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1. 18.9% Efficient Organic Solar Cells Based on n‐Doped Bulk‐Heterojunction and Halogen‐Substituted Self‐Assembled Monolayers as Hole Extracting Interlayers

   https://doi.org/10.1002/aenm.202202503  

   Lin, Yuanbao ; Zhang, Yadong ; Zhang, Junxiang ; Marcinskas, Mantas ; Malinauskas, Tadas ; Magomedov, Artiom ; Nugraha, Mohamad Insan ; Kaltsas, Dimitris ; Naphade, Dipti R. ; Harrison, George T. ; et al ( October 2022 , Advanced Energy Materials)

   The influence of halogen substitutions (F, Cl, Br, and I) on the energy levels of the self‐assembled hole‐extracting molecule [2‐(9H‐Carbazol‐9‐yl)ethyl]phosphonic acid (2PACz), is investigated. It is found that the formation of self‐assembled monolayers (SAMs) of [2‐(3,6‐Difluoro‐9H‐carbazol‐9‐yl)ethyl]phosphonic acid (F‐2PACz), [2‐(3,6‐Dichloro‐9H‐carbazol‐9‐yl)ethyl]phosphonic acid (Cl‐2PACz), [2‐(3,6‐Dibromo‐9H‐carbazol‐9‐yl)ethyl]phosphonic acid (Br‐2PACz), and [2‐(3,6‐Diiodo‐9H‐carbazol‐9‐yl)ethyl]phosphonic acid (I‐2PACz) directly on indium tin oxide (ITO) increases its work function from 4.73 eV to 5.68, 5.77, 5.82, and 5.73 eV, respectively. Combining these ITO/SAM electrodes with the ternary bulk‐heterojunction (BHJ) system PM6:PM7‐Si:BTP‐eC9 yields organic photovoltaic (OPV) cells with power conversion efficiency (PCE) in the range of 17.7%–18.5%. OPVs featuring Cl‐2PACz SAMs yield the highest PCE of 18.5%, compared to cells with F‐2PACz (17.7%), Br‐2PACz (18.0%), or I‐2PACz (18.2%). Data analysis reveals that the enhanced performance of Cl‐2PACz‐based OPVs relates to the increased hole mobility, decreased interface resistance, reduced carrier recombination, and longer carrier lifetime. Furthermore, OPVs featuring Cl‐2PACz show enhanced stability under continuous illumination compared to ITO/PEDOT:PSS‐based cells. Remarkably, the introduction of the n‐dopant benzyl viologen into the BHJ further boosted the PCE of the ITO/Cl‐2PACz cells to a maximum value of 18.9%, a record‐breaking value for SAM‐based OPVs and on par with the best‐performing OPVs reported to date.

    

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2. New D‐A‐A’‐Configured Small Molecule Donors Employing Conjugation to Red‐shift the Absorption for Photovoltaics

   https://doi.org/10.1002/asia.202000635  

   Wang, Chun‐Kai ; Che, Xiaozhou ; Lo, Yuan‐Chih ; Li, Ya‐Ze ; Wang, Yung‐Hao ; Forrest, Stephen R. ; Liu, Shun‐Wei ; Wong, Ken‐Tsung ( June 2020 , Chemistry – An Asian Journal)

   Four new donor-acceptor-acceptor' (D-A-A')-configured donors, CPNT, DCPNT, CPNBT, and DCPNBT equipped with naphtho[1,2-c:5,6-c']bis([1,2,5]-thiadiazole) (NT) or naphtho[2,3-c][1,2,5]thiadiazole (NBT) as the central acceptor (A) unit bridging triarylamine donor (D) and cyano or dicyanovinylene acceptor (A'), were synthesized and characterized. All molecules exhibit bathochromic absorption shifts as compared to those of the benzothiadiazole (BT)-based analogues owing to improved electron-withdrawing and quinoidal character of NT and NBT cores that lead to stronger intramolecular charge transfer. Favorable energy level alignments with C70 , together with the good thermal stability and the antiparallel dimeric packing render CPNT and DCPNT suitable donors for vacuum-processed organic photovoltaics (OPV)s. OPVs based on DCPNT : C70 active layers displayed the best power conversion efficiency (PCE)=8.3%, along with an open circuit voltage of 0.92 V, a short circuit current of 14.5 mA cm-2 and a fill factor of 62% under 1 sun intensity, simulated AM1.5G illumination. Importantly, continuous light-soaking with AM 1.5G illumination has verified the durability of the devices based on CPNT:C70 and DCPNT : C70 as the active blends. The devices were examined for their feasibility of indoor light harvesting under 500 lux illumination by a TLD-840 fluorescent lamp, giving PCE=12.8% and 12.6%, respectively. These results indicate that the NT-based D-A-A'-type donors CPNT and DCPNT are potential candidates for high-stability vacuum-processed OPVs suitable for indoor energy harvesting. 

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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.

    

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4. 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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5. Enhanced Nucleation of Atomic Layer Deposited Contacts Improves Operational Stability of Perovskite Solar Cells in Air

   https://doi.org/10.1002/aenm.201902353  

   Raiford, James A. ; Boyd, Caleb C. ; Palmstrom, Axel F. ; Wolf, Eli J. ; Fearon, Benjamin A. ; Berry, Joseph J. ; McGehee, Michael D. ; Bent, Stacey F. ( November 2019 , Advanced Energy Materials)

   Metal‐halide perovskites show promise as highly efficient solar cells, light‐emitting diodes, and other optoelectronic devices. Ensuring long‐term stability is now a major priority. In this study, an ultrathin (2 nm) layer of polyethylenimine ethoxylated (PEIE) is used to functionalize the surface of C₆₀for the subsequent deposition of atomic layer deposition (ALD) SnO₂, a commonly used electron contact bilayer for p–i–n devices. The enhanced nucleation results in a more continuous initial ALD SnO₂layer that exhibits superior barrier properties, protecting Cs_0.25FA_0.75Pb(Br_0.20I_0.80)₃films upon direct exposure to high temperatures (200 °C) and water. This surface modification with PEIE translates to more stable solar cells under aggressive testing conditions in air at 60 °C under illumination. This type of “built‐in” barrier layer mitigates degradation pathways not addressed by external encapsulation, such as internal halide or metal diffusion, while maintaining high device efficiency up to 18.5%. This nucleation strategy is also extended to ALD VO_xfilms, demonstrating its potential to be broadly applied to other metal oxide contacts and device architectures.

    

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