This Perspective reviews the developments of tin-based perovskite solar cells (PSCs) during the period 2014–2019 based on two organic cations (methylammonium vs formamidinium) and two device ...architectures (normal vs inverted) with the strategies of using cocations and coadditives. Unlike their lead-based analogues, tin-based PSCs suffer from the problems of Sn2+/Sn4+ oxidation and film formation. The current best cell is based on an inverted planar FASnI3 device with guanidinium as cocation, SnF2 as additive, and ethylenediammonium iodide as coadditive, which attains record efficiency near 10% with great stability. The device stability and performance might be further improved upon introducing bulky organic cations with a suitable coadditive to form a hybrid 2D/3D crystal structure. Considering the theoretical limit on device efficiency for tin-based PSCs to be ∼33%, there is much room for further performance improvement if the problems can be resolved according to the approaches discussed in this Perspective.
Herein, we report a sequential deposition procedure to passivate the surface of a hybrid mixed cationic tin perovskite (E1G20) with phenylhydrazinium thiocyanate (PHSCN) dissolved in trifluoroethanol ...solvent. The photoluminescence lifetime of the PHSCN film was enhanced by a factor of 6, while the charge-extraction rate from perovskite to C60 layer was enhanced by a factor of 2.5, in comparison to those of the E1G20 film. A slow surface passivation was observed; the performance of the PHSCN device improved upon increasing the storage period to attain an efficiency of 13.5% for a current–voltage scan in the forward bias direction. An inverted effect of hysteresis was observed in that the efficiency of the forward scan was greater than that of the reverse scan. An ion-migration model as a result of the effect of the phenylhydrazinium surface passivation is proposed to account for the observed phenomena. The device was stable upon shelf storage in a glovebox for 3000 h.
The effects of additives SnF2 (10%) and EDAI2 (1%) on the dynamics of carrier relaxation of formamidinium tin triiodide (FASnI3) perovskite were studied using femtosecond transient absorption spectra ...(TAS) with excitation at 600 and 870 nm. The TAS were analyzed according to a parallel sequential kinetic model with a global fit through singular-value decomposition. For excitation at 600 nm, two relaxation paths were found: one involved hot and cold carriers in the bulk state undergoing shallow bulk-defect-mediated charge recombination; the other involved trap carriers in the surface state undergoing deep surface-defect-mediated charge recombination. For excitation at 870 nm, only cold carriers were subjected to the bulk-state relaxation channel. Our spectral results indicate significant effects of the additives on retarding charge recombination in both bulk and surface states as well as decreasing the bandgap renormalization energy, the bandwidth of the photobleaching (PB) band, and the Stokes shift between the PB and photoluminescence bands, explaining how the device performance of FASnI3 solar cells became enhanced in the presence of SnF2 and EDAI2.
Reduced graphene oxides (rGO) are synthesized via reduction of GO with reducing agents as a hole‐extraction layer for high‐performance inverted planar heterojunction perovskite solar cells. The best ...efficiencies of power conversion (PCE) of these rGO cells exceed 16%, much greater than those made of GO and poly(3,4‐ethenedioxythiophene):poly(styrenesulfonate) films. A flexible rGO device shows PCE 13.8% and maintains 70% of its initial performance over 150 bending cycles. It is found that the hole‐extraction period is much smaller for the GO/methylammonium lead‐iodide perovskite (PSK) film than for the other rGO/PSK films, which contradicts their device performances. Photoluminescence and transient photoelectric decays are measured and control experiments are performed to prove that the reduction of the oxygen‐containing groups in GO significantly decreases the ability of hole extraction from PSK to rGO and also retards the charge recombination at the rGO/PSK interface. When the hole injection from PSK to GO occurs rapidly, hole propagation from GO to the indium‐doped tin oxide (ITO) substrate becomes a bottleneck to overcome, which leads to a rapid charge recombination that decreases the performance of the GO device relative to the rGO device.
An anomalous charge‐extraction behavior is observed for the graphene oxide (GO) film showing more rapid hole‐extraction characteristic than that of the reduced graphene oxide (rGO) film, but the corresponding photovoltaic performances show an opposite trend. The rapid charge extraction in GO also leads to a rapid charge recombination so that the GO device shows poorer performance than the rGO device (13.8% vs 16.4%).
We report the effect of the integration of carbon dots (Cdots) in high-performance inverted planar-heterojunction (PHJ) perovskite solar cells (PSCs). We used Cdots to modify the hole-transport layer ...in planar PSC devices. By introducing Cdots on graphene oxide (GO) as hole-transporting layer, the efficiency of the PSC improved significantly from 14.7% in the case of bare GO to 16.2% of the best device with optimized Cdots content. When applying Cdots with an engineered absorption in the UV range as downshifting layer, the device performance was further improved, attaining a maximum PCE of 16.8% (+14%); the stability of the device was also enhanced of more than 20%. Kelvin probe force microscopy (KPFM) and cyclic voltammetry (CV) were employed to analyze the electronic band alignment at the interface between GO/Cdots and the perovskite film. Holes were extracted and transferred to the conductive substrate more efficiently in the presence of Cdots, thus delaying charge recombination. Photoluminescence (PL), transient PL decays and transient photovoltage (TPV) decays investigated the charge-transfer kinetics and proved the retardation of charge recombination. This work reveals an effective enhancement of the performance of planar PSCs by using Cdots/GO as hole transport material.
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•Carbon Dots hybrid material is used in place of PEDOT:PSS as hole transporting material.•UV-Absorbing Carbon Dots is used as downshifting layer to improve the efficiency and the long term stability of the device.•The efficiency improved significantly from 14.7% to 16.8% of the best device with optimized Cdots content.•The presence of Cdots on graphene oxide increases the rate of hole injection and decreases charge recombination.
Overcoming the issue of the stability of tin‐based perovskites is a major challenge for the commercial development of lead‐free perovskite solar cells. To attack this problem, a new organic cation, ...azetidinium (AZ), is incorporated into the crystal structure of formamidinium tin triiodide (FASnI3) to form the mixed‐cation perovskite AZxFA1‐xSnI3. As AZ has a similar size to FA but a larger dipole moment, hybrid AZxFA1‐xSnI3 films exhibit variation in optical and electronic properties on increasing the proportion of AZ. Trifluoromethylbenzene (CF3C6H5) serves as antisolvent to fabricate smooth and uniform perovskite films for the devices with an inverted planar heterojunction structure. The device performance is optimized to produce the greatest efficiency at x=0.15 (AZ15), for which a power conversion efficiency of 9.6 % is obtained when the unencapsulated AZ15 device is stored in air for 100 h. Moreover, the device retains 90 % of its initial efficiency for over 15 days. The significant performance and stability of this device reveal that the concept of mixed cations is a promising approach to stabilize tin‐based perovskite solar cells for future commercialization.
Can we mix it? Yes we can! Mixing 15 % of azetidinium (AZ) inside a FASnI3 perovskite crystal enhances the device performance to attain a power conversion efficiency of 9.6 % with excellent stability for the unencapsulated device, which retains 90 % of its initial performance for over 15 days.
The control of the thickness and porosity of a mesoporous TiO2 layer is important to improve the photovoltaic performance of perovskite solar cells. We produced organized mesoporous TiO2 (om-TiO2) ...layers using a low-cost amphiphilic graft copolymer, poly(vinyl chloride)-graft-poly(oxyethylene methacrylate) (PVC-g-POEM), as a sacrificial template. This simple but effective synthetic approach generates highly mesoporous and well-organized TiO2 nanostructures with interconnected and size-tunable features. Specifically, the average pore size increased with the amount of hydrophobic PVC main chain in the graft copolymer, which acted as the pore forming agent. Perovskite layers were prepared on top of an om-TiO2 layer according to a two-step sequential deposition: after coating the PbI2 solution in dimethylformamide (DMF) on an om-TiO2 substrate, the substrate was prewetted in isopropyl alcohol (IPA) solvent before immersing into a CH3NH3I/IPA solution. This prewetting treatment not only improves the yields of conversion from PbI2 to CH3NH3PbI3, but also increases the size of perovskite crystals with cuboid morphology. On varying the pore size and the film thickness of the om-TiO2 layer, the device performance attained 11.9% of power conversion efficiency (PCE) at pore size 70 nm and film thickness 300 nm. We measured extracted charge densities and decays of transient photovoltage to understand the kinetics of charge recombination in relation to the corresponding device performance.
Next-generation renewable energy sources and perovskite solar cells have revolutionised photovoltaics research and the photovoltaic industry. However, the presence of toxic lead in perovskite solar ...cells hampers their commercialisation. Lead-free tin-based perovskite solar cells are a potential alternative solution to this problem; however, numerous technological issues must be addressed before the efficiency and stability of tin-based perovskite solar cells can match those of lead-based perovskite solar cells. This report summarizes the development of lead-free tin-based perovskite solar cells from their conception to the most recent improvements. Further, the methods by which the issue of the oxidation of tin perovskites has been resolved, thereby enhancing the device performance and stability, are discussed in chronological order. In addition, the potential of lead-free tin-based perovskite solar cells in energy storage systems, that is, when they are integrated with batteries, is examined. Finally, we propose a research direction for tin-based perovskite solar cells in the context of battery applications.
Here, a solvothermal method for synthesis of porous Ni–Co binary oxide (NiCo
2
O
4
) nanorods followed by thermal decomposition is described. The prepared nanorods were characterized by X-ray ...diffraction (XRD), scanning electron microscopy (SEM), and Brunauer Emmett Teller (BET) methods. These porous NiCo
2
O
4
nanostructures were promising candidates in the development of high capacity supercapacitors and having excellent cycling performance due to high specific surface area. In addition, the influence of annealing rate on the structure and electrochemical behavior of the synthesized nanorods was investigated. The results showed that the annealing rate had a direct effect on the crystalline properties and porosity of the nanorods and influenced on their electrochemical behaviors. The nanorods prepared by the annealing rate of about 1 °C min
−1
indicated a rather high capacitance of 600 F g
−1
; moreover, a high retention capacitance of 80 % was achieved even after 1,500 cycles at 5 A g
−1
.
We report here a series of nontoxic and stable bismuth-based perovskite nanocrystals (PeNCs) with applications for photocatalytic reduction of carbon dioxide to methane and carbon monoxide. Three ...bismuth-based PeNCs of general chemical formulas A3Bi2I9, in which cation A+ = Rb+ or Cs+ or CH3NH3 + (MA+), were synthesized with a novel ultrasonication top-down method. PeNC of Cs3Bi2I9 had the best photocatalytic activity for the reduction of CO2 at the gas–solid interface with formation yields 14.9 μmol g–1 of methane and 77.6 μmol g–1 of CO, representing a much more effective catalyst than TiO2 (P25) under the same experimental conditions. The products of the photocatalytic reactions were analyzed using a gas chromatograph coupled with a mass spectrometer. According to electron paramagnetic resonance and diffuse-reflectance infrared spectra, we propose a reaction mechanism for photoreduction of CO2 via Bi-based PeNC photocatalysts to form CO, CH4, and other possible side products.
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