Using Solvent Vapor Annealing for the Enhancement of the Stability and Efficiency of Monolithic Hole-conductor-free Perovskite Solar Cells (original) (raw)
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Advanced Materials, 2018
high carrier mobility. [2,3] A typical perovskite has a 3D lattice structure with a formula of ABX 3 where A + is composed of organic (CH 3 NH 3 + (MA +) or CH 3 (NH 2) 2 + (FA +)) or inorganic (cesium + (Cs +) or rubidium + (Rb +)) cation, B 2+ is the divalent metal (Pb 2+ or Sn 2+), and X − is the halide (Cl − , Br − , or I −). [2,4] To realize commercial applications, the long-term stability issues such as durability under humid, thermal, and light-soaking conditions should be further investigated and improved. [5] Most annoyingly, the perovskite thin film is quite sensitive to moisture and oxygen, resulting in degradation under atmosphere. The low formation energy of the perovskite structures tends to hydrolyze in the presence of moisture. [6] One of the methods to stabilize halide perovskite is to use the layered structure with 2D perovskites, the so-called Ruddlesden-Popper layered perovskites, where larger hydrophobic cation acts as a spacer to isolate the 3D MAPbI 3. [7-12] The general formula of Ruddlesden-Popper perovskites is defined as A′ 2 A n−1 B n X 3n+1 , where n is an integer between 1 and ∞ and A′ + is large-sized cation (typically ammonium-based cation such as phenyl ethylammonium (PEA), [10] polyethylenimine (PEI), [13] n-butylammine (BA), [14] cyclopropylamine (CA), [15] octadecylamine (OA), [16] or ammoniumvaleric The fabrication of multidimensional organometallic halide perovskite via a lowpressure vapor-assisted solution process is demonstrated for the first time. Phenyl ethyl-ammonium iodide (PEAI)-doped lead iodide (PbI 2) is first spincoated onto the substrate and subsequently reacts with methyl-ammonium iodide (MAI) vapor in a low-pressure heating oven. The doping ratio of PEAI in MAI-vapor-treated perovskite has significant impact on the crystalline structure, surface morphology, grain size, UV-vis absorption and photoluminescence spectra, and the resultant device performance. Multiple photoluminescence spectra are observed in the perovskite film starting with high PEAI/ PbI 2 ratio, which suggests the coexistence of low-dimensional perovskite (PEA 2 MA n−1 Pb n I 3n+1) with various values of n after vapor reaction. The dimensionality of the as-fabricated perovskite film reveals an evolution from 2D, hybrid 2D/3D to 3D structure when the doping level of PEAI/PbI 2 ratio varies from 2 to 0. Scanning electron microscopy images and Kelvin probe force microscopy mapping show that the PEAI-containing perovskite grain is presumably formed around the MAPbI 3 perovskite grain to benefit MAPbI 3 grain growth. The device employing perovskite with PEAI/PbI 2 = 0.05 achieves a champion power conversion efficiency of 19.10% with an open-circuit voltage of 1.08 V, a current density of 21.91 mA cm −2 , and a remarkable fill factor of 80.36%. Perovskite Solar Cells Organic-inorganic hybrid perovskite materials have attracted numerous attentions in solar energy conversion and various optoelectronic applications [1] due to their long carrier diffusion length, high absorption coefficients in the visible range, and The ORCID identification number(s) for the author(s) of this article can be found under
Low-Temperature Solution-Processed Perovskite Solar Cells with High Efficiency and Flexibility
ACS Nano, 2014
Perovskite compounds have attracted recently great attention in photovoltaic research. The devices are typically fabricated using condensed or mesoporous TiO 2 as the electron transport layer and 2,2 0 7,7 0 -tetrakis-(N,N-dip-methoxyphenylamine)9,9 0spirobifluorene as the hole transport layer. However, the hightemperature processing (450°C) requirement of the TiO 2 layer could hinder the widespread adoption of the technology. In this report, we adopted a low-temperature processing technique to attain highefficiency devices in both rigid and flexible substrates, using device structure substrate/ITO/PEDOT:PSS/CH 3 NH 3 PbI 3Àx Cl x /PCBM/Al, where PEDOT:PSS and PCBM are used as hole and electron transport layers, respectively. Mixed halide perovskite, CH 3 NH 3 PbI 3Àx Cl x , was used due to its long carrier lifetime and good electrical properties. All of these layers are solution-processed under 120°C. Based on the proposed device structure, power conversion efficiency (PCE) of 11.5% is obtained in rigid substrates (glass/ITO), and a 9.2% PCE is achieved for a polyethylene terephthalate/ITO flexible substrate.
Sequentially Vapor-Grown Hybrid Perovskite for Planar Heterojunction Solar Cells
High-quality and reproducible perovskite layer fabrication routes are essential for the implementation of efficient planar solar cells. Here, we introduce a sequential vapor-processing route based on physical vacuum evaporation of a PbCl 2 layer followed by chemical reaction with methyl-ammonium iodide vapor. The demonstrated vapor-grown perovskite layers show compact, pinhole-free, and uniform microstructure with the average grain size of~320 nm. Planar heterojunction perovskite solar cells are fabricated using TiO 2 and spiro-OMeTAD charge transporting layers in regular n-i-p form. The devices exhibit the best efficiency of 11.5% with small deviation indicating the high uniformity and reproducibility of the perovskite layers formed by this route.
Efficient planar heterojunction perovskite solar cells by vapour deposition
Many different photovoltaic technologies are being developed for large-scale solar energy conversion 1-4 . The wafer-based firstgeneration photovoltaic devices 1 have been followed by thin-film solid semiconductor absorber layers sandwiched between two charge-selective contacts 3 and nanostructured (or mesostructured) solar cells that rely on a distributed heterojunction to generate charge and to transport positive and negative charges in spatially separated phases 4-6 . Although many materials have been used in nanostructured devices, the goal of attaining high-efficiency thinfilm solar cells in such a way has yet to be achieved 7 . Organometal halide perovskites have recently emerged as a promising material for high-efficiency nanostructured devices . Here we show that nanostructuring is not necessary to achieve high efficiencies with this material: a simple planar heterojunction solar cell incorporating vapour-deposited perovskite as the absorbing layer can have solar-to-electrical power conversion efficiencies of over 15 per cent (as measured under simulated full sunlight). This demonstrates that perovskite absorbers can function at the highest efficiencies in simplified device architectures, without the need for complex nanostructures.
Solar Energy Materials and Solar Cells, 2017
The formation of a dense and uniform perovskite film with large grain is an important factor for getting excellent device performance. Here, we report an optimized solvent-assisted crystallization procedure followed by a delayed annealing for easy and reproducible fabrications of perovskite solar cells with a hybrid mesoscopic configuration. The working electrode contains a mesoporous TiO 2 scaffold layer of 100 nm deposited on FTO substrate with a thin TiO 2 blocking layer. The devices in this study were assembled using all commercially available materials without any extensive modification. Formation of uniform and pin-hole free perovskite nanocrystals with film thickness 200 nm on top of the scaffold layer was achieved via an optimized solventassisted crystallization method. A much smoother perovskite layer was achieved with a delayed annealing for a certain period. The best performing device was obtained at the annealing delayed for 60 min, giving the power conversion efficiency 16.9% with an average value 15.4% obtained from 60 devices.
Advanced Energy Materials, 2018
layers and charge selecting buffer layers (i.e., electron-transporting layer (ETL) and hole-transporting layer (HTL)) are the key elements that determine the performance of PSCs. [5,8-12] The current state-of-the-art performance of PSCs is attained using high-temperature (≈500 °C)-sintered mesoporous TiO 2 as ETL, and spiro-OMeTAD as HTL. [1,2,13,14] In this type of PSC, the TiO 2 ETL is the process temperature determining material, while the perovskite active layers and HTLs can be prepared at relatively lower temperature (<150 °C). [2,4,5,10,15] To realize the PSC fabrication at lower temperature using various substrates, such as flexible plastics, [1,15,16] much effort has been made to develop high-performance low-temperature-processable ETLs for PSCs. [4,17-21] ZnO is a promising ETL candidate for PSCs because of easy solution processability, good optoelectronic properties, and appropriate work function. [18,19,22-30] Solution-processed ZnO has been successfully employed as ETL for other thin film solar cells such as organic photovoltaic devices and colloidal quantum dot solar cells. [23,26,29-33] Although there are some
High-Efficiency Solution-Processed Planar Perovskite Solar Cells with a Polymer Hole Transport Layer
Advanced Energy Materials, 2014
In this work we demonstrate a high-effi ciency solutionprocessed inverted CH 3 NH 3 PbI 3 perovskite solar cell, which is free of PEDOT:PSS and high-temperature processed metal oxides . We use poly[ N , N ′-bis(4-butylphenyl)-N , N ′bis(phenyl)benzidine] (poly-TPD) as the HTL and electron blocking layer for the perovskite cells. In previous reports, poly-TPD was used as an HTL in vacuum deposited perovskite solar cells. Here, the perovskite fi lm was formed by sequential deposition of lead iodide (PbI 2 ) and methyl ammonium iodide (CH 3 NH 3 I). We found that the resulting fi lm consisted of large crystallites with a complete coverage on the poly-TPD surface, and the average effi ciency of the fi nal devices reach a value of 13.8% and a maximum value as high as 15.3%.
Advanced Science
Organic–inorganic perovskite solar cells (PSCs) have achieved great attention due to their expressive power conversion efficiency (PCE) up to 25.7%. To improve the photovoltaic performance of PSCs, interface engineering between the perovskite and hole transport layer (HTL) is a widely used strategy. Following this concept, benzyl trimethyl ammonium chlorides (BTACls) are used to modify the wet chemical processed perovskite film in this work. The BTACl‐induced low dimensional perovskite is found to have a bilayer structure, which efficiently decreases the trap density and improves the energy level alignment at the perovskite/HTL interface. As a result, the BTACl‐modified PSCs show an improved PCE compared to the control devices. From device modeling, the reduced charge carrier recombination and promoted charge carrier transfer at the perovskite/HTL interface are the cause of the open‐circuit (Voc) and fill factor (FF) improvement, respectively. This study gives a deep understanding f...