Chen Weijie

Solution‐phase van der Waals epitaxy growth of MAPbI₃ perovskite films on MoS₂ flakes is observed. The in‐plane coupling between the perovskite and the MoS₂ crystal lattices leads to perovskite films with larger grain size, lower trap density, and preferential growth orientation. Consequently, the efficiency of fabricated perovskite solar cells is substantially improved by the MoS₂ flakes as interfacial layers.

Abstract

The quality of perovskite films is critical to the performance of perovskite solar cells. However, it is challenging to control the crystallinity and orientation of solution‐processed perovskite films. Here, solution‐phase van der Waals epitaxy growth of MAPbI₃ perovskite films on MoS₂ flakes is reported. Under transmission electron microscopy, in‐plane coupling between the perovskite and the MoS₂ crystal lattices is observed, leading to perovskite films with larger grain size, lower trap density, and preferential growth orientation along (110) normal to the MoS₂ surface. In perovskite solar cells, when perovskite active layers are grown on MoS₂ flakes coated on hole‐transport layers, the power conversion efficiency is substantially enhanced for 15%, relatively, due to the increased crystallinity of the perovskite layer and the improved hole extraction and transfer rate at the interface. This work paves a way for preparing high‐performance perovskite solar cells and other optoelectronic devices by introducing 2D materials as interfacial layers.

The power conversion efficiency of poly(3‐hexylthiophene) P3HT:O‐IDTBR bulk heterojunction solar cells peaks at intermediate (34 kDa) polymer molecular weights (MWs). Combined transient absorption and time‐delayed collection field experiments demonstrate that charges are generated more efficiently at intermediate P3HT MWs compared with high and low MWs.

Large‐scale production of organic solar modules requires low‐cost and reliable materials with reproducible batch‐to‐batch properties. In case of polymers, their (photo)physical properties depend strongly on the polymers’ molecular weight (MW). Herein, the impact of the MW of the donor polymer poly(3‐hexylthiophene) (P3HT) on the photophysics is studied in blends with a recently developed rhodanine‐endcapped indacenodithiophene nonfullerene acceptor (IDTBR), a bulk heterojunction (BHJ) system that potentially fulfills the aforementioned criteria for large‐scale production. It is found that the power conversion efficiency (PCE) increases when the weight‐average MW is increased from 17 kDa (PCE: 4.0%) to 34 kDa (PCE: 6.6%), whereas a further increase in MW leads to a reduced PCE of 4.4%. It is demonstrated that the charge generation efficiency, as estimated from time‐delayed collection field experiments, varies with the P3HT MW and is the reason for the differences in photocurrent and device performance. These findings provide insight into the fundamental photophysical reasons of the MW dependence of the PCE, which is taken into account when using polymer‐based nonfullerene acceptor blends in solar cell devices and modules.

A low temperature–processed metal oxide with excellent mechanical properties and thickness‐insensitivity is exploited as an electron transporting layer for high‐efficiency robust flexible polymer solar cells (PSCs). A record efficiency of 11.5% is achieved for the flexible PSCs, and over 91% of initial efficiency is well maintained after 1500 bending cycles.

Abstract

Landmark power conversion efficiency (PCE) over 14% has been accomplished for single‐junction polymer solar cells (PSCs). However, the inevitable fracture of inorganic transporting layers and deficient interlayer adhesion are critical challenges to achieving the goal of flexible PSCs. Here, a bendable and thickness‐insensitive Al‐doped ZnO (AZO) modified by polydopamine (PDA) has emerged as a promising electron transporting layer (ETL) in PSCs. It has special ductility and adhesion to the active layer for improving the mechanical durability of the device. Nonfullerenes PSCs based on PBDB‐T‐2F:IT‐4F with AZO:1.5% PDA (80 nm) ETL yield the best PCE of 12.7%. More importantly, a prominent PCE, approaching 11.5%, is reached for the fully flexible device based on Ag‐mesh flexible electrode, and the device retains >91% of its initial PCE after bending for 1500 cycles. Such thickness insensitivity, mechanical durability, and interfacial adhesion properties for the inorganic ETLs are desired for the development of flexible and wearable PSCs with reliable photovoltaic performance and large‐area roll‐to‐roll printing manufacture.

Publication date: July 2019

Source: Nano Energy, Volume 61

Author(s): Wei Li, Zuo Xiao, Jinlong Cai, Joel A. Smith, Emma L.K. Spooner, Rachel C. Kilbride, Onkar S. Game, Xianyi Meng, Donghui Li, Huijun Zhang, Mengxue Chen, Robert S. Gurney, Dan Liu, Richard A.L. Jones, David G. Lidzey, Liming Ding, Tao Wang

Graphical abstract

The effects of core structures and film casting conditions on molecular ordering and performance of OSCs based on a series of ladder-type NFAs are studied here. The lamellar crystallization of NFAs was suppressed and converted into H and J-type π-π stacks by blending with the donor and heating induced aggregation.

Publication date: July 2019

Source: Nano Energy, Volume 61

Author(s): Kai Wang, Luyao Zheng, Tao Zhu, Xiang Yao, Chao Yi, Xiaotao Zhang, Yu Cao, Lei Liu, Wenping Hu, Xiong Gong

Graphical abstract

Stable inorganic perovskite CsPbI₃ thin films and solar cells are obtained by low temperature vacuum deposition without the need for high‐temperature annealing steps. Intentional compositional gradients on the samples allow combinatorial evaluation of structure‐property relationships using high‐throughput experimentation techniques, indicating that the perovskite phase is stable for Cs‐rich conditions. Solar cells with efficiency > 12% are demonstrated.

Abstract

The structural phases and optoelectronic properties of coevaporated CsPbI₃ thin films with a wide range of [CsI]/[PbI₂] compositional ratios are investigated using high throughput experimentation and gradient samples. It is found that for CsI‐rich growth conditions, CsPbI₃ can be synthesized directly at low temperature into the distorted perovskite γ‐CsPbI₃ phase without detectable secondary phases. In contrast, PbI₂‐rich growth conditions are found to lead to the non‐perovskite δ‐phase. Photoluminescence spectroscopy and optical‐pump THz‐probe mapping show carrier lifetimes larger than 75 ns and charge carrier (sum) mobilities larger than 60 cm² V⁻¹ s⁻¹ for the γ‐phase, indicating their suitability for high efficiency solar cells. The dependence of the carrier mobilities and luminescence peak energy on the Cs‐content in the films indicates the presence of Schottky defect pairs, which may cause the stabilization of the γ‐phase. Building on these results, p–i–n type solar cells with a maximum efficiency exceeding 12% and high shelf stability of more than 1200 h are demonstrated, which in the future could still be significantly improved, judging on their bulk optoelectronic properties.

Publication date: July 2019

Source: Nano Energy, Volume 61

Author(s): Cong Chen, Zhaoning Song, Chuanxiao Xiao, Dewei Zhao, Niraj Shrestha, Chongwen Li, Guang Yang, Fang Yao, Xiaolu Zheng, Randy J. Ellingson, Chun-Sheng Jiang, Mowafak Al-Jassim, Kai Zhu, Guojia Fang, Yanfa Yan

Graphical abstract

Publication date: July 2019

Source: Nano Energy, Volume 61

Author(s): Waqas Siddique Subhani, Kai Wang, Minyong Du, Shengzhong Frank Liu

Graphical abstract

Publication date: 19 June 2019

Source: Joule, Volume 3, Issue 6

Author(s): Rui Wang, Jingjing Xue, Lei Meng, Jin-Wook Lee, Zipeng Zhao, Pengyu Sun, Le Cai, Tianyi Huang, Zhengxu Wang, Zhao-Kui Wang, Yu Duan, Jonathan Lee Yang, Shaun Tan, Yonghai Yuan, Yu Huang, Yang Yang

Context & Scale

Summary

Graphical Abstract

A polymer solar cell (PSC) with a large active area of 216 cm² and high power conversion efficiency of 7.7% is presented, involving a nonfullerene acceptor and the solution‐processable ZrOx interfacial layer made by blade coating. This represents the highest reported efficiency for PSCs with an active area more than 10 cm². More encouragingly, the large‐area PSC shows good long‐term thermal stability as well.

A polymer solar cell involving a nonfullerene acceptor is made by blade coating. In the ternary bulk‐heterojunction layer, the donor is poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b’]dithiophene))‐co‐(1,3‐di(5‐thiophene‐2‐yl)‐ 5,7‐bis(2‐ethylhexyl)benzo[1,2‐c:4,5‐c’]dithiophene‐4,8‐dione)] (PBDB‐T) and the acceptor is a mixture of 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2’,3’‐d’]‐s‐indaceno[1,2‐b:5,6‐b’]dithiophene) (ITIC) and [6,6]‐phenyl C₇₁‐butyric acid methyl ester (PC₇₁BM). The device structure is an indium tin oxide (ITO)‐coated glass substrate/PEDOT:PSS/ternary active layer/interfacial layer/Al. For a small active area of 0.04 cm², the best power conversion efficiency is 9.8% with the LiF interfacial layer. For a large active area of 216 cm², the best efficiency is 7.7% with the ZrOx interfacial layer. After annealing at 85 °C for 30 days, the large‐area device keeps 75% of the initial efficiency. The efficiency of 4.9% is achieved for a large‐area semi‐transparent device.

The combination of perylene diimide and fullerene results in a new hybrid as electron transporting material (ETM) in inverted perovskite solar cells. This hybrid ETM enables a high power conversion efficiency of 18.6 % and good device stability.

Abstract

Electron transport materials (ETM) play an important role in the improvement of efficiency and stability for inverted perovskite solar cells (PSCs). This work reports an efficient ETM, named PDI‐C₆₀, by the combination of perylene diimide (PDI) and fullerene. Compared to the traditional PCBM, this strategy endows PDI‐C₆₀ with slightly shallower energy level and higher electron mobility. As a result, the device based on PDI‐C₆₀ as electron transport layer (ETL) achieves high power conversion efficiency (PCE) of 18.6 %, which is significantly higher than those of the control devices of PCBM (16.6 %) and PDI (13.8 %). The high PCE of the PDI‐C₆₀‐based device can be attributed to the more matching energy level with the perovskite, more efficient charge extraction, transport, and reduced recombination rate. To the best of our knowledge, the PCE of 18.6 % is the highest value in the PSCs using PDI derivatives as ETLs. Moreover, the device with PDI‐C₆₀ as ETL exhibits better device stability due to the stronger hydrophobic properties of PDI‐C₆₀. The strategy using the PDI/fullerene hybrid provides insights for future molecular design of the efficient ETM for the inverted PSCs.

Publication date: 19 June 2019

Source: Joule, Volume 3, Issue 6

Author(s): Ian Mathews, Sai Nithin Kantareddy, Tonio Buonassisi, Ian Marius Peters

Context & Scale

Summary

By coating n‐butylammonium bromide on wide‐bandgap double‐cation perovskite absorber layers (E _G ≈ 1.72 eV), a thin 2D Ruddlesden–Popper perovskite layer of intermediate phase is formed. The resulting heterostructure mitigates nonradiative recombination and enables a high open‐circuit voltage of up to 1.31 V and stable power output efficiencies of up to 19.4%.

Abstract

In this work, the authors realize stable and highly efficient wide‐bandgap perovskite solar cells that promise high power conversion efficiencies (PCE) and are likely to play a key role in next generation multi‐junction photovoltaics (PV). This work reports on wide‐bandgap (≈1.72 eV) perovskite solar cells exhibiting stable PCEs of up to 19.4% and a remarkably high open‐circuit voltage (V _OC) of 1.31 V. The V _OC‐to‐bandgap ratio is the highest reported for wide‐bandgap organic−inorganic hybrid perovskite solar cells and the V _OC also exceeds 90% of the theoretical maximum, defined by the Shockley–Queisser limit. This advance is based on creating a hybrid 2D/3D perovskite heterostructure. By spin coating n‐butylammonium bromide on the double‐cation perovskite absorber layer, a thin 2D Ruddlesden–Popper perovskite layer of intermediate phases is formed, which mitigates nonradiative recombination in the perovskite absorber layer. As a result, V _OC is enhanced by 80 mV.

Publication date: 19 June 2019

Source: Joule, Volume 3, Issue 6

Author(s): Fei Zhang, Chuanxiao Xiao, Xihan Chen, Bryon W. Larson, Steven P. Harvey, Joseph J. Berry, Kai Zhu

Context & Scale

Summary

Graphical Abstract

In article number 1802094, Jangwon Seo and co‐workers report gravure printing of methylammonium lead iodide for the fabrication of flexible perovskite solar cells. Via the optimization of precursor solutions and processing parameters, the resulting all‐printed device shows 17.2% power conversion efficiency (PCE). The roll‐to‐roll (R2R) process of the gravure printing is also demonstrated, and the partial R2R processed device shows 9.7' PCE.