Project description:Compositional engineering has been used to overcome difficulties in fabricating high-quality phase-pure formamidinium perovskite films together with its ambient instability. However, this comes alongside an undesirable increase in bandgap that sacrifices the device photocurrent. Here we report the fabrication of phase-pure formamidinium-lead tri-iodide perovskite films with excellent optoelectronic quality and stability. Incorporation of 1.67?mol% of 2D phenylethylammonium lead iodide into the precursor solution enables the formation of phase-pure formamidinium perovskite with an order of magnitude enhanced photoluminescence lifetime. The 2D perovskite spontaneously forms at grain boundaries to protect the formamidinium perovskite from moisture and suppress ion migration. A stabilized power conversion efficiency (PCE) of 20.64% (certified stabilized PCE of 19.77%) is achieved with a short-circuit current density exceeding 24?mA?cm-2 and an open-circuit voltage of 1.130?V, corresponding to a loss-in-potential of 0.35?V, and significantly enhanced operational stability.
Project description:This paper presents the results of a combined experimental and analytical/computational study of the effects of pressure on photoconversion efficiencies of perovskite solar cells (PSCs). First, an analytical model is used to predict the effects of pressure on interfacial contact in the multilayered structures of PSCs. The PSCs are then fabricated before applying a range of pressures to the devices to improve their interfacial surface contacts. The results show that the photoconversion efficiencies of PSCs increase by ~40%, for applied pressures between 0 and ~7?MPa. However, the photoconversion efficiencies decrease with increasing pressure beyond ~7?MPa. The implications of the results are discussed for the fabrication of efficient PSCs.
Project description:Humidity is known to be inimical to the halide perovskites and thus typically avoided during fabrication. The poor fundamental understanding of chemical interactions between water and the precursors hampers the further development of perovskite fabrication in ambient atmosphere. Here, we disclose a key finding that the ambient water could promote the formation of lead complexes, which when uncontrolled would make their way into large intermediate fibrillar crystallites and thus discontinuous perovskite films unfavorable for photovoltaics among others. To counter this effect, a prenucleation strategy is proposed, which embodies the controlled burst of profuse intermediate nuclei. Consequently, we are able to obtain a compact and uniform perovskite layer, which affords high efficiency perovskite solar cells. More excitingly, the solar cells show high performance uniformity, demonstrating the distinctive advantages of our prenucleation strategy. This work sheds light on developing reliable and cost-effective fabrication methods for industrial production of perovskite solar cells.
Project description:Poor stability of organic-inorganic halide perovskite materials in humid condition has hindered the success of perovskite solar cells in real applications since controlled atmosphere is required for device fabrication and operation, and there is a lack of effective solutions to this problem until now. Here we report the use of lead (II) thiocyanate (Pb(SCN)2) precursor in preparing perovskite solar cells in ambient air. High-quality CH3NH3PbI3-x(SCN)x perovskite films can be readily prepared even when the relative humidity exceeds 70%. Under optimized processing conditions, we obtain devices with an average power conversion efficiency of 13.49% and the maximum efficiency over 15%. In comparison with typical CH3NH3PbI3-based devices, these solar cells without encapsulation show greatly improved stability in humid air, which is attributed to the incorporation of thiocyanate ions in the crystal lattice. The findings pave a way for realizing efficient and stable perovskite solar cells in ambient atmosphere.
Project description:Intermediate phase is considered an important aspect to deeply understand the crystallization procedure in the growth of high-quality perovskite layers by an anti-solvent technique. However, the moisture influence on the intermediate phase formation is not clear in air conditions as yet. In this work, pure (FA0.2MA1.8)Pb3X8(DMSO·DMF) intermediate phase was obtained in as-prepared perovskite film by spin-coating the precursor of co-solvent (DMSO and DMF) in an ambient air (RH20-30%). Moreover, the appropriate quantity of ethyl acetate (C4H8O2, EA) also controls the formation of pure intermediate phase. The uniform and homogeneous perovskite film was obtained after annealing this intermediate film. Therefore, the best power conversion efficiency (PCE) of perovskite solar cells (PSCs) is 16.24% with an average PCE of 15.53%, of which almost 86% of its initial PCE was preserved after 30 days in air conditions. Besides, the steady-state output efficiency ups to 15.38% under continuous illumination. In addition, the PCE of large area device (100 mm2) reaches 11.11% with a little hysteresis effect. This work would give an orientation for PSCs production at the commercial level, which could lower the cost of fabricating the high efficiency PSCs.
Project description:Dye-sensitized solar cells are promising candidates for low-cost indoor power generation applications. However, they currently suffer from complex fabrication and stability issues arising from the liquid electrolyte. Consequently, the so-called zombie cell was developed, in which the liquid electrolyte is dried out to yield a solid through a pinhole after cell assembly. We report a method for faster, simpler, and potentially more reliable production of zombie cells through direct and rapid drying of the electrolyte on the working electrode prior to cell assembly, using an iodide-triiodide redox couple electrolyte as a basis. These "rapid-zombie" cells were fabricated with power conversion efficiencies reaching 5.0%, which was larger than the 4.5% achieved for equivalent "slow" zombie cells. On a large-area cell of 15.68 cm2, over 2% efficiency was achieved at 0.2 suns. After 12 months of dark storage, the "rapid-zombie" cells were remarkably stable and actually showed a moderate increase in average efficiencies.
Project description:We herein demonstrate n-i-p-type planar heterojunction perovskite solar cells employing spin-coated ZnO nanoparticles modified with various alkali metal carbonates including Li2CO3, Na2CO3, K2CO3 and Cs2CO3, which can tune the energy band structure of ZnO ETLs. Since these metal carbonates doped on ZnO ETLs lead to deeper conduction bands in the ZnO ETLs, electrons are easily transported from the perovskite active layer to the cathode electrode. The power conversion efficiency of about 27% is improved due to the incorporation of alkali carbonates in ETLs. As alternatives to TiO2 and n-type metal oxides, electron transport materials consisting of doped ZnO nanoparticles are viable ETLs for efficient n-i-p planar heterojunction solar cells, and they can be used on flexible substrates via roll-to-roll processing.
Project description:The breakthrough of organometal halide perovskite solar cells (PSCs) based on mesostructured composites is regarded as a viable member of next generation photovoltaics. In high efficiency PSCs, it is crucial to finely optimize the charge dynamics and optical properties matching between the perovskites and electron transporting materials to relax the trade-off between the optical and electrical requirements. Here, a simple antipolar route with H2O as the additive is proposed to prepare hierarchical electron transporting layers to boost the efficiency of dopant-free PSCs. The photovoltaic performance of the PSCs is enhanced owing to increased light-scattering, improved Ostwald ripening, and photo-generated electron extraction. Optimization of the H2O addition enables a valid power conversion efficiency of 19.9% (reverse scan: 20.02%) to be achieved. The device can retain more than 90% of its initial performance after storage in air more than 30 days. These results are inspiring in that they present that a mesoporous transporting layer could be easily re-constructed to hierarchical architecture by the antipolar method to further improve the performance of PSCs.
Project description:Formamidinium lead iodide (FAPbI3) is a newly developed hybrid perovskite that potentially can be used in high-efficiency solution-processed solar cells. Here, the temperature-dependent dynamic optical properties of three types of FAPbI3 perovskite films (fabricated using three different precursor systems) are comparatively studied. The time-resolved photoluminescence (PL) spectra reveal that FAPbI3 films made from the new precursor (a mixture of formamidinium iodide and hydrogen lead triiodide) exhibit the longest lifetime of 439 ns at room temperature, suggesting a lower number of defects and lower non-radiative recombination losses compared with FAPbI3 obtained from the other two precursors. From the temperature-dependent PL spectra, a phase transition in the films is clearly observed. Meanwhile, exciton-binding energies of 8.1 and 18 meV for the high- and low-temperature phases are extracted, respectively. Importantly, the PL spectra for all of the samples show a single peak at room temperature, whereas at liquid-helium temperature the emission features two peaks: one in higher energy displaying a fast decay (0.5 ns) and a second red-shifted peak with a decay of up to several microseconds. These two emissions, separated by ~18 meV, are attributed to free excitons and bound excitons with singlet and triplet characters, respectively.
Project description:For the perovskite solar cells with formamidinium lead iodide (FAPbI3) as a light harvester, cesium ions (Cs+) can be used to stabilize the perovskite crystal structure of FAPbI3. However, the incorporation of Cs+ ions usually reduces the grain size and degrades the crystallization of FAPbI3 layers, and this is harmful to the photovoltaic performance of solar cells. In this work, we incorporate Cs+ ions into FAPbI3 layers using the interfacial doping method, which is different from the mixed solution doping method in previous reports. Elemental analysis indicates that Cs+ dopants cannot be detected at the outer surfaces of perovskite layers, and the majority of Cs+ dopants should be localized in the vicinity of TiO2/perovskite interfaces, which is remarkably different from the distribution of Cs+ dopants in the perovskite layers prepared using the mixed solution doping method. It is found that interfacial doping method can avoid the blue shift of the light absorption edge and can improve the crystallization of FAPbI3 layers. For the optimized conditions, Cs x FA1-x PbI3 solar cells prepared using the interfacial doping method achieve a power conversion efficiency (PCE) of 17.1%, which is better than the PCE of Cs x FA1-x PbI3 devices prepared using the mixed solution doping method.