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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.

    

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2. Tailoring carrier dynamics in perovskite solar cells via precise dimension and architecture control and interfacial positioning of plasmonic nanoparticles

   https://doi.org/10.1039/c9ee03937f  

   Cui, Xun ; Chen, Yihuang ; Zhang, Meng ; Harn, Yeu Wei ; Qi, Jiabin ; Gao, Likun ; Wang, Zhong Lin ; Huang, Jinsong ; Yang, Yingkui ; Lin, Zhiqun ( January 2020 , Energy & Environmental Science)

   Placing plasmonic nanoparticles (NPs) in close proximity to semiconductor nanostructures renders effective tuning of the optoelectronic properties of semiconductors through the localized surface plasmon resonance (LSPR)-induced enhancement of light absorption and/or promotion of carrier transport. Herein, we report on, for the first time, the scrutiny of carrier dynamics of perovskite solar cells (PSCs) via sandwiching monodisperse plasmonic/dielectric core/shell NPs with systematically varied dielectric shell thickness yet fixed plasmonic core diameter within an electron transport layer (ETL). Specifically, a set of Au NPs with precisely controlled dimensions ( i.e. , fixed Au core diameter and tunable SiO 2 shell thickness) and architectures (plain Au NPs and plasmonic/dielectric Au/SiO 2 core/shell NPs) are first crafted by capitalizing on the star-like block copolymer nanoreactor strategy. Subsequently, these monodisperse NPs are sandwiched between the two consecutive TiO 2 ETLs. Intriguingly, there exists a critical dielectric SiO 2 shell thickness, below which hot electrons from the Au core are readily injected to TiO 2 ( i.e. , hot electron transfer (HET)); this promotes local electron mobility in the TiO 2 ETL, leading to improved charge transport and increased short-circuit current density ( J sc ). It is also notable that the HET effect moves up the Fermi level of TiO 2 , resulting in an enhanced built-in potential and open-circuit voltage ( V oc ). Taken together, the PSCs constructed by employing a sandwich-like TiO 2 /Au NPs/TiO 2 ETL exhibit both greatly enhanced J sc and V oc , delivering champion PCEs of 18.81% and 19.42% in planar and mesostructured PSCs, respectively. As such, the judicious positioning of rationally designed monodisperse plasmonic NPs in the ETL affords effective tailoring of carrier dynamics, thereby providing a unique platform for developing high-performance PSCs. 

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3. 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. 

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4. Surface Passivation and Carrier Collection in {110}, {100} and Circular Si Microwire Solar Cells

   https://doi.org/10.1002/aenm.201802154  

   Ro, Yun Goo ; Chen, Renjie ; Liu, Ren ; Li, Nan ; Williamson, Theodore ; Yoo, Jinkyoung ; Sim, Sangwan ; Prasankumar, Rohit P. ; Dayeh, Shadi A. ( October 2018 , Advanced Energy Materials)

   Surface recombination is a major bottleneck for realizing highly efficient micro/nanostructure solar cells. Here, parametric studies of the influence of Si microwire (SiMW) surface‐facet orientation (rectangular with flat‐facets, {110}, {100} and circular), with a fixed height of 10 µm, diameter (D= 1.5–9.5 µm), and sidewall spacing (S= 2.5–8.5 µm), and mesh‐grid density (1–16 mm⁻²) on recombination and carrier collection in SiMW solar cells with radial p‐n junctions are reported. An effective surface passivation layer composed of thin thermally grown silicon dioxide (SiO₂) and silicon nitride (SiN_x) layers is employed. For a fixedDof 1.5 µm, tight SiMW spacing results in improved short‐circuit current density (J_sc= 30.1 mA cm⁻²) and sparse arrays result in open‐circuit voltages (V_oc= 0.552 V) that are similar to those of control Si planar cells. For a fixedS, smallerDresults in better light trapping at shorter wavelengths and higherJ_scwhile largerDexhibits better light trapping at larger wavelengths and a higherV_oc. With a mesh‐grid electrode the power conversion efficiency increases to 15.3%. These results provide insights on the recombination mechanisms in SiMW solar cells and provide general design principles for optimizing their performance.

    

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5. Balanced Charge Transport Optimizes Industry‐Relevant Ternary Polymer Solar Cells

   https://doi.org/10.1002/solr.202000538  

   Szymanski, Robin ; Henry, Reece ; Stuard, Samuel ; Vongsaysy, Uyxing ; Courtel, Stéphanie ; Vellutini, Luc ; Bertrand, Mélanie ; Ade, Harald ; Chambon, Sylvain ; Wantz, Guillaume ( October 2020 , Solar RRL)

   Bulk heterojunction polymer solar cells based on a novel combination of materials are fabricated using industry‐compliant conditions for large area manufacturing. The relatively low‐cost polymer PTQ10 is paired with the nonfullerene acceptor 4TIC‐4F. Devices are processed using a nonhalogenated solvent to comply with industrial usage in absence of any thermal treatment to minimize the energy footprint of the fabrication. No solvent additive is used. Adding the well‐known and low‐cost fullerene derivative PC₆₁BM acceptor to this binary blend to form a ternary blend, the power conversion efficiency (PCE) is improved from 8.4% to 9.9% due to increased fill factor (FF) and open‐circuit voltage (V_OC) while simultaneously improving the stability. The introduction of PC₆₁BM is able to balance the hole–electron mobility in the ternary blends, which is favourable for high FF. This charge transport behavior is correlated with the bulk heterojunction (BHJ) morphology deduced from grazing‐incidence wide‐angle X‐ray scattering (GIWAXS), atomic force microscopy (AFM), and surface energy analysis. In addition, the industrial figure of merit (i‐FOM) of this ternary blend is found to increase drastically upon addition of PC₆₁BM due to an increased performance–stability–cost balance.

    

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