Zhang Zelong

Decay times of measured transient photoluminescence (TPL) and transient photovoltage (TPV) are both used to study recombination in halide perovskites but the decay times often differ substantially. Here, a consistent approach to interpret the decays is presented that allows the different parts of the optical and electrical transients to be correctly interpreted, and explains how they are related to material properties.

Abstract

Transient photoluminescence (TPL) and transient photovoltage (TPV) measurements are important and frequently applied methods to study recombination dynamics and charge-carrier lifetimes in the field of halide-perovskite photovoltaics. However, large-signal TPL and small-signal TPV decay times often correlate poorly and differ by orders of magnitude. In order to generate a quantitative understanding of the differences and similarities between the two methods, the impact of sample type (film vs device), large- versus small-signal analysis, and differences in detection mode (voltage vs. luminescence) are explained using analytical and numerical models compared with experimental data. The main solution to achieving a consistent framework that describes both methods is the calculation of a voltage or carrier density dependent decay time that can be interpreted in terms of a capacitive region, a region dominated by defect-assisted recombination and a region that is dominated by higher order recombination (radiative and Auger). It is experimentally shown that in the efficient methylammonium lead-iodide solar cells, effective monomolecular lifetimes ≈2 µs can be consistently measured with TPL and TPV. Furthermore, the shape of the decay time versus voltage or carrier density follows predictions derived from implicit and explicit solutions to differential equations.

Nature, Published online: 20 October 2021; doi:10.1038/s41586-021-03964-8

Electro-strictive strain in 3D polycrystalline perovskite is observed, which can lead to an accelerated ion migration under operational conditions. The 1D–3D perovskite, that is, 1D BnPbI₃ perovskite, spatially distributed in the 3D perovskite film and compensating the dangling bonds in the grain boundaries, can effectively inhibit electro-strictive responses and unbalanced charge carrier extraction, realizing ultralong operational stability.

Abstract

3D organic–inorganic hybrid halide perovskite solar cells (pero-SCs) inherently face severe instability issue due to ion migration under operational conditions. This ion migration inevitably results from the decomposition of ionic bonds under lattice strain and is accelerated by the existence of excess charge carriers. In this study, a 1D–3D mixed-dimensional perovskite material is explored by adding an organic salt with a bulk benzimidazole cation (Bn⁺). The Bn⁺ can induce 3D perovskite crystalline growth with the preferred orientation and form a 1D BnPbI₃ perovskite spatially distributed in the 3D perovskite film. For the first time, the electro-strictive response, which has a significant influence on the lattice strain under an electric field, is observed in polycrystalline perovskite. The 1D–3D perovskite can effectively suppress electro-strictive responses and unbalanced charge carrier extraction, providing an intrinsically stable lattice with enhanced ionic bonds and fewer excess charge carriers. As a result, the ion migration behavior of the p-i-n 1D–3D based pero-SC is dramatically suppressed under operational conditions, showing ultra-long-term stability that retains 95.3% of its initial power conversion efficiency (PCE) under operation for 3072 h, and simultaneously achieving an excellent PCE with a hysteresis-free photovoltaic behavior.

High-quality (FA_0.83MA_0.17)_0.95Cs_0.05Pb(I₀.₈₃Br_0.17)₃ perovskite films are fabricated by solvent volatilization. This method does not need an antisolvent technique and presents significant potential for large-scale and large-area device fabrication. A high power conversion efficiency of 20.6% is obtained by the films. A large area perovskite film of 10 × 10 cm² can be fabricated by the method.

Perovskite solar cells (PSCs) have attracted significant research efforts due to their remarkable performance. However, most perovskite films are prepared by the antisolvent method which is not suitable for practical applications. Herein, a (FA_0.83MA_0.17)_0.95Cs_0.05Pb(I_0.83Br_0.17)₃ (CsFAMA) perovskite film fabrication technique is developed using solvent volatilization without any antisolvents. The films are formed through recrystallization via the intermediate phase CsMAFAPbI _x Cl _y Br _z during annealing, leading to high-quality perovskite films. The perovskite growth mechanism is investigated in terms of controlling the amount of formamidinium iodide and methylammonium chloride in the precursor solutions. The oriental growth of the films via the intermediate phase is confirmed by the grazing-incidence wide-angle X-ray scattering measurements. The photovoltaic properties of the perovskite films are investigated. The PSCs based on the films fabricated using the method exhibit a high efficiency of 20.6%. The method developed in this work is based on solvent volatilization, which exhibits significant potential in high reproducibility, facile operation, and large-scale production.

Self-polymerized monomer 2-(dimethylamino) ethyl methacrylate (DMAEMA) is incorporated into perovskite films by the antisolvent additive engineering, attributing to uniform composition distribution, improved crystallinity, and phase stability. Meanwhile, the defects density and recombination is reduced due to the strong interactions with DMAEMA. Finally, the high performance and stability perovskite solar cells are achieved.

Abstract

While there is promising achievement in terms of the power conversion efficiency (PCE) of perovskite solar cells (PSCs), long-term stability has been considered the main obstacle for their practical application. In this work, the authors demonstrate the small monomer 2-(dimethylamino) ethyl methacrylate (DMAEMA) with unsaturated carboxylic acid ester bond in the antisolvent for perovskite formation to improve the PCE and stability. The results show that DMAEMA is self-polymerized and uniformly distributed in the film, contributing to the improved crystallinity of the perovskites. Equally important, it is found that there are newly established interactions of Pb²⁺ and DMAEMA, and iodine and ternary amine between DMAEMA and perovskites, which improves the uniformity of the lead (II) iodide vertical distribution along with the films and thus phase stability, as well as largely decreases defects density in the film. Overall, the inverted PSCs with DMAEMA exhibit a open-circuit voltage of 1.10 V, short-circuit current of 23.86 mA cm⁻², fill factor of 0.82, and finally PCE reaches 21.52%. Meanwhile, the PSC stability is significantly improved due to the inhibition of the formation of iodine, reduction of the uncoordinated Pb²⁺, and suppression of phase segregation.

To understand the nature of hysteresis, theoretical mechanisms and experimental measurements are provided based on a combination of first-principles simulations, cross-section scanning electron microscopy images, and time-dependent photocurrent measurements. The defect assistance ion-migration process could be the primary contribution to hysteresis. The defect density is reduced via the in situ passivation of PbI₂ crystals, which prevents the migration of ions effectively, and the hysteresis index is decreased from 22.43% to 1.04%.

Abstract

As one of the most promising photovoltaic materials, the efficiency of inorganic–organic hybrid halide perovskite solar cells (PSCs) has reached 25.5% in 2020. However, the stability and hysteresis remain primary challenges before it can become a commercial photovoltaic technology. Therefore, those issues have drawn significant attention for photovoltaic applications. In this work, a study of the PSCs hysteresis improvement is presented based on a combination of first-principles simulations, scanning electron microscopy images, and time-dependent photocurrent measurements. It indicates the hysteresis led by the ion migration and accumulation is mainly localized at the two interfaces: one is between electron transport layer and active layer, and the other is between active layer and hole transport layer. Considering the massive defects at the grain boundaries (GBs), they lower the potential barriers significantly. The defect density at GBs is therefore reduced via the in situ passivation of PbI₂ crystals. The hysteresis index is decreased from 22.43% down to 1.04%, and results in an improvement in efficiency from 17.12% up to 20.10%. Following the understanding of defect-induced hysteresis, an approach to improve the hysteresis is provided, which can be integrated into the fabrication process and widely applied to enhance the performance of PSCs.

The electron transport layer (ETL) plays a crucial part in extracting electrons and optimizing interfacial contact for perovskite solar cells (PVSCs). Herein, the EVA is introduced into PC₆₁BM to promote the orderly molecular stacking of ETLs. The PC₆₁BM:EVA-based MAPbI₃ PVSCs deliver a champion efficiency of 19.32% and regain 80% of initial efficiency after storage under 52% humidity for 1500 h.

Abstract

The electron transport layer (ETL) plays a crucial part in extracting electron carriers while optimizing the interfacial contact of perovskite/electrode in planar heterojunction perovskite solar cells (PVSCs). Despite various ETLs being designed for efficient PVSCs, there exists hardly any research on the effect of molecular stacking order on device performance. Herein, poly(ethylene-co-vinyl acetate) (EVA) is employed as the [6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM) solution additive. The strong binding energy between EVA with PC₆₁BM promotes the molecular stacking order of ETLs, which alleviates the morphology inhomogeneity, possesses a matched energy level, blocks ion migration, and improves the water–oxygen barrier of perovskite devices. The blade-coated MAPbI₃-based PVSCs achieve a power conversion efficiency (PCE) of 19.32% with positive reproducibility and negligible hysteresis, as well as maintain 90% and 80% of the initial PCE after storage under inert and ambient conditions (52% humidity) for 1500 h without encapsulation. This strategy also improves the champion PCE of CsFAMA-based PVSCs to 20.33%. These findings demonstrate that the regulation of molecular stacking order is a valid approach to optimize interfacial charge-carrier recombination in PVSCs, which meet the demand for high-performance ETL in large-area PVSCs and improve the upscaling of the fabrication technology toward practical applications.

This study introduces an octyl-diammonium lead iodide (ODAPbI₄) interlayer onto the hole-transporting layer, which significantly reduces nonradiative recombination of wide-bandgap perovskite devices, enhancing the efficiency of wide-bandgap devices beyond 21%. By coupling a semitransparent device with a Cu₂ZnSn(S,Se)₄ (CZTSSe) cell, a four terminal perovskite/CZTSSe tandem cell with a power conversion efficiency of 22.27% is achieved.

Abstract

Wide-bandgap perovskites have attracted substantial attention due to their important role in serving as a top absorber in tandem solar cells (TSCs). However, wide-bandgap perovskite solar cells (PVSCs) typically suffer from severe non-radiative recombination loss and therefore exhibit high open-circuit voltage (V _OC) deficits. To address these issues, a 2D octyl-diammonium lead iodide interlayer is adopted onto the hole-transporting layer to induce the formation of an ultrathin quasi-2D perovskite that is close to the hole-selective interface. This approach not only accelerates hole transfer and retards hole accumulation but also reduces the trap density in the perovskite layer on top, thereby efficiently suppresses non-radiative recombination pathways. Consequently, the champion wide-bandgap device (≈1.66 eV) exhibits a power conversion efficiency (PCE) of 21.05% with a V _OC of 1.23 V, where the V _OC deficit of 0.43 V is among the lowest values for inverted wide-bandgap PVSCs. Moreover, by stacking a semi-transparent perovskite top cell on a 1.1 eV Cu₂ZnSn(S,Se)₄ (CZTSSe) bottom cell, a 22.27% PCE was achieved on a perovskite/CZTSSe four-terminal tandem solar cell, paving the way for all-solution-processed, low-cost, and efficient TSCs with mitigated energy loss in the wide-bandgap top cells.

Publication date: 15 February 2022

Source: Chemical Engineering Journal, Volume 430, Part 1

Author(s): Luyao Wang, Xin Wang, Lei Zhu, Shi-Bing Leng, Jianghu Liang, Yiting Zheng, Zhanfei Zhang, Zhiang Zhang, Xiao (Xiao) Liu, Feng Liu, Chun-Chao Chen

Herein, lead acetate and lead thiocyanate are explored as dual lead sources to prepare high-quality methylammonium lead iodide perovskite films in ambient air through an eco-friendly way, which results in unprecedented efficiency for perovskite solar cells prepared from non-halide lead sources. In addition, the device also shows excellent air stability.

Abstract

The realization of highly efficient perovskite solar cells (PSCs) in ambient air is considered to be advantageous for low-cost commercial manufacturing. However, it is fundamentally difficult to achieve comparable device performance to that obtained in an inert atmosphere, especially when the ambient humidity is high. Here, an effective precursor engineering that simultaneously employs non-halide lead acetate and lead thiocyanate lead sources for fabricating high-quality methylammonium lead iodide perovskite films in ambient air with enhanced moisture tolerance, is reported. The presence of Ac^– and SCN^– ions not only enables the facile formation of homogeneous and highly crystalized perovskite films, but also directs the uniform growth of the crystals along the (110) direction. Accordingly, a 20.55% efficiency is demonstrated, one of the best results for air-processed MAPbI₃ PSCs, which is also the highest value achieved with non-halide lead sources. Furthermore, the unencapsulated device shows fivefold prolonged air stability (3600 h) compared to the conventional PbI₂-based PSC. Together with the use of non-toxic antisolvent, this strategy is fully compatible with ambient air operation and thus of great potential for practical applications.

The synergistic strategy of tuning the solution coordination and crystallization process by introducing ionic liquid is implemented to successfully fabricate pinhole-free tin perovskite films with preferential crystal orientation, which possess improved oxidation repellency for Sn(II) and enhanced hydrophobicity. As a result, the stabilization of high-efficiency lead-free tin halide perovskite solar cells is achieved.

Abstract

Tin halide perovskites attract incremental attention to deliver lead-free perovskite solar cells. Nevertheless, disordered crystal growth and low defect formation energy, related to Sn(II) oxidation to Sn(IV), limit the efficiency and stability of solar cells. Engineering the processing from perovskite precursor solution preparation to film crystallization is crucial to tackle these issues and enable the full photovoltaic potential of tin halide perovskites. Herein, the ionic liquid n-butylammonium acetate (BAAc) is used to tune the tin coordination with specific O…Sn chelating bonds and NH…X hydrogen bonds. The coordination between BAAc and tin enables modulation of the crystallization of the perovskite in a thin film. The resulting BAAc-containing perovskite films are more compact and have a preferential crystal orientation. Moreover, a lower amount of Sn(IV) and related chemical defects are found for the BAAc-containing perovskites. Tin halide perovskite solar cells processed with BAAc show a power conversion efficiency of over 10%. This value is retained after storing the devices for over 1000 h in nitrogen. This work paves the way toward a more controlled tin-based perovskite crystallization for stable and efficient lead-free perovskite photovoltaics.

An efficient hybrid quantum dot (QD)/organic film is demonstrated, which involves emerging CsPbI₃ perovskite QDs and Y6 series non-fullerene molecules. Consequently, the CsPbI₃ QD/Y6 hybrid solar cells (HSCs) deliver a champion power conversion efficiency of 15.05%, which is one of the highest reports among QD/organic HSCs.

Abstract

Organic-inorganic hybrid film using conjugated materials and quantum dots (QDs) are of great interest for solution-processed optoelectronic devices, including photovoltaics (PVs). However, it is still challenging to fabricate conductive hybrid films to maximize their PV performance. Herein, for the first time, superior PV performance of hybrid solar cells consisting of CsPbI₃ perovskite QDs and Y6 series non-fullerene molecules is demonstrated and further highlights their importance on hybrid device design. In specific, a hybrid active layer is developed using CsPbI₃ QDs and non-fullerene molecules, enabling a type-II energy alignment for efficient charge transfer and extraction. Additionally, the non-fullerene molecules can well passivate the QDs, reducing surface defects and energetic disorder. The champion CsPbI₃ QD/Y6-F hybrid device has a record-high efficiency of 15.05% for QD/organic hybrid PV devices, paving a new way to construct solution-processable hybrid film for efficient optoelectronic devices.

The MA-free organic-inorganic hybrid perovskite (FAPbI₃) have drawn intense attention. The imidazole bromide functionalized graphene quantum dots is introduced to regulate the interface between SnO₂ layer and FAPbI₃ perovskite layer. The resulting reduced interface defects, better energy level alignment, and better perovskite film achieve a high efficiency of 22.37% with enhanced long-term stability.

Abstract

Organic–inorganic hybrid perovskites have reached an unprecedented high efficiency in photovoltaic applications, which makes the commercialization of perovskite solar cells (PSCs) possible. In the past several years, particular attention has been paid to the stability of PSC devices, which is a critical issue for becoming a practical photovoltaic technology. In particular, the interface-induced degradation of perovskites should be the dominant factor causing poor stability. Here, imidazole bromide functionalized graphene quantum dots (I-GQDs) are demonstrated to regulate the interface between the electron transport layer (ETL) and formamidinium lead iodide (FAPbI₃) perovskite layer. The incorporation of I-GQDs not only reduces the interface defects for achieving a better energy level alignment between ETL and perovskite, but also improves the film quality of FAPbI₃ perovskite including enlarged grain size, lower trap density, and a longer carrier lifetime. Consequently, the planar FAPbI₃ PSCs with I-GQDs regulation achieve a high efficiency of 22.37% with enhanced long-term stability.

Publication date: 18 August 2021

Source: Joule, Volume 5, Issue 8

Author(s): Huachao Zai, Jie Su, Cheng Zhu, Yihua Chen, Yue Ma, Pengxiang Zhang, Sai Ma, Xiao Zhang, Haipeng Xie, Rundong Fan, Zijian Huang, Nengxu Li, Yu Zhang, Yujing Li, Yang Bai, Ziyan Gao, Xueyun Wang, Jiawang Hong, Kangwen Sun, Jingjing Chang

Solar Cells In their Communication on page 16330, Zhijun Ning et al. report the preparation of low-dimensional inorganic tin perovskite solar cells by template growth.

Publication date: 17 February 2021

Source: Joule, Volume 5, Issue 2

Author(s): Jin Hyuck Heo, Fei Zhang, Chuanxiao Xiao, Su Jeong Heo, Jin Kyoung Park, Joseph J. Berry, Kai Zhu, Sang Hyuk Im

Publication date: 20 January 2021

Source: Joule, Volume 5, Issue 1

Author(s): Tianqi Niu, Weiya Zhu, Yiheng Zhang, Qifan Xue, Xuechen Jiao, Zijie Wang, Yue-Min Xie, Ping Li, Runfeng Chen, Fei Huang, Yuan Li, Hin-Lap Yip, Yong Cao