Dye-sensitized solar cells (DSCs) convert light into electricity by using photosensitizers adsorbed on the surface of nanocrystalline mesoporous titanium dioxide (TiO
) films along with electrolytes ...or solid charge-transport materials
. They possess many features including transparency, multicolour and low-cost fabrication, and are being deployed in glass facades, skylights and greenhouses
. Recent development of sensitizers
, redox mediators
and device structures
has improved the performance of DSCs, particularly under ambient light conditions
. To further enhance their efficiency, it is pivotal to control the assembly of dye molecules on the surface of TiO
to favour charge generation. Here we report a route of pre-adsorbing a monolayer of a hydroxamic acid derivative on the surface of TiO
to improve the dye molecular packing and photovoltaic performance of two newly designed co-adsorbed sensitizers that harvest light quantitatively across the entire visible domain. The best performing cosensitized solar cells exhibited a power conversion efficiency of 15.2% (which has been independently confirmed) under a standard air mass of 1.5 global simulated sunlight, and showed long-term operational stability (500 h). Devices with a larger active area of 2.8 cm
exhibited a power conversion efficiency of 28.4% to 30.2% over a wide range of ambient light intensities, along with high stability. Our findings pave the way for facile access to high-performance DSCs and offer promising prospects for applications as power supplies and battery replacements for low-power electronic devices
that use ambient light as their energy source.
As a result of their attractive optoelectronic properties, metal halide APbI3 perovskites employing formamidinium (FA+) as the A cation are the focus of research. The superior chemical and thermal ...stability of FA+ cations makes α‐FAPbI3 more suitable for solar‐cell applications than methylammonium lead iodide (MAPbI3). However, its spontaneous conversion into the yellow non‐perovskite phase (δ‐FAPbI3) under ambient conditions poses a serious challenge for practical applications. Herein, we report on the stabilization of the desired α‐FAPbI3 perovskite phase by protecting it with a two‐dimensional (2D) IBA2FAPb2I7 (IBA=iso‐butylammonium overlayer, formed via stepwise annealing. The α‐FAPbI3/IBA2FAPb2I7 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 °C over 500 h.
The desired α‐FAPbI3 perovskite phase is stabilized by protecting it with a two‐dimensional (2D) IBA2FAPb2I7 (IBA=iso‐butylammonium) overlayer, formed via stepwise annealing. The α‐FAPbI3/IBA2FAPb2I7‐based perovskite solar cell (PSC) reached a high power conversion efficiency (PCE) of close to 23 %. It showed excellent operational stability, retaining around 85 % of its initial efficiency under severe combined heat and light stress.
A myriad of studies and strategies have already been devoted to improving the stability of perovskite films; however, the role of the different perovskite crystal facets in stability is still ...unknown. Here, we reveal the underlying mechanisms of facet-dependent degradation of formamidinium lead iodide (FAPbI
) films. We show that the (100) facet is substantially more vulnerable to moisture-induced degradation than the (111) facet. With combined experimental and theoretical studies, the degradation mechanisms are revealed; a strong water adhesion following an elongated lead-iodine (Pb-I) bond distance is observed, which leads to a δ-phase transition on the (100) facet. Through engineering, a higher surface fraction of the (111) facet can be achieved, and the (111)-dominated crystalline FAPbI
films show exceptional stability against moisture. Our findings elucidate unknown facet-dependent degradation mechanisms and kinetics.
We present a facile molecular-level interface engineering strategy to augment the long-term operational and thermal stability of perovskite solar cells (PSCs) by tailoring the interface between the ...perovskite and hole transporting layer (HTL) with a multifunctional ligand 2,5-thiophenedicarboxylic acid. The solar cells exhibited high operational stability (maximum powering point tracking at one sun illumination) with a stabilized
T
S80
(the time over which the device efficiency reduces to 80% after initial burn-in) of 5950 h at 40 °C and a stabilized power conversion efficiency (PCE) over 23%. The origin of high device stability and performance is correlated to the nano/sub-nanoscale molecular level interactions between ligand and perovskite layer, which is further corroborated by comprehensive multiscale characterization. These results provide insights into the modulation of the grain boundaries, local density of states, surface bandgap, and interfacial recombination. Chemical analysis of aged devices showed that molecular passivation suppresses interfacial ion diffusion and inhibits the photoinduced I
2
release that irreversibly degrades the perovskite. The interfacial engineering strategies enabled by multifunctional ligands can expedite the path towards stable PSCs.
The molecular level interface engineering with a multifunctional ligand 2,5-thiophenedicarboxylic acid suppresses interfacial ion diffusion and inhibits I
2
formation, which leads to high operational stability with
T
80
of 3570 h along with PCE of 23.4%.
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%.
Moving a perovskite into the blackThe bandgap of the black α-phase FAPbI3 (where FA is formamidinium) is nearly ideal for solar cells, but it is unstable with respect to the photoinactive yellow ...δ-phase. Lu et al. found that a film of the yellow phase was converted to a highly crystalline black phase by vapor exposure to methylammonium thiocyanate at 100°C, and it retained this structure after 500 hours at 85°C. Solar cells fabricated with this material had a power conversion efficiency of more than 23%. After 500 hours under maximum power tracking and a period of dark recovery, 94% of the original efficiency was retained.Science, this issue p. eabb8985INTRODUCTIONMetal halide perovskite solar cells (PSCs) have reached a power-conversion efficiency (PCE) of 25.2%, thus exceeding other thin-film solar cells. FAPbI3 (where FA is formamidinium) has been shown to be an ideal candidate for efficient, stable PSCs. Obtaining highly crystalline, stable, and pure α-phase FAPbI3 films has been of vital importance. However, FAPbI3 undergoes a phase transition from the black α-phase to the photoinactive δ-phase below 150°C. Previous approaches to overcoming this problem include mixing it with MA, Cs or Br ions. Here, we report a deposition method using methylammonium thiocyanate (MASCN) vapor treatment to convert δ-FAPbI3 to the desired pure α-phase below the thermodynamic phase-transition temperature. Molecular dynamics (MD) simulations show that the SCN– anions promote the formation and stabilization of α-FAPbI3. These vapor-treated FAPbI3 PSCs exhibit outstanding photovoltaic and electroluminescent performance.RATIONALEAlthough the phase transition from δ- to α-phase FAPbI3 requires a high temperature, the treatment of δ-phase FAPbI3 films with MASCN vapor allows the conversion to occur at temperatures below 150°C. MD simulations show that SCN– ions preferentially adsorb on the surface of δ-FAPbI3 to replace iodide ions that are bound to Pb2+. This process disintegrates the top layer of face-sharing octahedra and induces the transition to the corner-sharing architecture of α-FAPbI3. Once the corner-sharing α-form is formed on the top surface, this layer templates the progression of the phase transition from δ- to α-FAPbI3 toward the bulk. Once the pure α-FAPbI3 is formed, its back conversion to the δ-phase is prevented by a high energy barrier.RESULTSWe show a complete conversion from δ- to α-FAPbI3 at 100°C using the MASCN vapor treatment method. This phase transition can also be achieved using FASCN vapor. The vapor-treated FAPbI3 film remained in its pure black phase even after 500 hours of annealing at 85°C, whereas the reference FAPbI3 film formed mainly PbI2 during the heat exposure. X-ray diffraction data showed an improved crystallinity and preferred orientation of the FAPbI3 films after vapor treatment. One- and two-dimensional NMR experiments were used to probe changes in symmetry and quantify the incorporation of MA into the perovskite framework. Time-of-flight secondary ion mass spectrometry measurements confirmed that the MASCN content was mostly located near the surface region of the FAPbI3 films. We used these low-defect-density α-FAPbI3 films to make PSCs with >23% PCE, long-term operational stability, low (330 mV) open-circuit voltage (Voc) loss, and low (0.75 V) turn-on voltage of electroluminescence.CONCLUSIONSCN– anions play a key role in promoting the formation and stabilization of α-FAPbI3. Vapor-treated FAPbI3 films showed long-term thermal stability. MD simulations showed that the pure α-FAPbI3 remained kinetically stable. These findings are important for developing stable and pure black-phase FAPbI3-based PSCs. Our vapor-treated FAPbI3 PSCs showed high efficiency and good long-term stability under maximum power point tracking conditions. Because of its high Voc and high external quantum efficiency electroluminescence yield, pure α-FAPbI3 will be useful for other applications such as light-emitting diodes and photodetectors.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.
Tailoring tin oxide layersMesoporous titanium dioxide is commonly used as the electron transport layer in perovskite solar cells, but electron transport layers based on tin(IV) oxide quantum dots ...could be more efficient, with a better-aligned conduction band and a higher carrier mobility. Kim et al. show that such quantum dots could conformally coat a textured fluorine-doped tin oxide electrode when stabilized with polyacrylic acid. Improved light trapping and reduced nonradiative recombination resulted in a certified power conversion efficiency of 25.4% and high operational stability. In larger-area minimodules, active areas as high as 64 square centimeters maintained certified power conversion efficiencies of more than 20%. —PDS
Passivation of interfacial defects serves as an effective means to realize highly efficient and stable perovskite solar cells (PSCs). However, most molecular modulators currently used to mitigate ...such defects form poorly conductive aggregates at the perovskite interface with the charge collection layer, impeding the extraction of photogenerated charge carriers. Here, a judiciously engineered passivator, 4‐tert‐butyl‐benzylammonium iodide (tBBAI), is introduced, whose bulky tert‐butyl groups prevent the unwanted aggregation by steric repulsion. It is found that simple surface treatment with tBBAI significantly accelerates the charge extraction from the perovskite into the spiro‐OMeTAD hole‐transporter, while retarding the nonradiative charge carrier recombination. This boosts the power conversion efficiency (PCE) of the PSC from ≈20% to 23.5% reducing the hysteresis to barely detectable levels. Importantly, the tBBAI treatment raises the fill factor from 0.75 to the very high value of 0.82, which concurs with a decrease in the ideality factor from 1.72 to 1.34, confirming the suppression of radiation‐less carrier recombination. The tert‐butyl group also provides a hydrophobic umbrella protecting the perovskite film from attack by ambient moisture. As a result, the PSCs show excellent operational stability retaining over 95% of their initial PCE after 500 h full‐sun illumination under maximum‐power‐point tracking under continuous simulated solar irradiation.
A new passivator, 4‐tert‐butylbenzylammonium iodide (tBBAI), is introduced, which accelerates charge extraction while retarding nonradiative recombination, boosting the power conversion efficiency of perovskite solar cells (PSCs) from 20% to 23.5% and reducing the hysteresis to barely detectable levels. tBBAI‐passivated PSCs also show excellent stability, retaining over 95% of their initial PCE after 500 h full‐sun illumination under maximum‐power‐point tracking.
Designing photo-sensitisers with high open-circuit voltage (V oc) is desirable to enhance the power conversion efficiency (PCE) of co-sensitized solar cells. Here, the authors employ a judiciously ...tailored organic sensitiser MS5 with copper electrolyte to achieve a V oc of 1.24 V, and recorded PCE of 34.5% under ambient light.
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