The role of TCNQ for surface and interface passivation in inverted perovskite solar cells

Materials for Renewable and Sustainable Energy https://doi.org/10.1007/s40243-024-00280-9 (2025) 14:11 ORIGINAL PAPER The role of TCNQ for surface and interface passivation in inverted perovskite solar cells Samuel Abicho1,2,3,5 · Bekele Hailegnaw4 · Felix Mayr3 · Munise Cobet3 · Cigdem Yumusak3 · Asefa Sergawi1 · Teketel Yohannes6 · Martin Kaltenbrunner4 · Markus Clark Scharber3 · Getachew Adam Workneh1,2 Received: 11 March 2024 / Accepted: 13 November 2024 © The Author(s) 2024 Abstract The noticeable growth in the power conversion efficiency of solution-processed organo-inorganic halide perovskite solar cells (OIHPSCs) incited the photovoltaic community to look for limitations that hurdle the commercialization process. The surface and interface defects between the perovskite and electron transport layers are among the main challenges that cause significant non-radiative recombination losses, thereby they result in poor performance and stability. In this work, tetracyanoquinodimethane (TCNQ), a strong electron acceptor molecule, is applied at the interface between the photoactive perovskite and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) layers to modify the interface, and enhance device performance and stability. Steady-state and time-resolved photoluminescence measurements were used to characterize the role of the TCNQ passivation in reducing non-radiative recombination of charge carriers. Current density versus voltage (J-V) measurements show improvement in devices open-circuit voltage (Voc), short-circuit current density (Jsc), and fill factor (FF) for devices with TCNQ interface passivation, which is attributed to suppressed non-radiative recombination. In addition, a noticeable improvement in the device’s stability was observed. This study reveals the dual role of TCNQ passivation in improving the photoelectric properties and stability of ambient air processed perovskite devices with the pin architecture. Keywords Organo-inorganic halide perovskite solar cells · Interface passivation · Recombination · Stability · Power conversion efficiency Introduction Getachew Adam Workneh 1 Department of Industrial Chemistry, Addis Ababa Science and Technology University, P.O. Box 16417, Addis Ababa, Ethiopia 2 Sustainable Energy Center of Excellence, Addis Ababa Science and Technology University, P.O. Box 16417, Addis Ababa, Ethiopia 3 Institute of Physical Chemistry, Linz Institute for Organic Solar Cells (LIOS), Johannes Kepler University, Altenberger Str.69, Linz 4040, Austria 4 Division of Soft Matter Physics and LIT Soft Materials Lab, Johannes Kepler University, Altenberger Str.69, Linz 4040, Austria 5 Department of Chemistry, Hawassa University, P.O.Box 05, Hawassa, Ethiopia 6 Department of Chemistry, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia The supply of renewable and green energy is the main hurdle to implementing sustainable development goals. Different renewable energy sources have been widely deployed to mitigate the emission of greenhouse gases. In this regard, the photovoltaic community has been working on different solar cell materials to provide clean, affordable, and sustainable energy to achieve zero greenhouse gas emissions. These days, even though silicon solar cells are relatively efficient, clean, and sustainable, their wide-spread implementation to satisfy the strong demands for renewable energy is limited due to their costly production process of these devices [1, 2]. As an alternative technology, thin film solar cells which provide the advantage of flexibility and comparative affordability have been developed. However, these devices have been criticized for their low power conversion efficiencies (PCE), scarcity of used materials, and toxicity when compared with single-crystal silicon 13 11 Page 2 of 11 solar cells [3]. On the other hand, emerging photovoltaics develop clean and low-cost solar cells using organic and dye materials, even though their PCE and long-term stability are not eye-catching yet. Nowadays, the conspicuous growth of the PCE of organic-inorganic halide perovskite solar cells (OIHP) towards the Shockley-Queisser limit (33%), has astonished the photovoltaic research community [4]. Currently, OIHPSCs achieved a certified record PCE of 26.7%, making it on par with single crystal (non-concentrator) Si solar cells [5]. Their attractive optical and electrical properties like high absorption coefficient [6], large charge carrier diffusion length [7], high charge carrier mobility [8], and tunable bandgap [9] are accounted for such improvement in a short time. These solution-processed polycrystalline devices possess grain boundaries, trap centers, or defects owing to the poor crystallinity, and dangling bonds, thereby different recombination processes take place at their surface or interface [10, 11]. These variables provide room for the interaction of extrinsic and intrinsic factors like moisture, oxygen, light, temperature, and ion migration which can induce defects in either the surface or at the interface of the photo-absorber perovskite layer [12]. Consequently, they limit the generation, extraction, and transportation of the charge carriers and may cause deterioration of the photovoltaic device performance under ambient conditions. Inverted (p-i-n) planar perovskite solar cells known to exhibit better long-term stability compared to their normal (n-i-p) structure, though their PCE lags behind conventional structures. The interface of electron transport layer (ETL) and the photo-absorber perovskite layer is found to be among the major determinants that impact photovoltaic characteristics of such devices [13]. Specifically, the open circuit voltage (Voc) and fill factor (FF) of these devices have been depending on the quality of the interfaces of the charge transporting and OIHP layers. Therefore, interface engineering as the recombination impediment is commonly applied to treat charge trapping centers which cause the recombination of charge carriers [14–18]. Hence, different compounds have been introduced as a thin interlayer in between ETL and photoactive layers, thereby they showed significant improvement in short current density (Jsc), Voc and FF [19–24]. In this work, surface and interface defect mitigation is accomplished using TCNQ as the interface passivator between OIHP and PCBM. The results from measurements of dark current, steady-state photoluminescence, time-resolved photoluminescence, and intensity-modulated photovoltage spectroscopy (IMVS) confirm that our passivation strategy helps to reduces non-radiative recombination. As a result, improvement in Voc, Jsc, and FF of the fabricated OIHPSCs was achieved through interface passivation with TCNQ. This indicates that TCNQ contributes to 13 Materials for Renewable and Sustainable Energy (2025) 14:11 facilitate electron injection from the OIHP layer to PCBM by minimizing defect densities from the interfaces of photoabsorbe (...truncated)