Chen Weijie

This work provides a simple, effective, and low‐cost method to fabricate a ZnO nanoparticle electron transport layer with a thickness higher than 130 nm. The doping of insulating polymer, polystyrene can not only modify the firm quality of ZnO to improve device performance, but also optimize the reproducibility, mechanical endurance, and ambient stability of the polymer‐based solar cells.

Abstract

The optimization of interfacial layer plays a critical role in the ultimate use of polymer‐based solar cells (PSCs). By introducing an insulating polymer, polystyrene (PS), into the ZnO nanoparticles (NPs) with large particle size, an electron transport layer (ETL) with a thickness of more than 130 nm is produced. The doping of PS not only improves the film quality of ZnO NPs to generate a denser, smoother, and more uniform ETL, but also increases the contact properties between the hydrophilic ZnO and hydrophobic active layer. In comparison to control devices, the power conversion efficiencies (PCEs), short circuit current densities, and fill factors of PSCs with the PS‐modified ETL for a typical fullerene system PTB7‐Th:PC₇₁BM and, also, a nonfullerene system PBDB‐T:ITIC are increased, with PCEs from 8.49% to 9.54% and 10.03% to 11.05%, respectively. The reproducibility, mechanical endurance, and ambient stability of the PSCs with the PS‐modified ZnO NP ETL are significantly improved. The combination of the insulating polymer and ZnO NPs provides a simple, low‐cost way to realize the commercialization of high performance, flexible PSCs.

A Cs₄PbI₆‐mediated method is developed to fabricate cesium (Cs)‐rich perovskite films. It is also found that ≈15% alloying with the organic formamidine (FA) cation can sufficiently stabilize the perovskite phase with excellent phase and UV‐irradiation stability. FA_0.15Cs_0.85PbI₃‐based perovskite solar cells achieve a champion power conversion efficiency of 17.5%.

Abstract

The stability issue is still one of the main limitations of the commercialization of perovskite photovoltaics. The mixed cation FA _x Cs_{1 −x} PbI₃ has shown great promise owing to its improved thermal and moisture stability. However, the study of FA _x Cs_{1 −x} PbI₃ is concentrated on formamidine (FA)‐rich perovskite, whereas cesium (Cs)‐rich FA _x Cs_{1 −x} PbI₃ perovskites are barely studied due to the inevitable phase separation when Cs > 30 mol%. Here, a Cs₄PbI₆‐mediated method is developed to synthesize Cs‐rich FA _x Cs_{1 −x} PbI₃ perovskites. It is demonstrated that Cs₄PbI₆ intermediate phase has a low Cs cation diffusion barrier and therefore offers a fast ion exchange with the preformed FA‐rich perovskite phase to finally form the Cs‐rich FA _x Cs_{1 −x} PbI₃ perovskite. The results indicate that ≈15% alloying with organic FA cations can sufficiently stabilize the perovskite phase with excellent phase and UV‐irradiation stability. The FA_0.15Cs_0.85PbI₃ perovskite solar cells achieve a champion power conversion efficiency of 17.5%, showing the great potential of Cs‐based perovskites for efficient and stable solar cells.

Publication date: October 2020

Source: Nano Energy, Volume 76

Author(s): Yueyue Gao, Zhitao Shen, Furui Tan, Gentian Yue, Rong Liu, Zhijie Wang, Shengchun Qu, Zhanguo Wang, Weifeng Zhang

Publication date: October 2020

Source: Nano Energy, Volume 76

Author(s): Jianming Yang, Qinye Bao, Liang Shen, Liming Ding

Publication date: October 2020

Source: Nano Energy, Volume 76

Author(s): Gaoda Chai, Yuan Chang, Zhengxing Peng, Yanyan Jia, Xinhui Zou, Dian Yu, Han Yu, Yuzhong Chen, Philip C.Y. Chow, Kam Sing Wong, Jianquan Zhang, Harald Ade, Liwei Yang, Chuanlang Zhan

Publication date: October 2020

Source: Nano Energy, Volume 76

Author(s): Jia Zhang, Bin Hu

The terrestrial photovoltaic market is dominated by single‐junction silicon solar cell technology. However, there is a fundamental efficiency limit at 29.4%. This is overcome by multijunction devices. Recently, a GaInP/GaAs//Si wafer‐bonded triple‐junction two‐terminal device is presented with a 33.3% (AM1.5g) efficiency. Herein, it is analyzed how this device is improved to reach a conversion efficiency of 34.1%.

The terrestrial photovoltaic market is dominated by single‐junction silicon solar cell technology. However, there is a fundamental efficiency limit at 29.4%. This is overcome by multijunction devices. Recently, a GaInP/GaAs//Si wafer‐bonded triple‐junction two‐terminal device is presented with a 33.3% (AM1.5g) efficiency. Herein, it is analyzed how this device is improved to reach a conversion efficiency of 34.1%. By improving the current matching, an efficiency of 35% (two terminals, AM1.5g) is expected.

A systematic study of a series of polymer:non‐fullerene acceptor blends is conducted to unify the cumulative effects of voltages losses, charge generation efficiencies, non‐geminate recombination and extraction dynamics, and nuanced morphological differences to the device performance. Deconvolution of the major loss processes in these blends and their connections to the nuanced bulk‐heterojunction morphology and energetics are established.

Abstract

Even though significant breakthroughs with over 18% power conversion efficiencies (PCEs) in polymer:non‐fullerene acceptor (NFA) bulk heterojunction organic solar cells (OSCs) have been achieved, not many studies have focused on acquiring a comprehensive understanding of the underlying mechanisms governing these systems. This is because it can be challenging to delineate device photophysics in polymer:NFA blends comprehensively, and even more complicated to trace the origins of the differences in device photophysics to the subtle differences in energetics and morphology. Here, a systematic study of a series of polymer:NFA blends is conducted to unify and correlate the cumulative effects of i) voltage losses, ii) charge generation efficiencies, iii) non‐geminate recombination and extraction dynamics, and iv) nuanced morphological differences with device performances. Most importantly, a deconvolution of the major loss processes in polymer:NFA blends and their connections to the complex BHJ morphology and energetics are established. An extension to advanced morphological techniques, such as solid‐state NMR (for atomic level insights on the local ordering and donor:acceptor ππ interactions) and resonant soft X‐ray scattering (for donor and acceptor interfacial area and domain spacings), provide detailed insights on how efficient charge generation, transport, and extraction processes can outweigh increased voltage losses to yield high PCEs.

An efficient and stable tin perovskite solar cell with a graded heterostructure which is composed of narrow‐bandgap and wide‐bandgap tin perovskites is reported. Such heterostructure facilitates charge extraction and suppresses the oxidation process of Sn²⁺ to Sn⁴⁺. Consequently, the device achieves a maximum power conversion efficiency of 11% with better operational stability.

Lead‐free tin perovskite solar cells (TPSCs) have attracted widespread attention in recent years due to their low toxicity, suitable bandgap, and high carrier mobility. However, the photovoltage and efficiency of TPSCs are still much lower than those of the lead counterparts because of the high trap density and unfavorable band structure in tin perovskite films. To overcome these issues, efficient and stable TPSCs with a graded heterostructure of light‐absorbing layer are reported, in which the narrow‐bandgap tin perovskite dominates at the bulk, whereas the wide‐bandgap tin perovskite is distributed with a gradient from bulk to surface. This heterostructure can selectively extract the photogenerated charge carriers at the perovskite/electron transport layer interface, reduce the density of trap states, and impede the oxidation process of Sn²⁺ to Sn⁴⁺ in air. As a consequence, this graded heterostructure of tin perovskite layer contributes to an increase of 120 mV in the open‐circuit voltage and a maximum power conversion efficiency of 11% for TPSCs with longer operational stability.

A simple and effective method of fine‐tuning the energy level of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) is demonstrated. The as‐prepared hole‐transporting material aligns well with the highest occupied molecular orbital level of the electron donor in nonfullerene‐based organic photovoltaic (OPV) devices in inverted architecture, reaching a power conversion efficiency of 10%, which would benefit the future commercialization of highly efficient OPV devices.

Solution‐processable hole‐transporting materials are demonstrated to improve the performance of nonfullerene‐based organic photovoltaic devices in an inverted structure. A vanadium oxide (VO _X ) precursor, used as a sol–gel, is mixed with commercial poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to form a well‐dispersed VO _X :PEDOT:PSS solution. The work function and molecular distribution of the VO _X :PEDOT:PSS thin film are examined by ultraviolet photoelectron spectroscopy (UPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS), respectively. Unlike conventional PEDOT:PSS, VO _X :PEDOT:PSS not only is compatible with highly hydrophobic photoactive layers but also aligns well with the highest occupied molecular orbital (HOMO) level of the polymer donor, reaching a power conversion efficiency of 10% (≈100% boost) and achieving an excellent device stability.

Identifying high‐performing organic solar cell blends is still an exhausting process relying on labor and time intensive trial‐and‐error procedures. It is shown that a combination of three simple and abundant techniques, thermal analysis, vapor‐phase‐infiltration imaging, and transient‐absorption spectroscopy, can provide the multiscale materials and processing insights that are sufficient to guide the fast screening of organic solar cell blends.

Abstract

The ever increasing library of materials systems developed for organic solar‐cells, including highly promising non‐fullerene acceptors and new, high‐efficiency donor polymers, demands the development of methodologies that i) allow fast screening of a large number of donor:acceptor combinations prior to device fabrication and ii) permit rapid elucidation of how processing affects the final morphology/microstructure of the device active layers. Efficient, fast screening will ensure that important materials combinations are not missed; it will accelerate the technological development of this alternative solar‐cell platform toward larger‐area production; and it will permit understanding of the structural changes that may occur in the active layer over time. Using the relatively high‐efficiency poly[(5,6‐difluoro‐2,1,3‐benzothiadiazol‐4,7‐diyl)‐alt‐(3,3′′′‐di(2‐octyldodecyl)‐2,2′;5′,2′′;5′′,2′′′‐quaterthiophen‐5,5′′′‐diyl)] (PCE11):phenyl‐C61‐butyric acid‐methyl‐ester acceptor (PCBM) blend systems, it is demonstrated that by means of straight‐forward thermal analysis, vapor‐phase‐infiltration imaging, and transient‐absorption spectroscopy, various blend compositions and processing methodologies can be rapidly screened, information on promising combinations can be obtained, reliability issues with respect to reproducibility of thin‐film formation can be identified, and insights into how processing aids, such as nucleating agents, affect structure formation, can be gained.

Herein, dopant‐free small molecular hole‐transporting materials (SM‐HTMs) for perovskite solar cells with efficiencies of over 15% are reviewed, categorized according to their molecular structures rather than the device configurations and the molecular structures are related with their properties. A future researching direction is also provided on how to design efficient SM‐HTMs.

Abstract

Perovskite solar cells (PSCs) based on conventional hole‐transporting materials (HTMs) have achieved power conversion efficiencies comparable to those of typical inorganic solar cells; however, the dopants used to increase the hole mobility or the film‐forming ability impart these devices with a poor long‐term stability, blocking the industrial commercialization of PSCs. As an alternative, HTMs without any dopants are explored. Herein, dopant‐free small molecular HTMs (SM‐HTMs) are reviewed and the performance based on the analyses of their molecular structures are evaluated. A summary of the designing principle and an outlook of the development of highly efficient SM‐HTMs are presented.

Electronically active ionenes were realized by integration of naphthalene diimide into a polymer backbone. These conductive polymers have a low degree of crystalline order, show a great processing advantage to remove energy barriers between organic semiconductors and metal electrodes, and afford fullerene‐based, non‐fullerene‐based, as well as ternary organic solar cells with high performance and a maximum efficiency of 16.9 %.

Abstract

Self‐doping ionene polymers were efficiently synthesized by reacting functional naphthalene diimide (NDI) with 1,3‐dibromopropane (NDI‐NI) or trans‐1,4‐dibromo‐2‐butene (NDI‐CI) via quaternization polymerization. These NDI‐based ionene polymers are universal interlayers with random molecular orientation, boosting the efficiencies of fullerene‐based, non‐fullerene‐based, and ternary organic solar cells (OSCs) over a wide range of interlayer thicknesses, with a maximum efficiency of 16.9 %. NDI‐NI showed a higher interfacial dipole (Δ), conductivity, and electron mobility than NDI‐CI, affording solar cells with higher efficiencies. These polymers proved to efficiently lower the work function (WF) of air‐stable metals and optimize the contact between metal electrode and organic semiconductor, highlighting their power to overcome energy barriers of electron injection and extraction processes for efficient organic electronics.

Publication date: September 2020

Source: Nano Energy, Volume 75

Author(s): Wu-Qiang Wu, Jun-Xing Zhong, Jin-Feng Liao, Chengxi Zhang, Yecheng Zhou, Wenhuai Feng, Liming Ding, Lianzhou Wang, Dai-Bin Kuang