2023, Fakharuddin, Azhar, Armadorou, Konstantina‐Kalliopi, Zorba, Leandros P., Tountas, Marinos, Seewald, Tobias, Schütz, Emilia R., Schmidt-Mende, Lukas, Vougioukalakis, Georgios C., Nazeeruddin, Mohammad Khaja, Vasilopoulou, Maria

Inverted perovskite solar cells (PSCs) have attracted increasing attention in recent years owing to their low-temperature fabrication proces s. However, they suffer from a limited number of electron transport materials available with [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) to be the most widely studied based on its appropriate energy levels and high electron mobility. The low relative permittivity and aggregation tendency upon illumination of PCBM, however, compromises the solar cell efficiency whereas its modest hydrophobicity negatively impacts on the device stability. Alternative electron transport materials with desired properties and appropriate degree of hydrophobicity are thus desirable for further developments in inverted PSCs. Herein, we synthesize a triethyleneglycol C₆₀ mono-adduct derivative (termed as EPF03) and test it as a novel electron transport material to replace PCBM in inverted PSCs based on a quadruple cation (RbCsMAFA) perovskite. We also compare this derivative with two novel fullerenes decorated with two (EPF01) or one dodecyl (EPF02) long side chains. The latter two fail to perform efficiently in inverted PSCs whereas the former enabled a power conversion efficiency of 18.43%, which represents a 9% improvement compared to the reference device using PCBM (17.21%). The enhanced performance mainly stems from improved electron extraction and reduced recombination enabled by the insertion of the large relative permittivity amongst other properties of EPF03. Furthermore, our results indicate that triethylene glycol side chains can also passivate perovskite trap states, suppress ion migration and enhance photostability and long-term stability of EPF03 based perovskite solar cells.

2023, Qureshi, Akbar Ali, Javed, Sofia, Akram, Muhammad Aftab, Schmidt-Mende, Lukas, Fakharuddin, Azhar

Inorganic–organic metal halide perovskite solar cells (PSCs) show power conversion efficiency values approaching those of state-of-the-art silicon solar cells. In a quest to find suitable charge transport materials in PSCs, hematite (α-Fe₂O₃) has emerged as a potential electron transport layer (ETL) in n–i–p planar PSCs due to its low cost, UV light stability, and nontoxicity. Yet, the performance of α-Fe₂O₃-based PSCs is far lower than that of state-of-the-art PSCs owing to the poor quality of the α-Fe₂O₃ ETL. In this work, solvent-assisted crystallization of α-Fe₂O₃ ETLs was carried out to examine the impact of solvents on the optoelectronic properties of α-Fe₂O₃ thin films. Among the various solvents used in this study (deionized water, ethanol, iso-propanol, and iso-butanol), optimized ethanol-based α-Fe₂O₃ ETLs lead to champion device performance with a power conversion efficiency of 13% with a reduced hysteresis index of 0.04 in an n–i–p-configured PSC. The PSC also exhibited superior long-term inert and ambient stabilities compared to a reference device made using a SnO₂ ETL. Through a series of experiments spanning structural, morphological, and optoelectronic properties of the various α-Fe₂O₃ thin films and their devices, we provide insights into the reasons for the improved photovoltaic performance. It is noted that the formation of a pinhole-free compact morphology of ETLs facilitates crack-free surface coverage of the perovskite film atop an α-Fe₂O₃ ETL, reduces interfacial recombination, and enhances charge transfer efficiency. This work opens up the route toward novel ETLs for the development of efficient and photo-stable PSCs.

2022, Polydorou, Ermioni, Verouti, Maria, Soultati, Anastasia, Armadorou, Konstantina-Kalliopi, Verykios, Apostolis, Filippatos, Petros-Panagis, Galanis, George, Palilis, Leonidas C., Fakharuddin, Azhar, Vasilopoulou, Maria

Earth-abundant transition metal oxides deposited at room temperature with low-cost methods suitable for large area manufacturing can offer advances in many fields of energy related devices. Here we report the room-temperature deposition of a fluorine-doped tantalum pentoxide using a home-made, low-cost hot-wire deposition system. This novel tantalum oxyfluoride material is super hydrophobic, ultra-transparent within the visible spectrum, and possesses adequate conductivity and suitable valence band and conduction band extrema for acting as efficient hole extraction and electron blocking layer in organic solar cells with the forward architecture. By inserting this material in the form of nanoparticles deposited on top of the commonly used as hole transport layer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, higher efficiencies compared to the reference cells without the nanoparticles were demonstrated in solar cells based on blends of polymer donors with either a fullerene (where maximum achieved efficiency was improved from 6.07% to 7.90%) or a non-fullerene acceptor (reaching values of 13.48% compared to 11.32% of the reference cell). Moreover, significant improvement in device stability was achievd in unencapsulated devices continuously exposed in a humid environment for 500 h. This work demonstrates the unambiguous potential of well-designed metal oxide materials as charge transport and blocking interlayers and protective buffers in organic solar cells and beyond.

2022, Fakharuddin, Azhar, Gangishetty, Mahesh K., Abdi-Jalebi, Mojtaba, Chin, Sang-Hyun, Bin Mohd Yusoff, Abd Rashid, Congreve, Daniel N., Tress, Wolfgang, Deschler, Felix, Vasilopoulou, Maria, Bolink, Henk J.

Light-emitting diodes based on halide perovskites have undergone rapid development in recent years and can now offer external quantum efficiencies of over 23%. However, the practical application of such devices is still limited by a number of factors, including the poor efficiency of blue-emitting devices, difficulty in accessing emission wavelengths above 800 nm, a decrease in external quantum efficiency at high current density, a lack of understanding of the effect of the electric field on mobile ions present in the perovskite materials, and short device lifetimes. Here we review the development of perovskite light-emitting diodes. We examine the key challenges involved in creating efficient and stable devices, and consider methods to alleviate the poor efficiency of blue-emitting devices, leverage emission in the long infrared region and create spin-polarized light-emitting diodes.

2023, Haider, Muhammad Irfan, Hu, Hao, Seewald, Tobias, Ahmed, Safeer, Sultan, Muhammad, Schmidt-Mende, Lukas, Fakharuddin, Azhar

Defects present at the surface or within the bulk of halide perovskites act as a barrier to charge transfer/transport, induce nonradiative recombination thereby limit open-circuit voltage (VOC), and accelerate degradation in the perovskite solar cells (PSCs). Passivation of these defects at surfaces, interfaces, and grain boundaries to suppress the charge recombination is therefore imperative to improving photovoltaic performance in the PSCs. Herein, a facile posttreatment of perovskite surface by ethylenediamine (EDA) via mixed solvent vapor annealing method is reported. The results show that only a trace amount of EDA causes significant suppression of nonradiative recombination leading to over 100 mV increased VOC and ≈22% improvement in power conversion efficiency (PCE) of the inverted PSCs. The key reasons for this improvement are an upward shift in the Fermi energy level, reduced lattice strain and Urbach energy, and reduction in nonradiative recombination upon EDA passivation. These lead to a PCE exceeding 20% up from 16% for a nonpassivated film. The unencapsulated EDA-modified PSCs also demonstrate an improved shelf-life and retain 87% of the initial PCE after 850 h.

2022-11-02, Ali, Israt, Faraz Ud Din, Muhammad, Cuzzupe, Daniele T., Fakharuddin, Azhar, Louis, Hitler, Nabi, Ghulam, Gu, Zhi-Gang

PEDOT:PSS is a commonly used hole-transport layer (HTL) in inverted perovskite solar cells (PSCs) due to its compatibility with low-temperature solution processing. However, it possesses lower conductivity than other conductive polymers and metal oxides, along with surface defects, limiting its photovoltaic performance. In this study, we introduced two-dimensional Ti₃C₂T_x (MXene) as an additive in the PEDOT:PSS HTL with varying doping concentrations (i.e., 0, 0.03, 0.05, and 0.1 wt.%) to tune the electrical conductivity of PEDOT:PSS and to modify the properties of the perovskite film atop it. We noted that the grain size of the CH₃NH₃PbI₃ (MAPI₃) perovskite layer grown over an optimal concentration of MXene (0.03 wt.%)-doped PEDOT:PSS increased from 250 nm to 400 nm, reducing charge recombination due to fewer grain boundaries. Ultraviolet photoelectron spectroscopy (UPS) revealed increased work function (WF) from 4.43 eV to 4.99 eV with 0.03 wt.% MXene doping, making the extraction of holes easier due to a more favorable energy level alignment with the perovskite. Quantum chemical investigations based on density functional theory (DFT) were conducted at the ωB97XD/6-311++G(d,p) level of theory to provide more insight into the stability, bonding nature, and optoelectronic properties of the PEDOT:PSS–MXene system. The theoretical investigations revealed that the doping of PEDOT:PSS with Ti₃C₂T_x could cause a significant effect on the electronic properties of the HTL, as experimentally demonstrated by an increase in the electrical conductivity. Finally, the inverted PSCs employing 0.03 wt.% MXene-doped PEDOT:PSS showed an average power conversion efficiency (PCE) of 15.1%, up from 12.5% for a reference PSC employing a pristine PEDOT:PSS HTL. The champion device with a 0.03 wt.% MXene–PEDOT:PSS HTL achieved 15.5% PCE.

2022, Soultati, Anastasia, Tountas, Marinos, Fakharuddin, Azhar, Skoulikidou, Maria-Christina, Verykios, Apostolis, Armadorou, Konstantina-Kalliopi, Tzoganakis, Nikolaos, Vidali, Veroniki P., Coutsolelos, Athanassios G., Vasilopoulou, Maria

The presence of defects formed during the growth and crystallization of perovskite films is a limiting factor to achieve high efficiency and stability in perovskite solar cells. Here, we present a robust route to passivate bulk and surface defects in perovskite films by using an amino-functionalized BODIPY fluorophore. The addition of amino-BODIPY into the prototype methyl ammonium lead iodide (MAPbI3) perovskite solution significantly altered the nanomorphology of the perovskite film and alleviated the defect formation leading to efficiency enhancement and prolonged stability of perovskite solar cells with a regular structure. Similar results were obtained when using the BODIPY fluorophore in chlorobenzene (CB)-based antisolvent treatment of spin-coated perovskite films in inverted perovskite solar cells. In addition, reduction in the electron extraction barrier was evidenced. Our approach represents a universal passivation methodology for boosting the efficiency and stability in both regular and inverted perovskite solar cells.

2023, Ganesh, Gayathry, Yasin, Amina, Misnon, Izan Izwan, Fakharuddin, Azhar, Schmidt-Mende, Lukas, Ab Rahim, Mohd Hasbi, Thomas, Sabu, Jose, Rajan

Perovskite solar cells (PSCs) are intensively studied over the past decade to enhance the renewable contribution to the total energy mix; however, their market potential is hampered mostly by their poor operational stability. Polymers as encapsulants, UV-filters, charge transport layers, and interfacial layers are shown to be a potential remedy not only to improve stability but also to positively contribute to other figures of merits of solar cells. Highly efficient PSCs (>15 %) with prolonged operational stability (>3000 h) in various device architectures including fibres, yarns, and woven and knitted cloths are reported using perovskite embedded polymers. This article critically and comprehensively reviews the synergistic interactions between various polymers and the organic–inorganic lead halide perovskite material to establish a structure–property correlation and to examine the viability of the PSCs technology for practical deployment. Mechanistic details of polymers in the photoactive, charge transport and interfacial layers on the morphology, optical and photovoltaic properties, and stability are analysed and discussed. Particularly on stability, the role of polymers on defect tolerance, phase and structure evolution, and external stimuli (heat, moisture, light, electric field, and oxygen) are elaborated. The dielectric properties of polymers enable them to be superior encapsulants over their corresponding monomers or other organic molecules. Based on these broad considerations, adopting the polymeric approach is shown to be a more efficient and greener leap towards the sustainable commercialization of perovskites.

2022-09-21, Vasilopoulou, Maria, Kim, Hyeong Pil, Kim, Byung Soon, Reo, Youjin, Ximim Gavim, Anderson Emanuel, Conforto, Julio, Fakharuddin, Azhar, Nazeeruddin, Mohammad Khaja, Noh, Yong-Young, Rashid Bin Mohd Yusoff, Abd

Here, we report photonic nanostructures replicated from the adaxial epidermis of flower petals onto light-polymerized coatings using low-cost nanoimprint lithography at ambient temperature. These multifunctional nanocoatings are applied to confer enhanced light trapping, water repellence, and UV light and environmental moisture protection features in perovskite solar cells. The former feature helps attain a maximum power conversion efficiency of 24.61% (21.01% for the reference cell) without any additional device optimization. Added to these merits, the nanocoatings also enable stable operation under AM 1.5G and UV light continuous illumination or in real-world conditions. Our engineering approach provides a simple way to produce multifunctional nanocoatings optimized by nature's wisdom.

2022, Schütz, Emilia R., Fakharuddin, Azhar, Yalcinkaya, Yenal, Ochoa-Martinez, Efrain, Bijani, Shanti, Mohd Yusoff, Abd. Rashid bin, Vasilopoulou, Maria, Seewald, Tobias, Steiner, Ullrich, Schmidt-Mende, Lukas

Considerable efforts have been devoted to optimizing and controlling the morphology and electronic properties of lead halide perovskites. The defect density of a perovskite layer strongly depends on the processing conditions. Consequently, the fabrication process of high-quality films is often complex, and reproducibility is a challenge. In this work, we present a methylamine gas-based method to recrystallize perovskite layers of any given quality in a controlled way, leading to millimeter-sized domains. Crystallinity significantly increases upon methylamine treatment, and crystal growth follows a preferred orientation. Photoluminescence- and space-charge limited current measurements show that the trap density halves after recrystallization. Conductive atomic force microscopy measurements show a higher surface conductivity and an improved spatial homogeneity after methylamine treatment. When applied in photodetectors, the improved film quality of the recrystallized films leads to increased detectivities of ≈4 × 10¹¹ Jones compared to 3 × 10⁹ Jones of a reference device. The response time falls from 0.1 to 10⁻⁵ s upon methylamine treatment. Our work, thus, presents a promising route to fabricating reproducible, high-quality perovskite films through well-controllable recrystallization.