Journal Article Ti3C2TX MXene Hole Transport Layer for Polymer Non-Fullerene Solar Cells Get access Sheenamelia Jones, Sheenamelia Jones Department of Chemistry, Physics and Materials Science, Fayetteville State University, Fayetteville, North Carolina, United States Search for other works by this author on: Oxford Academic Google Scholar Alisha Ware, Alisha Ware Department of Chemistry, Physics and Materials Science, Fayetteville State University, Fayetteville, North Carolina, United States Search for other works by this author on: Oxford Academic Google Scholar Tia Wright, Tia Wright Department of Chemistry, Physics and Materials Science, Fayetteville State University, Fayetteville, North Carolina, United States Search for other works by this author on: Oxford Academic Google Scholar Danielle Keith, Danielle Keith Department of Chemistry, Physics and Materials Science, Fayetteville State University, Fayetteville, North Carolina, United States Search for other works by this author on: Oxford Academic Google Scholar Shubo Han, Shubo Han Department of Chemistry, Physics and Materials Science, Fayetteville State University, Fayetteville, North Carolina, United States Search for other works by this author on: Oxford Academic Google Scholar Daniel Autrey, Daniel Autrey Department of Chemistry, Physics and Materials Science, Fayetteville State University, Fayetteville, North Carolina, United States Search for other works by this author on: Oxford Academic Google Scholar Bhoj Gautam Bhoj Gautam Department of Chemistry, Physics and Materials Science, Fayetteville State University, Fayetteville, North Carolina, United States Corresponding Author: *bgautam@uncfsu.edu Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 28, Issue S1, 1 August 2022, Pages 926–927, https://doi.org/10.1017/S1431927622004068 Published: 01 August 2022

Organometal halides are promising materials for photovoltaic applications, offering tunable electronic levels, excellent charge transport, and simplicity of thin-film device fabrication. Two-dimensional (2D) perovskites have emerged as promising candidates over three-dimensional (3D) ones due to their interesting optical and electrical properties. However, maximizing the power conversion efficiency is a critical issue to improve the performance of these solar cells. In this work, we studied the photophysics of a two-dimensional (2D) perovskite (CH3NH3)2Pb(SCN)2I2 thin film using steady-state and time-resolved absorption and emission spectroscopy and compared it with the three-dimensional (3D) counterpart CH3NH3PbI3. We observed a higher bandgap and faster charge recombination in (CH3NH3)2Pb(SCN)2I2 compared to CH3NH3PbI3. This work provides an improved understanding of fundamental photophysical processes in perovskite structures and provides the guideline for the design, synthesis, and fabrication of solar cells.

Optimization of charge generation and charge transport is crucial for the fabrication of highly efficient polymer solar cells. In the present work, using ultrafast pump-probe spectroscopy and atomic force microscopy, we showed the efficient charge generation and transport at polymer blend MXene interface compared to PEDOT:PSS interface. We observed long charge carrier lifetime, strong photoluminescence of donors and acceptors and higher current on PBDB:ITIC thin film prepared on ITO substrate with MXene. Our study provides the guidelines for the fabrication of inexpensive, flexible, and highly flexible polymer solar cells by interface tuning.

Conjugated polymers have emerged as an interesting class of photovoltaic materials due to their unique properties including light weight, mechanical flexibility and compatibility with roll-to-roll, and non-toxic processing methods. Fullerene derivatives have been extensively used as acceptor materials of choice in organic solar cells (OSC) since the early 1990s but with several drawbacks such as higher production cost, limited absorptivity and spectrum coverage [1], open circuit voltage loss[2], etc. Recently, considerable efforts have been dedicated to the development of non-fullerene acceptors[3]. These acceptors have several advantages over fullerene derivatives, namely high absorption coefficient [4], near infra-red absorption, highly tunable molecular energy levels [4-8], low voltage loss, and complementary donor acceptor absorption[911]. To the date, power conversion efficiency of 16.5%[12] has been reported using these acceptors. There are several factors that influence charge generation and transport in bulk heterojunction OSCs including morphology. In this work, we used perylene diimide (PDI)[13]‐based non fullerene acceptor called SF-PDI (PDI dimer with spirofluorene linker) and donor polymer PBDTBDD-T (poly[(2,6-(4,8-bis(5-(2ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b’]dithiophene))-alt-(5,5-(1’,3’-di-2-thienyl-5’,7’-bis(2ethylhexyl)benzo[1’,2’-c:4’,5’-c’]dithiophene-4,8-dione))]) abbreviated as PBDB-T to prepare the bulk heterojunction. Using Atomic Force Microscopy (AFM) in tapping mode, we studied the impact of thermal annealing on the morphology and phase separation in PBDB-T:SF-PDI blend. The donor polymer PBDB-T and non -fullerene acceptor SF-PDI were purchased from 1-Materials and used as received without further purification. Blend solution of PBDB-T:SF-PDI (1:1 w/w) was prepared by dissolving in chlorobenzene and stirring at 800 C for 12 hours. The concentration of blend solution was 10 mg/ml. The glass substrates were cleaned ultrasonically using deionized water, acetone, and isopropanol for 15 min per cleaning solvent before spin casting. Blend films were prepared by spin casting the solution on glass substrates at 1000 rpm for 60 s. Three thin films were prepared and two of them were annealed at 900 C and 1300 C. The AFM images shown in Figure 1 and 2 indicate that there is a contrast in the morphology of annealed and non-annealed blends. Figure 1 (a, b) shows the atomic force microscopy topography image of PBDB-T:SF-PDI blends at different annealing conditions. The topography images of non-annealed PBDB-T:SF-PDI film reveal the rough surface with root mean square roughness (Rq) in the range of 6.37 nm. Roughness increases upon annealing to 17.7 nm at 900 C and 27.2 nm at 1300 C. AFM phase images (Figure 2 a, b, c) indicate that more distinct phase separated domains are observed in annealed blended thin films compared to non-annealed one. Our results indicate that the annealing improves the nanomorphology of PBDB-T:SF-PDI blend. This difference in morphology and phase separation can result the difference in performance of these solar cells. Corresponding Author: *bgautam@uncfsu.edu Acknowledgments: This work was supported by NSF RIA (HRD 1900998) and EIR (ECCS-1900837).

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Optimization of charge generation in polymer blends is crucial for the fabrication of highly efficient polymer solar cells. While the impacts of the polymer chemical structure, energy alignment, and interface on charge generation have been well studied, not much is known about the impact of polymer aggregation on charge generation. Here, we studied the impact of aggregation on charge generation using transient absorption spectroscopy, neutron scattering, and atomic force microscopy. Our measurements indicate that the 1,8-diiodooctane additive can change the aggregation behavior of poly(benzodithiophene-alt-dithienyl difluorobenzotriazole (PBnDT-FTAZ) and phenyl-C61-butyric acid methyl ester (PCBM)polymer blends and impact the charge generation process. Our observations show that the charge generation can be optimized by tuning the aggregation in polymer blends, which can be beneficial for the design of highly efficient fullerene-based organic photovoltaic devices.