Vapor-assisted deposition of highly efficient, stable black-phase FAPbI3 perovskite solar cells

Mixtures of cations or halides with FAPbI3 (where FA is formamidinium) lead to high efficiency in perovskite solar cells (PSCs) but also to blue-shifted absorption and long-term stability issues caused by loss of volatile methylammonium (MA) and phase segregation. We report a deposition method using MA thiocyanate (MASCN) or FASCN vapor treatment to convert yellow δ-FAPbI3 perovskite films to the desired pure α-phase. NMR quantifies MA incorporation into the framework. Molecular dynamics simulations show that SCN- anions promote the formation and stabilization of α-FAPbI3 below the thermodynamic phase-transition temperature. We used these low-defect-density α-FAPbI3 films to make PSCs with >23% power-conversion efficiency and long-term operational and thermal stability, as well as a low (330 millivolts) open-circuit voltage loss and a low (0.75 volt) turn-on voltage of electroluminescence

Realizing high-efficiency perovskite solar cells by passivating triple-cation perovskite films

WOS:000789164100001The photovoltaic performance of perovskite solar cells (PSCs) prepared by the low-temperature solution method has made rapid progress. However, the surface of the film is prone to defects that trap photogenerated charges, resulting in nonradiative recombination energy loss and limiting the open-circuit voltage and overall performance of the device. Interface passivation as an effective method can significantly reduce defects and inhibit nonradiative recombination. Herein, a simple method is introduced to passivate perovskite films by a carboxylated (-COOH) sensitizer that is applied in dye-sensitized solar cells (DSCs), 4-(bis(9,9-dimethyl-9H-flouren-2-yl)amino)-1-naphthoic acid (KTN) molecules. The research results show that the chemical interaction between KTN and iodide vacancies exposing Pb2+ can reduce the nonradiative recombination and elongate the carrier lifetime, which leads to an excellent power conversion efficiency (PCE) with 23% with an obvious increase in open-circuit voltage (V-OC) of 60 mV. Moreover, the defect passivation can significantly enhance the stability of corresponding PSC devices. The unencapsulated device with KTN passivation can readily maintain approximate to 90% of its initial efficiency value after 1400 h. These findings may provide a novel approach for interfacial defect passivation to further promote the performance and stability of PSCs

Stabilization of highly efficient and stable phase-pure FAPbI(3)perovskite solar cells by molecularly tailored 2D-overlayers

WOS:000541488400001 PubMed ID: 32400061As a result of their attractive optoelectronic properties, metal halide APbI(3)perovskites employing formamidinium (FA(+)) as the A cation are the focus of research. The superior chemical and thermal stability of FA(+)cations makes alpha-FAPbI(3)more suitable for solar-cell applications than methylammonium lead iodide (MAPbI(3)). However, its spontaneous conversion into the yellow non-perovskite phase (delta-FAPbI(3)) under ambient conditions poses a serious challenge for practical applications. Herein, we report on the stabilization of the desired alpha-FAPbI(3)perovskite phase by protecting it with a two-dimensional (2D) IBA(2)FAPb(2)I(7)(IBA=iso-butylammonium overlayer, formed via stepwise annealing. The alpha-FAPbI(3)/IBA(2)FAPb(2)I(7)based perovskite solar cell (PSC) reached a high power conversion efficiency (PCE) of close to 23 %. In addition, it showed excellent operational stability, retaining around 85 % of its initial efficiency under severe combined heat and light stress, that is, simultaneous exposure with maximum power tracking to full simulated sunlight at 80 degrees C over 500 h

Correlation between Photoluminescence and Carrier Transport and a Simple In Situ Passivation Method for High-Bandgap Hybrid Perovskites

High-bandgap mixed-halide hybrid perovskites have higher open-circuit voltage deficits and lower carrier diffusion lengths than their lower-bandgap counterparts. We have developed a ligand-assisted crystallization (LAC) technique that introduces additives in situ during the solvent wash and developed a new method to dynamically measure the absolute intensity steady-state photoluminescence and the mean carrier diffusion length simultaneously. The measurements reveal four distinct regimes of material changes and show that photoluminescence brightening often coincides with losses in carrier transport, such as in degradation or phase segregation. Further, the measurements enabled optimization of LAC on the 1.75 eV bandgap FA_0.83Cs_0.17Pb­(I_0.66Br_0.34)₃, resulting in an enhancement of the photoluminescence quantum yield (PLQY) of over an order of magnitude, an increase of 80 meV in the quasi-Fermi level splitting (to 1.29 eV), an increase in diffusion length by a factor of 3.5 (to over 1 μm), and enhanced open-circuit voltage and short-circuit current from photovoltaics fabricated from the LAC-treated films

A molecular photosensitizer achieves a Voc of 1.24 V enabling highly efficient and stable dye-sensitized solar cells with copper(II/I)-based electrolyte

To develop photosensitizers with high open-circuit photovoltage (Voc) is a crucial strategy to enhance the power conversion efficiency (PCE) of co-sensitized solar cells. Here, we show a judiciously tailored organic photosensitizer, coded MS5, featuring the bulky donorN-(2’,4’-bis(dodecyloxy)-[1,1’-biphenyl]-4-yl)-2’,4’-bis(dodecyloxy)-N-phenyl-[1,1’-biphenyl]-4-amineand the electron acceptor 4-(benzo[c][1,2,5]thiadiazol-4-yl)benzoic acid. Employing MS5 with a copper (II/I) electrolyte enables a dye-sensitized solar cell (DSC) to achieve a strikingly high Voc of 1.24 V, with the Voc deficit as low as 130 mV and an ideality factor of merely 1.08. The co-sensitization of MS5 with the wider spectral-response dye XY1b produces a highly efficient and stable DSC with the PCE of 13.5% under standard AM1.5 G, 100 mW cm−2 solar radiation. Remarkably, the co-sensitized solar cell (active area of 2.8 cm2) presents a record PCE of 34.5% under ambient light, rendering it very attractive as an ambient light harvesting energy source for low power electronics

Low-Cost Dopant Additive-Free Hole-Transporting Material for a Robust Perovskite Solar Cell with Efficiency Exceeding 21%

Developing hole-transporting materials (HTMs) with appropriate molecular configuration and charge mobility is important to improve perovskite solar cell (PSC) photovoltaic performance and their feasibility for commercialization. In this work, a novel pyramidal-shaped low-cost HTM coded MeOTTVT is prepared through extension of pi-conjugation based on a triphenylamine core. Carbon-carbon double bonds are introduced between the core and p-methoxyl triphenylamine to improve the planarity of the HTM, favoring intermolecular stacking of MeOTTVT and thus improving the hole mobility of the corresponding hole-transporting layer (HTL). The p-methoxyl triphenylamine-endowed HTM benefits from a highest occupied molecular orbital level well-aligned with the perovskite active layer, facilitating effective hole extraction. The champion PSC using an MeOTTVT-based dopant additive-free HTL yielded a power conversion efficiency (PCE) up to 21.30%, which is considered one of the best-performing PSCs employing a dopant additive-free small molecule HTM. In addition, the MeOTTVT-based dopant additive-free HTL exhibits outstanding thermal stability and high glass-transition temperature (T-g = 137.1 degrees C), combined with a more hydrophobic surface; PSCs based on an MeOTTVT dopant additive-free HTL exhibit outstanding stability against moisture, 1 sun illumination, and thermal stress

Synergistic Effect of Fluorinated Passivator and Hole Transport Dopant Enables Stable Perovskite Solar Cells with an Efficiency Near 24%

Long-term durability is critically important for the commercialization of perovskite solar cells (PSCs). The ionic character of the perovskite and the hydrophilicity of commonly used additives for the hole-transporting layer (HTL), such as lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) and tert-butylpyridine (tBP), render PSCs prone to moisture attack, compromising their long-term stability. Here we introduce a trifluoromethylation strategy to overcome this drawback and to boost the PSC's solar to electric power conversion efficiency (PCE). We employ 4-(trifluoromethyl)benzylammonium iodide (TFMBAI) as an amphiphilic modifier for interfacial defect mitigation and 4-(trifluoromethyl)pyridine (TFP) as an additive to enhance the HTL's hydrophobicity. Surface treatment of the triple-cation perovskite with TFMBAI largely suppressed the nonradiative charge carrier recombination, boosting the PCE from 20.9% to 23.9% and suppressing hysteresis, while adding TFP to the HTL enhanced the PCS's resistance to moisture while maintaining its high PCE. Taking advantage of the synergistic effects resulting from the combination of both fluoromethylated modifiers, we realize TFMBAI/TFP-based highly efficient PSCs with excellent operational stability and resistance to moisture, retaining over 96% of their initial efficiency after 500 h maximum power point tracking (MPPT) under simulated 1 sun irradiation and 97% of their initial efficiency after 1100 h of exposure under ambient conditions to a relative humidity of 60-70%

Cyclopentadiene-Based Hole-Transport Material for Cost-Reduced Stabilized Perovskite Solar Cells with Power Conversion Efficiencies Over 23%

Hole transport materials (HTM) are an important component in perovskite solar cells (PSC). Despite a multitude of HTMs developed in recent years, only few of them lead to solar cells with efficiencies over 20%. Therefore, it is still a challenge to develop high-performing HTMs, which have ideal energy levels of the frontier orbitals, are highly efficient in transporting charges, and stabilize the solar cell at the same time. In this work, the development of a structurally novel molecular HTM, CPDA 1, is described which is based on a common cyclopentadiene core and can be efficiently and inexpensively synthesized from readily available starting materials, which is important for future realization of low-cost photovoltaics on larger scale. Due to excellent optoelectronic, thermal, and transport properties, CPDA 1 not only meets the envisioned properties by reaching high efficiencies of 23.1%, which is among the highest reported to date, but also contributes to a respectable long-term stability of the PSCs