Chen Weijie

Publication date: April 2022

Source: Nano Energy, Volume 94

Author(s): Jiangsheng Yu, Xin Liu, Ziping Zhong, Cenqi Yan, Heng Liu, Patrick W.K. Fong, Qiong Liang, Xinhui Lu, Gang Li

Publication date: April 2022

Source: Nano Energy, Volume 94

Author(s): Zhihao Li, Zhenhan Wang, Chunmei Jia, Zhi Wan, Chongyang Zhi, Can Li, Meihe Zhang, Chao Zhang, Zhen Li

Publication date: April 2022

Source: Nano Energy, Volume 94

Author(s): Daming Zheng, Catherine Schwob, Yoann Prado, Zakarya Ouzit, Laurent Coolen, Thierry Pauporté

Publication date: April 2022

Source: Nano Energy, Volume 94

Author(s): Jiajia Suo, Bowen Yang, Jaeki Jeong, Tiankai Zhang, Selina Olthof, Feng Gao, Michael Grätzel, Gerrit Boschloo, Anders Hagfeldt

A quaternary organic solar cell (OSC) is reported by using two polymer donors (PM6 and L20) along with acceptors Y6 and PC₇₁BM, leading to improvements of opencircuit voltage, fill factor, and power conversion efficiency. The quaternary OSC exhibits a higher charge collection efficiency, expedited charge carrier sweep-out, and reduced charge recombination losses. The suppression on ΔV _oc is attributed to reduced ΔE ₂ (0.143 eV) and ΔE ₃ (0.216 eV).

Multi-component organic solar cells (OSCs) composing of more than two donor and acceptor materials have attracted increasing attention, due to the possibilities to further mitigate voltage loss (ΔV _oc) for the gain of open-circuit voltage (V _oc). However, the control of phase morphology in multi-component blend systems that critically impacts ΔV _oc and the ultimate power conversion efficiency (PCE) is still a challenge. Here, we report a quaternary blend-based strategy for non-fullerene OSCs by using two polymer donors (PM6 and L20) along with acceptors of a non-fullerene (Y6) and PC₇₁BM, leading to concurrent improvements of the V _oc, device fill factor and eventual PCE. The quaternary OSC exhibits the advantages of a higher charge collection efficiency, expedited charge carrier sweep-out, and reduced charge recombination losses. The suppression on ΔV _oc is attributed to the reduced radiative recombination loss below the bandgap (0.143 V) and non-radiative voltage loss (0.216 V). These properties are linked to synergies of modified energetics and film morphology of the quaternary blends. This work demonstrates that incorporating suitable donor and acceptor guest molecules to organic binary blend systems is a highly viable approach for lowering the energy loss in organic bulk heterojunctions towards the boost of photovoltaic performance for realistic energy conversion applications.

Single-walled carbon nanotubes are promising candidates for enhancing charge extraction in organic solar cells due to their exceptional charge transport properties. However, being defect prone and randomly oriented in the active layer crossing multiple donor-acceptor phases, they can also reduce device performance by quenching excitons and trapping charge carriers in a time scale from femtoseconds to microseconds.

Employing single-walled carbon nanotubes (SWNTs) as an additive in the active layer of organic photovoltaics (OPV) to improve charge extraction is gaining weight in the research community. While SWNTs can transport charge carriers orders of magnitudes faster than conventional polymers, they also quench excitons and trap-free charges, reducing device performance. Such influences of SWNTs on OPV device performance remain inadequately explored and incompletely understood. Herein, the impact of SWNTs, enriched in (6,5) chirality, on the charge generation and extraction properties of two different OPV devices is studied by femtosecond-microsecond transient absorption spectroscopy and transient photovoltage/photocurrent techniques. It is shown that depending on the donor material properties (e.g., energetics), SWNTs can reduce carrier generation by quenching the excitons and increase carrier recombination through trapping processes. Then, by performing an analytical calculation of the current–voltage characteristics of the devices using the parameters determined via the transient measurements, it is shown that the increased recombination also relates to morphological changes induced by the SWNTs. These results shed light on the performance limiting factors of the SWNTs when incorporated into the active layer of the solar cells. This work thus can accelerate the blend optimization process for high-performance organic solar cells.

A tight packing in the mixing region effectively enhances the hole transfer and leads to the enlarged and narrow electron density of state. The optimized electronic structure effectively increases carrier density and reduces the recombination losses due to the reduced energy disorder, improving the open-circuit voltage, short-circuit current and fill factor simultaneously.

Abstract

The donor/acceptor interaction in non-fullerene organic photovoltaics leads to the mixing domain that dictates the morphology and electronic structure of the blended thin film. Initiative effort is paid to understand how these domain properties affect the device performances on high-efficiency PM6:Y6 blends. Different fullerenes acceptors are used to manipulate the feature of mixing domain. It is seen that a tight packing in the mixing region is critical, which could effectively enhance the hole transfer and lead to the enlarged and narrow electron density of state (DOS). As a result, short-circuit current (J _SC) and fill factor (FF) are improved. The distribution of DOS and energy levels strongly influences open-circuit voltage (V _OC). The raised filling state of electron Fermi level is seen to be key in determining device V _OC. Energy disorder is found to be a key factor to energy loss, which is highly correlated with the intermolecular distance in the mixing region. A 17.53% efficiency is obtained for optimized ternary devices, which is the highest value for similar systems. The current results indicate that a delicate optimization of the mixing domain property is an effective route to improve the V _OC, J _SC, and FF simultaneously, which provides new guidelines for morphology control toward high-performance organic solar cells.

Publication date: April 2022

Source: Nano Energy, Volume 94

Author(s): Pengyang Wang, Bingbing Chen, Renjie Li, Sanlong Wang, Yucheng Li, Xiaona Du, Ying Zhao, Xiaodan Zhang

The state-of-the-art of all-inorganic perovskite solar cells is reviewed by performing a detailed meta-analysis of key performance parameters. Using a consistent way of determining the bandgap, a unified approach is adopted for analyzing performance losses in perovskite solar cells based on breaking down the losses into several figures of merit representing recombination losses, resistive losses, and optical losses.

Abstract

While halide perovskites have excellent optoelectronic properties, their poor stability is a major obstacle toward commercialization. There is a strong interest to move away from organic A-site cations such as methylammonium and formamidinium toward Cs with the aim of improving thermal stability of the perovskite layers. While the optoelectronic properties and the device performance of Cs-based all-inorganic lead-halide perovskites are very good, they are still trailing behind those of perovskites that use organic cations. Here, the state-of-the-art of all-inorganic perovskites for photovoltaic applications is reviewed by performing detailed meta-analyses of key performance parameters on the cell and material level. Key material properties such as carrier mobilities, external photoluminescence quantum efficiency, and photoluminescence lifetime are discussed and what is known about defect tolerance in all-inorganic is compared relative to hybrid (organic–inorganic) perovskites. Subsequently, a unified approach is adopted for analyzing performance losses in perovskite solar cells based on breaking down the losses into several figures of merit representing recombination losses, resistive losses, and optical losses. Based on this detailed loss analysis, guidelines are eventually developed for future performance improvement of all-inorganic perovskite solar cells.

This study presents an inkjet-printable approach to colorize perovskite photovoltaics to achieve vivid, angle-invariant, and highly customizable colors and color patterns. The colorized solar cells and modules maintain up to 70% of their initial power conversion efficiency (PCE). To demonstrate the viability for building-integrated photovoltaics, a small module in white marble optics exhibiting a PCE of 14% is presented.

The steadily growing market share of building-integrated photovoltaics (BIPVs) places the aesthetics of solar modules in the focus of research and development. In this work, a colorization method based on inkjet-printed reflective pigments is adapted for the emerging perovskite photovoltaics. Herein, not only excellent control of color impression, brightness, and pattern is demonstrated, but also angle invariant color perception, which makes the presented approach stand out among the many published colorization strategies for perovskite solar cells (PSCs). Compared to uncolored reference solar cells, bright magenta and yellow PSCs display a remarkable relative power conversion efficiency (PCE) of up to 65% and more than 11% absolute PCE. Moreover, PSCs with more BIPV-relevant coloring patterns such as a mimic of a marble or corten steel surfaces are demonstrated. The colorization method presented is inexpensive and ready for scalable solar module production. To demonstrate the scalability of the proposed concept, a small-area perovskite solar module (4 cm² aperture area) in white marble optics exhibiting a PCE of almost 14% as a potential application is presented.

Herein, a unique SnO₂ layer to protect the underlaying layers from damage of the sputtered transparent electrode is developed. Moreover, a high-near-infrared transparent perovskite solar cell using cerium-doped indium oxide is prepared, achieving a record power conversion efficiency (PCE) of 17.23%. As a result, a four-terminal perovskite/silicon tandem solar cell with a PCE of 26.14% is obtained.

Two issues need to be resolved when fabricating p–i–n semitransparent perovskite solar cells (ST-PVSCs) for four-terminal (4 T) perovskite/silicon tandem solar cells: 1) damage to the underlying absorber (MAPbI₃), electron transporting layer ([6,6]-phenyl-C₆₁-butyric acid methyl ester, PCBM), and work function (WF) modifier (polyethylenimine, PEI), resulting from the harsh sputtering conditions for the transparent electrodes (TEs) and 2) low average near-infrared transmittance (ANT) of TEs. Herein, a unique SnO₂ layer to protect the MAPbI₃ and PCBM layers is developed and functions as a WF modifier for a new TE (cerium-doped indium oxide, ICO), which exhibits an excellent ANT of 86.7% in the range of 800−1200 nm. Moreover, a MAPbI₃-based p–i–n ST-PVSC is prepared, achieving an excellent power conversion efficiency (PCE) of 17.23%. When it is placed over the Si solar cell, a 4 T tandem solar cell with a PCE of 26.14% is obtained.

A 2D donor–acceptor covalent organic framework nanosheet, [(TPA)₁(TPhT)₁]_CN, is in situ synthesized in a lead iodide layer to regulate the crystallization process of a perovskite film in a sequential deposition method. A covalent organic framework incorporated perovskite solar cell is endowed with a prominent power conversion efficiency of 22.04% and excellent stability.

Abstract

Poor crystallinity of perovskite and extensive defects around grain boundaries are the acknowledged hindrances to obtaining high efficiency and long-term stability for organic metal halide perovskite solar cells (PSCs). Here, a 2D covalent organic framework (2D COF) nanosheets, [(TPA)₁(TPhT)₁]_CN, is first in situ synthesized in a PbI₂ layer with a highly crystalline structure to precisely regulate the crystallization process of perovskite in the sequential deposition method. The existence of 2D COF nanosheets can decelerate intermolecular interdiffusion and induce perovskite crystals to grow along (110) planes with enlarged grain size. Meanwhile, 2D COF nanosheets distributed around the grain boundaries reduce the defect density and promote carriers transporting in the perovskite film. The superior properties of the perovskite film afford the champion PSC device with a power conversion efficiency of 22.04%, which is over 10% higher than the control device. Moreover, the target PSC also demonstrates outstanding long-term stability. It can maintain over 90% of its initial value after 90 days storage in ambient conditions for unencapsulated devices. This work paves a new path for regulating the crystallization process of perovskites via 2D crystalline materials.

Publication date: April 2022

Source: Nano Energy, Volume 94

Author(s): Yang Yang, Minh Tam Hoang, Aman Bhardwaj, Michael Wilhelm, Sanjay Mathur, Hongxia Wang

Placing an ultrathin layer of dopant-free organic triazatruxene molecules as an interfacial layer improves the hole extraction ability and conductivity of the NiO _x through the intermolecular charge transfer effect. The synergetic approach leads to a substantial performance enhancement in dopant-free DTT-EHDI ₂ -based inverted planar perovskite solar cells, achieving 18.15% power conversion efficiency with negligible hysteresis effect.

Interface engineering is an effective approach to decrease nonradiative recombination and the energy barrier at the perovskite/hole transporting layer (HTL) interfaces. To overcome such limitations, an organic semiconductor (DTT-EHDI ₂ ) is proposed, which is, composed of dithienothiophene (DTT) as the core and a planar triazatruxene incorporating an alkyl chain as the side group. This is noted to be an effective interfacial layer for inverted planar perovskite solar cells (PSCs). The altered interface effectively minimizes the detrimental charge recombination and tailors the photoinduced charge transfer dynamics at the interface of the inorganic HTL/perovskite. The π-conjugation in DTT-EHDI ₂ induces high hole mobility and electrical conductivity via electron-donating properties and strong π–π intermolecular interaction. The synergetic approach leads to a substantial performance enhancement in dopant-free DTT-EHDI ₂ -based inverted planar PSCs, achieving 18.15% power conversion efficiency with negligible hysteresis effect. The present approach provides an effective direction of the cost-effective thiophene derivative as an interfacial agent to escalate the optoelectronic performances in photovoltaics.

Herein, 97% bifacial and semitransparent perovskite solar cells give a high equivalent power output of 21.3 W m⁻² under 1 sun illumination using a white back reflector from the rear side. The results show that the side of illumination has a big impact on the light-soak stability of the devices. Cells show promising light stability with illumination from the rear side.

Semitransparent perovskite solar cells (ST-PSCs) are very attractive due to their potential applications in single junctions for building-integrated photovoltaics (BIPV) and in tandem PV technology using low-bandgap bottom solar cells. Despite the high efficiency achieved, the ST-PSCs still suffer low bifaciality, which can limit their overall energy yield for application in BIPV technologies. Furthermore, the knowledge on the long-term light-soaking stability of the ST-PSC from both illumination sides is required to optimize the energy production in the long term. p−i−n ST-PSCs and semitransparent perovskite solar minimodules with comparable and high efficiencies when illuminated from either the rear or the front sides, resulting in the highest reported bifaciality factor of 97%, are demonstrated. A bifacial equivalent power output of 21.3 W m⁻² is achieved for ST-PSCs under 1 sun illumination on the front side, while using a white back reflector from the rear side with 33.5% reflected albedo. However, the side of illumination has a big impact on the light-soak stability of the ST-PSCs. It is observed that the ST-PSC provides more stable output power under illumination from the rear side (n-side) of the stack.

Publication date: March 2022

Source: Nano Energy, Volume 93

Author(s): Xin Yu, Yinhua Lv, Bingyan Xue, Lu Wang, Wanpei Hu, Xinhang Liu, Shangfeng Yang, Wen-Hua Zhang

Publication date: April 2022

Source: Nano Energy, Volume 94

Author(s): Nutifafa Y. Doumon, Lili Yang, Federico Rosei

Publication date: April 2022

Source: Nano Energy, Volume 94

Author(s): Minna Hou, Ya Wang, Xiufang Yang, Meidouxue Han, Huizhi Ren, Yuelong Li, Qian Huang, Yi Ding, Ying Zhao, Xiaodan Zhang, Guofu Hou

Publication date: 19 January 2022

Source: Joule, Volume 6, Issue 1

Author(s): Chao Luo, Guanhaojie Zheng, Feng Gao, Xianjin Wang, Yao Zhao, Xingyu Gao, Qing Zhao

A new mechanism to understand the role of organic ammonium salt (OAS) in improving performances of perovskite solar cells is proposed. Besides passivating defects by itself, OAS also augments the passivation effect of excess PbI₂ on the surface of the perovskite film by dispersing it into a discontinuous layer. Furthermore, using PbI₂ nanosheets fully dispersed in advance boosts the efficiency to 23.14 %.

Abstract

Organic ammonium salts (OASs) have been widely used to passivate perovskite defects. The passivation mechanism is usually attributed to coordination of OASs with unpaired lead or halide ions, yet ignoring their interaction with excess PbI₂ on the perovskite film. Herein, we demonstrate that OASs not only passivate defects by themselves, but also redistribute excess aggregated PbI₂ into a discontinuous layer, augmenting its passivation effect. Moreover, alkyl OAS is more powerful to disperse PbI₂ than a F-containing one, leading to better passivation and device efficiency because F atoms restrict the intercalation of OAS into PbI₂ layers. Inspired by this mechanism, exfoliated PbI₂ nanosheets are adopted to provide better dispersity of PbI₂, further boosting the efficiency to 23.14 %. Our finding offers a distinctive understanding of the role of OASs in reducing perovskite defects, and a route to choosing an OAS passivator by considering substitution effects rather than by trial and error.