shenyunxiu

A quaternary strategy is used to achieve desirable carrier behaviors and optimized multiphase morphology; thus, the device shows an outstanding power conversion efficiency (PCE) of 19.32% (certified 19.35%). Furthermore, the device with ≈300 nm-thick film shows a high efficiency of 17.55%, and the large-area devices (1.05 and 72.25 cm²) deliver encouraging PCEs of 18.25% and 12.20%, which are among the highest values reported so far.

Abstract

With the continuous breakthrough of the efficiency of organic photovoltaics (OPVs), their practical applications are on the agenda. However, the thickness tolerance and upscaling in recently reported high-efficiency devices remains challenging. In this work, the multiphase morphology and desired carrier behaviors are realized by utilizing a quaternary strategy. Notably, the exciton separation, carrier mobility, and carrier lifetime are enhanced significantly, the carrier recombination and the energy loss (E _loss) are reduced, thus beneficial for a higher short-circuit density (J _SC), fill factor (FF), and open-circuit voltage (V _OC) of the quaternary system. Moreover, the intermixing-phase size is optimized, which is favorable for constructing the thick-film and large-area devices. Finally, the device with a 110 nm-thick active layer shows an outstanding power conversion efficiency (PCE) of 19.32% (certified 19.35%). Furthermore, the large-area (1.05 and 72.25 cm²) devices with 110 nm thickness present PCEs of 18.25% and 12.20%, and the device with a 305 nm-thick film (0.0473 cm²) delivers a PCE of 17.55%, which are among the highest values reported. The work demonstrates the potential of the quaternary strategy for large-area and thick-film OPVs and promotes the practical application of OPVs in the future.

Publication date: 16 February 2022

Source: Joule, Volume 6, Issue 2

Author(s): Wei Meng, Kaicheng Zhang, Andres Osvet, Jiyun Zhang, Wolfgang Gruber, Karen Forberich, Bernd Meyer, Wolfgang Heiss, Tobias Unruh, Ning Li, Christoph J. Brabec

The dominant deep defect states in freshly prepared CsPbI_{3− x} Br _x films are mainly antisite defect pairs (Pb_I and I_Pb) and interstitial defects (Pb_i). All these defects are reduced because of self-regulation process after resting the films overnight in the dark. Based on this strategy, the reduced-defect high quality CsPbI_{3− x} Br _x films can be obtained and thus higher photovoltaic performance.

Abstract

Deep defects often act as Shockley–Read–Hall recombination centers in semiconductor materials, degrading the photoelectric performance and long-term stability of assembled photovoltaic devices. In this report, deep level transient spectroscopy is probed to determine defect concentrations and defect energy levels in all-inorganic CsPbI_{3− x} Br _x perovskite solar cells. Combining that data with the density functional theory calculation, the dominant deep defect states are assigned to antisite defect pairs (Pb_I and I_Pb) and interstitial defects (Pb_i) in freshly prepared CsPbI_{3− x} Br _x films. Astonishingly, all these defects are reduced by approximately one or two orders of magnitude after resting the films overnight, in excellent agreement with the defect-reduced trends from the fluorescence spectra, transient photovoltage, and space-charge-limited current measurements. The reduced defect concentrations are proposed to be connected with their self-regulation during the storage. To assess the thermodynamics possibilities, two reaction procedures are designed to calculate their formation enthalpies and negative Gibbs energy change revealed their spontaneous processes. Then, strain relief is the direct driving force for ion migration, thus defect-regulation by tracing the X-ray diffraction patterns. Furthermore, the power conversion efficiency is improved and the J–V hysteresis is suppressed due to reduced ion migration via relaxed strain.

A highly phase‐stable perovskite film without the methylammonium cation is fabricated by introducing cesium chloride in the double cation Cs, formamidinium perovskite precursor, leading to high power conversion efficiency of 20.5% and remarkable long‐term stability. The unencapsulated perovskite solar cell retains about 80% of its initial efficiency after a 1000 h aging study, demonstrating a feasible approach to enhance solar cell efficiency and stability simultaneously.

Abstract

Organic–inorganic metal halide perovskite solar cells (PSCs) have achieved certified power conversion efficiency (PCE) of 25.2% with complex compositional and bandgap engineering. However, the thermal instability of methylammonium (MA) cation can cause the degradation of the perovskite film, remaining a risk for the long‐term stability of the devices. Herein, a unique method is demonstrated to fabricate highly phase‐stable perovskite film without MA by introducing cesium chloride (CsCl) in the double cation (Cs, formamidinium) perovskite precursor. Moreover, due to the suboptimal bandgap of bromide (Br⁻), the amount of Br⁻ is regulated, leading to high power conversion efficiency. As a result, MA‐free perovskite solar cells achieve remarkable long‐term stability and a PCE of 20.50%, which is one of the best results for MA‐free PSCs. Moreover, the unencapsulated device retains about 80% of the original efficiencies after a 1000 h aging study. These results provide a feasible approach to enhance solar cell stability and performance simultaneously, paving the way for commercializing PSCs.

In article number https://doi.org/10.1002/adma.2019036491903649, Xiaotian Hu, Wei Ma, Yiwang Chen, and co‐workers report a general approach to upscale flexible organic photovoltaics to the module scale without obvious efficiency loss by calculating the shear impulse during the coating/printing process. Photoelectric conversion efficiencies of 9.77% for a 1 cm² single chip and 8.90% for a 15 cm² solar module are demonstrated. The mechanics of shear impulse link the spin‐coating and slot‐die printing like a small boat overcoming the obstacles of thousands of mountains to arrive at a large‐area printing ferry. This research method also opens up a new strategy of lab‐to‐manufacturing translation for organic optoelectronic devices.

A 0D Cs₄PbI₆/3D CsPbI₃ heterostructure is achieved by tuning the stoichiometry of the precursors. The coexistent Cs₄PbI₆ not only reduces the grain size of the CsPbI₃ and serves as a molecular lock to stabilize the black‐phase CsPbI₃, but also passivates the defects in the grain boundaries and improves the surface coverage to improve the device performance to 16.39%.

Abstract

Although organic–inorganic hybrid perovskite solar cells (PVSCs) have achieved dramatic improvement in device efficiency, their long‐term stability remains a major concern prior to commercialization. To address this issue, extensive research efforts are dedicated to exploiting all‐inorganic PVSCs by using cesium (Cs)‐based perovskite materials, such as α‐CsPbI₃. However, the black‐phase CsPbI₃ (cubic α‐CsPbI₃ and orthorhombic γ‐CsPbI₃ phases) is not stable at room temperature, and it tends to convert to the nonperovskite δ‐CsPbI₃ phase. Here, a simple yet effective approach is described to prepare stable black‐phase CsPbI₃ by forming a heterostructure comprising 0D Cs₄PbI₆ and γ‐CsPbI₃ through tuning the stoichiometry of the precursors between CsI and PbI. Such heterostructure is manifested to enable the realization of a stable all‐inorganic PVSC with a high power conversion efficiency of 16.39%. This work provides a new perspective for developing high‐performance and stable all‐inorganic PVSCs.