solar cells (PSCs) is demonstrated. By using the dilute halide salt PEABr solution to treat the perovskite film, PbI₂ can precipitate from the perovskite. Both PEABr and PbI₂ can passivate the perovskite film; double passivation improves the performance of PSCs significantly.

Material passivation is essential to enhance the quality of perovskite materials and boost the performance of perovskite solar cells (PSCs). However, most of the previous reports only paid attention to improving the quality of perovskite films by adopting single passivation. Here, a facile strategy that can carry out double passivation to improve the performance of PSCs is demonstrated. By using the dilute halide salt PEABr solution to treat the perovskite film, PbI₂ can precipitate from the perovskite. Both PEABr and PbI₂ can passivate the perovskite film, and by combining PEABr and PbI₂, the double passivation improves the performance of PSCs significantly. Very high short‐circuit current density of 24.30 mA cm⁻², open‐circuit voltage of 1.10 V, and fill factor of 79.75% are achieved which lead to a surprising efficiency of 21.32% for the passivated device. The improved efficiency is mainly according to the available surface passivation of the perovskite material, leading to repressed nonradiative recombination and unhindered charge collection. In addition, the passivated device exhibits better power conversion efficiency stability relative to the control device.

A power conversion efficiency of 13.36% in ternary organic photovoltaics is obtained by carefully picking materials with good compatibility and complementary absorption spectra, as well as well‐matched energy levels with efficient energy transfer.

Abstract

Organic photovoltaics (OPVs) are fabricated with PM6 as donor and T6Me, IT‐2F, or their mixture as acceptor. A 13.36% power conversion efficiency (PCE) is achieved from the optimized ternary OPVs with 50 wt% IT‐2F in acceptors, which is attributed to the enhanced photon harvesting of ternary active layers and improved exciton utilization efficiency through energy transfer from IT‐2F to T6Me. The efficient energy transfer from IT‐2F to T6Me can be confirmed from the photoluminescence spectra of neat and blend films, which may provide additional channels to enhance exciton utilization efficiency for achieving short‐circuit current density (J _SC) improvement of ternary OPVs. It should be highlighted that the fill factor (FF) of ternary OPVs can be monotonously increased along with the incorporation of IT‐2F, indicating the gradually optimized phase separation degree of ternary active layers. The third component IT‐2F plays a key role in optimizing phase separation as a morphology regulator. Over 8% PCE improvement is achieved in the optimized ternary OPVs compared with the over 12% PCEs of the corresponding binary OPVs, respectively. This work indicates that the performance of ternary OPVs can be well optimized by carefully picking materials with good compatibility and complementary absorption spectra, as well as the appropriate energy levels.