Chen Weijie

Ge is incorporated for the first time into CsPbI₃-based perovskites. Ge incorporation can modify crystallization growth of CsPb_{1− x} Ge _x I₃ films and passivate grain boundary and interfacial defects. The CsPb_0.95Ge_0.05I₃-based perovskite solar cell (PSC) presents 19.52% efficiency with a certified efficiency of 18.8%. In addition, moisture resistance properties and excellent operational stability are also achieved.

Abstract

Aiming at stable CsPbI₃ perovskite solar cells, Ge incorporated for the first time into DMAPbI₃-based precursor systems. Ge incorporation is found to be able to modify crystallization growth of CsPb_{1− x} Ge _x I₃ films and reduce annealing temperature and treatment time by lowering CsPbI₃ formation energy. The champion power conversion efficiency (PCE) of 19.52% is achieved with a certified PCE of 18.8%, which is the highest performance of CsPbI₃ PSCs with alien element-doping. In addition, in situ formation of GeO₂ can passivate the grain boundary and surface defects, thus significantly improving the moisture resistance of the perovskite film and related devices. Excellent operational stability is achieved with no PCE degradation over 3000 h at a fixed bias voltage of 0.85 V under continuous white LED (6500 K) illumination and a nitrogen atmosphere. This work demonstrates that Ge-incorporation is a promising way to stabilize CsPbI₃ perovskite solar cells by simultaneously improving perovskite crystallinity and passivating the grain boundary and interfacial defects.

The progressive improvement of charge extraction and suppression of charge recombination by side-chain engineering of Y-series nonfullerene acceptors (NFAs), employing a ternary blend and introducing a volatilizable solid additive, fine-tunes the electronic properties of the NFAs and optimizes the morphology of the active layer and contributes to a record power conversion efficiency of 19.05% for single-junction polymer solar cells.

Abstract

Improving charge extraction and suppressing charge recombination are critically important to minimize the loss of absorbed photons and improve the device performance of polymer solar cells (PSCs). In this work, highly efficient PSCs are demonstrated by progressively improving the charge extraction and suppressing the charge recombination through the combination of side-chain engineering of new nonfullerene acceptors (NFAs), adopting ternary blends, and introducing volatilizable solid additives. The 2D side chains on BTP-Th induce a certain steric hindrance for molecular packing and phase separation, which is mitigated by fluorination of side chains on BTP-FTh. Moreover, by introducing two highly crystalline molecules as the second acceptor and volatilizable solid additive, respectively, into the BTP-FTh-based host blend, the molecular crystallinity is significantly improved and the blend morphology is finely optimized. As expected, enhanced charge extraction and suppressed charge recombination are progressively realized, contributing to the largely improved fill factor (FF) of the resultant devices. Accompanied by the enhanced open-circuit voltage (V _oc) and short-circuit current density (J _sc), a record high power conversion efficiency (PCE) of 19.05% is realized finally.

A facile, universal, and ecofriendly approach is reported for the synthesis of the 2D-layered perovskites at room temperature. Potassium ions can assist both the crystal growth and surface passivation, improving stability and passivated trap states.

2D hybrid halide-layered perovskites have been compelling candidates for photovoltaics and optoelectronics owing to their remarkable electrical and optical properties. However, high-quality crystals are usually obtained either through complicated and energy-consuming procedures or using toxic solvents, which remains a significant challenge to the crystal synthesis. To address the issue, a facile, universal, ecofriendly, and energy-saving approach to synthesize the Ruddlesden−Popper- and Dion−Jacobson-phase 2D-layered potassium-passivated perovskites at room temperature is reported. By involving potassium iodide to the reaction, potassium ions can assist both the crystal growth and surface passivation, improving their stability and passivated trap states. Potassium-passivated (R-MBA)₂PbI₄ exhibits superior optoelectronic features than pristine (R-MBA)₂PbI₄ as well as outstanding strain stability. The findings herein may not only improve synthetic methods to obtain high-quality crystals, but also motivate more fundamental investigations for potential optoelectronic and flexible applications.

Raman spectroscopy is used to compare the anharmonic expressions in the structural dynamics of two halide perovskites. In Cs₂AgBiBr₆, clear normal modes are observed in all measured temperatures. Contrary to this, the Raman spectrum of CsPbBr₃ exhibits a breakdown of the normal-mode picture above 200 K. Implications of these diverging behaviors on the electronic properties of the crystals is discussed.

Abstract

Lead-based halide perovskite crystals are shown to have strongly anharmonic structural dynamics. This behavior is important because it may be the origin of their exceptional photovoltaic properties. The double perovskite, Cs₂AgBiBr₆, has been recently studied as a lead-free alternative for optoelectronic applications. However, it does not exhibit the excellent photovoltaic activity of the lead-based halide perovskites. Therefore, to explore the correlation between the anharmonic structural dynamics and optoelectronic properties in lead-based halide perovskites, the structural dynamics of Cs₂AgBiBr₆ are investigated and are compared to its lead-based analog, CsPbBr₃. Using temperature-dependent Raman measurements, it is found that both materials are indeed strongly anharmonic. Nonetheless, the expression of their anharmonic behavior is markedly different. Cs₂AgBiBr₆ has well-defined normal modes throughout the measured temperature range, while CsPbBr₃ exhibits a complete breakdown of the normal-mode picture above 200 K. It is suggested that the breakdown of the normal-mode picture implies that the average crystal structure may not be a proper starting point to understand the electronic properties of the crystal. In addition to our main findings, an unreported phase of Cs₂AgBiBr₆ is also discovered below ≈37 K.

Publication date: May 2022

Source: Nano Energy, Volume 95

Author(s): Hang Su, Lu Zhang, Yucheng Liu, Yingjie Hu, Bobo Zhang, Jiaxue You, Xinyi Du, Jing Zhang, Xiaodong Ren, Jing Gou, Shengzhong (Frank) Liu

Conjugated mesopolymer is first applied in non-fullerene solar cells. The champion device based on MePBDFCl _H /Y6 shows a power conversion efficiency (PCE) of 15.06%, which is attributed to the efficient intermolecular charge transfer. Meanwhile, the champion PCE is a new record for benzo[1,2-b:4,5-b′]difuran-based organic solar cells. More importantly, the batch-to-batch variation is effectively reduced by adopting mesopolymer.

Abstract

The high-performance organic solar cells (OSCs) tend to choose the polymers with high molecular weight as donors, which easily produce good crystallinity to facilitate intermolecular charge transfer. However, these polymers usually accompanied by the low solubility and synthetic difficulty, increasing batch-to-batch variations. The proposal of conjugated mesopolymers (molar mass (M _n) in 1–10 kDa) can overcome these problems. Herein, a new mesopolymer, MePBDFCl _H as donor material is designed and synthesized, and firstly applied in OSCs. As a comparison, other lower molecular weight mesopolymer of MePBDFCl _L and higher molecular weight polymer of PBDFCl with same structure are also prepared and investigated. Because of its appropriate phase separation and miscibility in the blend film, the MePBDFCl _H exhibits the highest power conversion efficiency (PCE) of 15.06% among the three materials. Meanwhile, the champion PCE is a new record for benzo[1,2-b:4,5-b′]difuran-based photovoltaic materials. Importantly, comparing to the pronounced PCE decrease of polymer PBDFCl by about 12%, a slightly PCE difference for mespolymer MePBDFCl _L is only less than 5%, reducing the batch-to-batch variation. This work not only suggests that the benzo[1,2-b:4,5-b′]difuran unit is a promising electron-donating core but also shows that the mesopolymers have great potentials to produce the low-differentiated and high-performance organic photovoltaic materials.

High-performance organic solar cells (OSCs) based on D18-Cl and N3 are fabricated by combining volatile solid additive 1,4-diiodobenzene (DIB) with sequential deposition (SD) strategy. The formed D18-Cl/N3(DIB) film exhibits favorable phase separation and enhanced crystallinity. The optimized morphology enables a remarkable power conversion efficiency of 18.42%, which is one of the highest performances in binary SD OSCs to date.

Abstract

Morphology optimization of active layer plays a critical role in improving the performance of organic solar cells (OSCs). In this work, a volatile solid additive-assisted sequential deposition (SD) strategy is reported to regulate the molecular order and phase separation in solid state. The OSC adopts polymer donor D18-Cl and acceptor N3 as active layer, as well as 1,4-diiodobenzene (DIB) as volatile additive. Compared to the D18-Cl:N3 (one-time deposition of mixture) and D18-Cl/N3 (SD) platforms, the D18-Cl/N3(DIB) device based on DIB-assisted SD method exhibits a finer phase separation with greatly enhanced molecular crystallinity. The optimal morphology delivers superior charge transport and extraction, offering a champion power conversion efficiency of 18.42% with significantly enhanced short-circuit current density (J _sc) of 27.18 mA cm⁻² and fill factor of 78.8%. This is one of the best performances in binary SD OSCs to date. Angle-dependent grazing-incidence wide-angle X-ray scattering technique effectively reveals the vertical phase separation and molecular crystallinity of the active layer. This work demonstrates the combination of volatile solid additive and sequential deposition is an effective method to develop high-performance OSCs.

The guanidinium (GA) cation, acetate (Ac) anion and glycocyamine (GCA) are respectively employed as a dopant, nucleating agent and additive into the CsPbTh3 (Th=I, Br, Cl) perovskite. With this combinational strategy, the CsPbTh3 perovskite solar cell exhibits improved phase stability, lower trap-assisted recombination and better energy-level match, resulting in not only higher efficiency of 19.37% but also better ambient stability.

Abstract

The distorted lead iodide octahedra of all-inorganic perovskite based on triple halide-mixed CsPb(I_2.85Br_0.149Cl_0.001) framework have made a tremendous breakthrough in its black phase stability and photovoltaic efficiency. However, their performance still suffers from severe ion migration, trap-induced nonradiative recombination, and black phase instability due to lower tolerance factor and high total energy. Here, a combinational passivation strategy to suppress ion migration and reduce traps both on the surface and in the bulk of the CsPhTh₃ perovskite film is developed, resulting in improved power conversion efficiency (PCE) to as high as 19.37%. The involvement of guanidinium (GA) into the CsPhTh₃ perovskite bulk film and glycocyamine (GCA) passivation on the perovskite surface and grain boundary synergistically enlarge the tolerance factor and suppress the trap state density. In addition, the acetate anion as a nucleating agent significantly improves the thermodynamic stability of GA-doped CsPbTh₃ film through the slight distortion of PbI₆ octahedra. The decreased nonradiative recombination loss translates to a high fill factor of 82.1% and open-circuit voltage (V _OC) of 1.17 V. Furthermore, bare CsPbTh₃ perovskite solar cells without any encapsulation retain 80% of its initial PCE value after being stored for one month under ambient conditions.

Thermally activated delayed fluorophores are constructed with strong through-space donor–acceptor interactions by minimizing their face-to-face distance of 2.7–2.8 Å, realizing efficient blue emission and fast radiative decay. The materials show maximum external quantum efficiencies of 27.8 % and 34.7 % with relieved efficiency roll-off and CIE _y coordinates of 0.29 and 0.15, when used as emitter and sensitizer in organic light-emitting diodes.

Abstract

Thermally activated delayed fluorophors (TADF) featuring through-space charge transfers (TSCT) suffer from low radiative decay rates (k _rs), especially for blue emitters. Here, a xanthene bridge is adopted to construct space-confined face-to-face donor–acceptor alignment and minimize their distances down to 2.7–2.8 Å, even shorter than the interlayer distance of graphite and thus strengthening the electronic interactions. The resulting blue TSCT-TADF emitters exhibit peaks around ≈460 nm, photoluminescence quantum yields of >90 %, and k _rs of nearly 10⁷ s⁻¹, almost 2–10 times higher than previously observed values with comparable reverse intersystem crossing rates. The corresponding blue organic light-emitting diodes show maximum external quantum efficiencies of 27.8 % and 34.7 % with Commission Internationale de L'Eclairage y coordinates of 0.29 and 0.15 using those molecules as emitters and sensitizers, respectively.

An interfacial chemistry strategy is developed to dramatically increase radiative recombination of perovskites. The oxide-bonded perovskite has a large exciton binding energy and a high localized density of electronic state, exhibiting an unprecedented 5000 fold increase in the radiative recombination rate. The enormously enhanced radiative recombination promises to significantly promote the perovskite optoelectronic performance.

Abstract

Efficient radiative recombination is essential for perovskite luminescence, but the intrinsic radiative recombination rate as a basic material property is challenging to tailor. Here we report an interfacial chemistry strategy to dramatically increase the radiative recombination rate of perovskites. By coating aluminum oxide on the lead halide perovskite, lead–oxygen bonds are formed at the perovskite-oxide interface, producing the perovskite surface states with a large exciton binding energy and a high localized density of electronic state. The oxide-bonded perovskite exhibits a ≈500 fold enhanced photoluminescence with a ≈10 fold reduced lifetime, indicating an unprecedented ≈5000 fold increase in the radiative recombination rate. The enormously enhanced radiative recombination promises to significantly promote the perovskite optoelectronic performance.