More Like this

1. Low Voltage‐Loss Organic Solar Cells Light the Way for Efficient Semitransparent Photovoltaics

   https://doi.org/10.1002/solr.202200135  

   Luginbuhl, Benjamin R. ; Ko, Seo-Jin ; Ran, Niva A. ; Hu, Huawei ; Becwar, Shona M. ; Karki, Akchheta ; Seifrid, Martin ; Okubo, Takashi ; Wang, Ming ; Ade, Harald W. ; et al ( March 2022 , Solar RRL)

   Organic solar cells that are transparent to visible light are highly desirable for applications such as window treatments or solar greenhouse panels. A key challenge is to simultaneously transmit most photons between 400 and 700 nm while retaining a high short‐circuit current and power conversion efficiency (PCE). Here, organic bulk heterojunction (BHJ) solar cells consisting of a donor polymer (PM2) is reported and the non‐fullerene acceptor ITIC‐Th achieves a PCE of 9.3%, and the BHJ thin films exhibit an average visible transmittance over 40%. This value is achieved primarily due to a very high open‐circuit voltage (V_OC) of 0.93 V, which represents a voltage loss of only 0.50 V relative to the material optical bandgap,E_opt. In PM2:PC₆₁BM devices, this voltage loss increases to 0.62 V (V_OC = 0.82 V). It is found that this difference inV_OCis due to higher nonradiative recombination in the fullerene‐based solar cell, suggesting that non‐fullerene acceptors may lead to better performance in semi‐transparent devices. The optoelectronic properties associated with PM2:ITIC‐Th and PM2:PC₆₁BM blends are further corroborated by different morphological features and local structures at the donor‐acceptor interfaces characterized by atomic force microscopy, X‐ray scattering, and solid‐state NMR spectroscopy techniques.

    

   more » « less
2. High‐Performance Organic Bulk‐Heterojunction Solar Cells Based on Multiple‐Donor or Multiple‐Acceptor Components

   https://doi.org/10.1002/adma.201705706  

   Huang, Wenchao ; Cheng, Pei ; Yang, Yang ; Li, Gang ; Yang, Yang ( January 2018 , Advanced Materials)

   Organic solar cells (OSCs) based on bulk heterojunction structures are promising candidates for next‐generation solar cells. However, the narrow absorption bandwidth of organic semiconductors is a critical issue resulting in insufficient usage of the energy from the solar spectrum, and as a result, it hinders performance. Devices based on multiple‐donor or multiple‐acceptor components with complementary absorption spectra provide a solution to address this issue. OSCs based on multiple‐donor or multiple‐acceptor systems have achieved power conversion efficiencies over 12%. Moreover, the introduction of an additional component can further facilitate charge transfer and reduce charge recombination through cascade energy structure and optimized morphology. This progress report provides an overview of the recent progress in OSCs based on multiple‐donor (polymer/polymer, polymer/dye, and polymer/small molecule) or multiple‐acceptor (fullerene/fullerene, fullerene/nonfullerene, and nonfullerene/nonfullerene) components.

    

   more » « less
3. Ternary System with Controlled Structure: A New Strategy toward Efficient Organic Photovoltaics

   https://doi.org/10.1002/adma.201705243  

   Cheng, Pei ; Wang, Rui ; Zhu, Jingshuai ; Huang, Wenchao ; Chang, Sheng‐Yung ; Meng, Lei ; Sun, Pengyu ; Cheng, Hao‐Wen ; Qin, Meng ; Zhu, Chenhui ; et al ( January 2018 , Advanced Materials)

   Recently, a new type of active layer with a ternary system has been developed to further enhance the performance of binary system organic photovoltaics (OPV). In the ternary OPV, almost all active layers are formed by simple ternary blend in solution, which eventually leads to the disordered bulk heterojunction (BHJ) structure after a spin‐coating process. There are two main restrictions in this disordered BHJ structure to obtain higher performance OPV. One is the isolated second donor or acceptor domains. The other is the invalid metal–semiconductor contact. Herein, the concept and design of donor/acceptor/acceptor ternary OPV with more controlled structure (C‐ternary) is reported. The C‐ternary OPV is fabricated by a sequential solution process, in which the second acceptor and donor/acceptor binary blend are sequentially spin‐coated. After the device optimization, the power conversion efficiencies (PCEs) of all OPV with C‐ternary are enhanced by 14–21% relative to those with the simple ternary blend; the best PCEs are 10.7 and 11.0% for fullerene‐based and fullerene‐free solar cells, respectively. Moreover, the averaged PCE value of 10.4% for fullerene‐free solar cell measured in this study is in great agreement with the certified one of 10.32% obtained from Newport Corporation.

    

   more » « less
4. Donor polymer fluorination doubles the efficiency in non-fullerene organic photovoltaics

   https://doi.org/10.1039/c7ta07882j  

   Bauer, Nicole ; Zhang, Qianqian ; Zhu, Jingshuai ; Peng, Zhengxing ; Yan, Liang ; Zhu, Chenhui ; Ade, Harald ; Zhan, Xiaowei ; You, Wei ( January 2017 , Journal of Materials Chemistry A)

   Donor polymer fluorination has proven to be an effective method to improve the power conversion efficiency of fullerene-based polymer solar cells (PSCs). However, this fluorine effect has not been well-studied in systems containing new, non-fullerene acceptors (NFAs). Here, we investigate the impact of donor polymer fluorination in NFA-based solar cells by fabricating devices with either a fluorinated conjugated polymer (FTAZ) or its non-fluorinated counterpart (HTAZ) as the donor polymer and a small molecule NFA (ITIC) as the acceptor. We found that, similar to fullerene-based devices, fluorination leads to an increased open circuit voltage ( V oc ) from the lowered HOMO level and improved fill factor (FF) from the higher charge carrier mobility. More importantly, donor polymer fluorination in this NFA-based system also led to a large increase in short circuit current ( J sc ), which stems from the improved charge transport and extraction in the fluorinated device. This study demonstrates that fluorination is also advantageous in NFA-based PSCs and may improve performance to a higher extent than in fullerene-based PSCs. In the context of other recent reports on demonstrating higher photovoltaic device efficiencies with fluorinated materials, fluorination appears to be a valuable strategy in the design and synthesis of future donors and acceptors for PSCs. 

   more » « less
5. Noise and detectivity limits in organic shortwave infrared photodiodes with low disorder

   https://doi.org/10.1038/s41528-020-0069-x  

   Wu, Zhenghui ; Li, Ning ; Eedugurala, Naresh ; Azoulay, Jason D. ; Leem, Dong-Seok ; Ng, Tse Nga ( April 2020 , npj Flexible Electronics)

   To achieve high detectivity in infrared detectors, it is critical to reduce the device noise. However, for non-crystalline semiconductors, an essential framework is missing to understand and predict the effects of disorder on the dark current. This report presents experimental and modeling studies on the noise current in exemplar organic bulk heterojunction photodiodes, with 10 donor–acceptor combinations spanning wavelength between 800 and 1600 nm. A significant reduction of the noise and higher detectivity were found in devices using non-fullerene acceptors (NFAs) in comparison to those using fullerene derivatives. The low noise in NFA blends was attributed to a sharp drop off in the distribution of bandtail states, as revealed by variable-temperature density-of-states measurements. Taking disorder into account, we developed a general physical model to explain the dependence of thermal noise on the effective bandgap and bandtail spread. The model provides theoretical targets for the maximum detectivity that can be obtained at different detection wavelengths in inherently disordered infrared photodiodes.

    

   more » « less