The stability of a tin‐based perovskite solar cell is a major challenge. Here, hybrid tin‐based perovskite solar cells in a new series that incorporate a nonpolar organic cation, guanidinium (GA+), ...in varied proportions into the formamidinium (FA+) tin triiodide perovskite (FASnI3) crystal structure in the presence of 1% ethylenediammonium diiodide (EDAI2) as an additive, are reported. The device performance is optimized at a precursor ratio (GAI:FAI) of 20:80 to attain a power conversion efficiency (PCE) of 8.5% when prepared freshly; the efficiencies continuously increase to attain a record PCE of 9.6% after storage in a glove‐box environment for 2000 h. The hybrid perovskite works stably under continuous 1 sun illumination for 1 h and storage in air for 6 days without encapsulation. Such a tin‐based perovskite passes all harsh standard tests, and the efficiency of a fresh device, 8.3%, is certified. The great performance and stability of the device reported herein attains a new milestone for lead‐free perovskite solar cells on a path toward commercial development.
Hybrid cation (guanidinium/formamidinium) tin‐based perovskites that give a new performance record for lead‐free perovskite solar cells (power conversion efficiency = 9.6%) are demonstrated. The fabricated devices show an incredible light‐soaking stability for continuous 1 sun illumination for 1 h, and the device passes all harsh verification steps to attain a certified efficiency of 8.3% for a fresh cell.
To dye for: A porphyrin chromophore, which is integrated into a donor–acceptor dye as a π‐conjugated bridge (see picture), exhibits an unprecedented efficiency of 11 % when used as a photosensitizer ...in a double‐layer TiO2 film. A greatly enhanced photovoltaic performance is observed when the porphyrin dye is cosensitized with a metal‐free dye that has a complementary spectral response.
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.
The iodide/triiodide redox shuttle has limited the efficiencies accessible in dye-sensitized solar cells. Here, we report mesoscopic solar cells that incorporate a Co (II/III) tris(bipyridyl)—based ...redox electrolyte in conjunction with a custom synthesized donor-π-bridge-acceptor zinc porphyrin dye as sensitizer (designated YD2-o-C8). The specific molecular design of YD2-o-C8 greatly retards the rate of interfacial back electron transfer from the conduction band of the nanocrystalline titanium dioxide film to the oxidized cobalt mediator, which enables attainment of strikingly high photovoltages approaching 1 volt. Because the YD2-o-C8 porphyrin harvests sunlight across the visible spectrum, large photocurrents are generated. Cosensitization of YD2-o-C8 with another organic dye further enhances the performance of the device, leading to a measured power conversion efficiency of 12.3% under simulated air mass 1.5 global sunlight.
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%).
Four X‐shaped quinoxaline‐based organic dyes, PQx (1), TQx, (2), PQxD (3), and TQxD (4) (D = dye sensitizers) are developed and served as p‐type self‐assemble monolayer (SAM) for tin perovskite solar ...cells (TPSC). Thermal, optical, and electrochemical properties of these SAMs are thoroughly investigated and characterized. Tin perovskite layers are successfully deposited on these four SAM surfaces according to a two‐step approach and the devices exhibit power conversion efficiency in the order of TQxD (8.3%) > TQx (8.0%) > PQxD (7.1%) > PQx (6.1%). With thiophene π‐extended conjugation unit in SAM structure, TQxD (4) exhibits the highest hole extraction rates, greatest hole mobilities, and slowest charge recombination to achieve great device performance of 8.3%, which is the current best result for SAM‐based TPSC ever reported. Furthermore, all devices except PQx shows great enduring stability for the performance retaining ≈90% of their original values for shelf storage over 1600 h.
Quinoxaline‐based X‐shaped molecules (1‐4) are designed and synthesized as p‐type self‐assembled monolayer (SAM) for tin perovskite solar cells (TPSC). SAM; TQxD (4) exhibits excellent device performance of 8.3%, and shows great enduring stability for the performance retaining ≈90% of their original values for shelf storage over 1600 h. This is the current best result for SAM‐based TPSC ever reported.
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.
We synthesized and characterized methylammonium (MA) mixed tri‐halide tin perovskites (MASnIBr2−xClx) for carbon‐based mesoscopic solar cells free of lead and hole‐transporting layers. Varied ...SnCl2/SnBr2 ratios yielded tin perovskites with three halides (I, Br, and Cl) co‐crystallized inside the tin‐perovskite. When the SnCl2 proportion was ≥50 % (x≥1), phase separation occurred to give MASnI3−yBry and MASnCl3−zBrz in the stoichiometric proportions of their precursors, confirmed by XRD. A device with MASnIBr1.8Cl0.2 (SnCl2=10 %) showed the best photovoltaic performance: JSC=14.0 mA cm−2, VOC=380 mV, FF=0.573, and PCE=3.1 %, and long‐term stability. Electrochemical impedance spectra (EIS) show superior charge recombination and dielectric relaxation properties for the MASnIBr1.8Cl0.2 cell. Transient PL decays showed the intrinsic problem of tin‐based perovskites with average lifetimes less than 100 ps.
Tin in: Stable tin perovskites co‐crystalized with three different halide elements (I, Br, and Cl) were produced by the reaction of methylammonium (MA) iodide with SnCl2/SnBr2 mixtures at ratios equal to or less than 25/75. The best device made of a carbon‐based mesoscopic electrode and MASnIBr1.8Cl0.2 exhibited a PCE of 3.1 %.
A new set of pyrrolopyrrole‐based (PPr) polymers incorporated with thioalkylated/alkylated bithiophene (SBT/BT) is synthesized and explored as hole‐transporting materials (HTMs) for Sn‐based ...perovskite solar cells (TPSCs). Three bithiophenyl spacers bearing the thioalkylated hexyl (SBT‐6), thioalkylated tetradecyl (SBT‐14), and tetradecyl (BT‐14) chains are utilized to examine the effect of the alkyl chain lengths. Among them, the TPSCs are fabricated using PPr‐SBT‐14 as HTMs through a two‐step approach by attaining a power conversion efficiency (PCE) of 7.6% with a remarkable long‐term stability beyond 6000 h, which has not been reported elsewhere for a non‐PEDOT:PSS‐based TPSC. The PPr‐SBT‐14 device is stable under light irradiation for 5 h in air (50% relative humidity) at the maximum power point (MPP). The highly planar structure, strong intramolecular S(alkyl)···S(thiophene) interactions, and extended π‐conjugation of SBT enable the PPr‐SBT‐14 device to outperform the standard poly(3‐hexylthiophene,‐2,5‐diyl (P3HT) and other devices. The longer thio‐tetradecyl chain in SBT‐14 restricts molecular rotation and strongly affects the molecular conformation, solubility, and film wettability over other polymers. Thus, the present study makes a promising dopant‐free polymeric HTM model for the future design of highly efficient and stable TPSCs.
A new series of hydrophobic conducting polymers containing pyrrolopyrrole (PPr) and thioalkylated/alkylated bithiophene (SBT/BT) moieties is designed and synthesized to serve as hole‐transport materials (HTMs) for tin‐based perovskite solar cells to attain a power conversion efficiency of 7.6% with shelf‐storage stability over 6000 h, which opens a new avenue for future development of non‐poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) HTMs with great performance and stability.
A graphene oxide (GO) film is functionalized with metal (Au) and metal‐oxide (MoOx) nanoparticles (NPs) as a hole‐extraction layer for high‐performance inverted planar‐heterojunction perovskite solar ...cells (PSCs). These NPs can increase the work function of GO, which is confirmed with X‐ray photoelectron spectra, Kelvin probe force microscopy, and ultraviolet photoelectron spectra measurements. The down‐shifts of work functions lead to a decreased level of potential energy and hence increased Voc of the PSC devices. Although the GO‐AuNP film shows rapid hole extraction and increased Voc, a Jsc improvement is not observed because of localization of the extracted holes inside the AuNP that leads to rapid charge recombination, which is confirmed with transient photoelectric measurements. The power conversion efficiency (PCE) of the GO‐AuNP device attains 14.6%, which is comparable with that of the GO‐based device (14.4%). In contrast, the rapid hole extraction from perovskite to the GO‐MoOx layer does not cause trapping of holes and delocalization of holes in the GO film accelerates rapid charge transfer to the indium tin oxide substrate; charge recombination in the perovskite/GO‐MoOx interface is hence significantly retarded. The GO‐MoOx device consequently shows significantly enhanced Voc and Jsc, for which its device performance attains PCE of 16.7% with great reproducibility and enduring stability.
Two functional graphene oxide (GO) films are fabricated by coating gold nanoparticles and molybdenum oxide nanoparticles (GO‐MoOx) on the GO sheets to serve as p‐contact electrode for inverted planar perovskite solar cells. The GO‐MoOx device forms delocalized holes to retard charge recombination and atains power conversion efficiency of 16.7%.
