Enhanced charge carrier mobility and lifetime suppress hysteresis and improve efficiency in planar perovskite solar cells (original) (raw)
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Perovskite Solar Cells: Progress and Advancements
Organic–inorganic hybrid perovskite solar cells (PSCs) have emerged as a new class of optoelectronic semiconductors that revolutionized the photovoltaic research in the recent years. The perovskite solar cells present numerous advantages include unique electronic structure, bandgap tunability, superior charge transport properties, facile processing, and low cost. Perovskite solar cells have demonstrated unprecedented progress in efficiency and its architecture evolved over the period of the last 5–6 years, achieving a high power conversion efficiency of about 22% in 2016, serving as a promising candidate with the potential to replace the existing commercial PV technologies. This review discusses the progress of perovskite solar cells focusing on aspects such as superior electronic properties and unique features of halide perovskite materials compared to that of conventional light absorbing semiconductors. The review also presents a brief overview of device architectures, fabrication methods, and interface engineering of perovskite solar cells. The last part of the review elaborates on the major challenges such as hysteresis and stability issues in perovskite solar cells that serve as a bottleneck for successful commercialization of this promising PV technology.
Temperature-dependent hysteresis effects in perovskite-based solar cells
J. Mater. Chem. A, 2015
This journal is Staircase voltage sweep measurements were performed on 1 perovskite solar cell at 250 K, 300 K, and 360 K. Time-2 dependent photocurrent data reveal the complexity of the 3 signal that cannot be described by a simple mono-4 exponential function suggesting multiple charging-5 discharging processes are responsible for the complex 6 hysteresis behavior. 7 Organo-lead-halide perovskite (OHP) based solar cells were 8 reported to achieve energy-to-electricity power conversion 9 efficiency (PCE) as high as ~19.3%, 1-8 which combined with 10 reported methods for low-cost, flexible, and large-area solar cell 11 fabrication such as ultra-sonic spray-coating 9 and printing 12 technology 10 makes OHP cell technology amenable to scaling up 13 to production levels. 2, 5 The potential toxic effects of Pb has been 14 pointed out. Alternatives or solutions have been proposed such as 15 Pb-free perovskite based solar cells, encapsulation, and Pb 16 recycling. 11-14 17 Methylammonium (MA) lead iodide (CH 3 NH 3 PbI 3 ), the most 18 commonly employed material in halide perovskite solar cells, was 19 reported to have both high absorption coefficient (direct bandgap 20 of ~1.55 eV) and high mobilities for electrons (7.5 cm 2˜V 1˜s 1 ) 21 and holes (12.5 66 cm 2˜V 1˜s 1 ) resulting in long carrier diffusion 22 capacitance effect was hypothesized to be originated from (i) the 47 ferroelectricity or polarization of the perovskite layer; (ii) contact 48 conductivity; (iii) diffusion of excess ion as interstitial defects; 49 and/or (iv) trapping/de-trapping of charge carriers. 18-20, 27 50 In this work, we performed staircase voltage sweep 51 measurements 18-20 at three different temperatures of 250 K, 52 300 K, and 360 K to quantify the photocurrent transient 53 behavior on the complete perovskite cell composed of FTO/c-54 TiO 2 /perovskite/spiro-MeOTAD/Au where FTO stands for 55 fluorine doped tin oxide. The hole-collection was through the 56 spiro-MeOTAD hole transport layer (HTL). Our photocurrent 57 data suggest that multiple processes are responsible for the 58 complex transient behavior. Furthermore, solar cell properties 59 can be altered significantly by the changes in environmental 60 conditions such as humidity and temperature. 28-31 Thus, 61 device performance characterization of perovskite cells under 62 various conditions is of paramount importance. Also it can 63 provide a fundamental understanding of the charging-64 discharging processes in perovskite cells if studied under 65 controlled environment (temperature, humidity, gas 66 environment). 31 The temperature dependent studies of the 67 steady-state I-V curves provided the trends of open-circuit 68 voltage (V oc ), short-circuit current (I sc ), and fill factor (FF) 69 electrical parameters as a function of temperature shedding 70 light on the physical processes taking place within the layers 71 of perovskite solar cell. These results highlight the 72 importance to establish a protocol for precise and artifact-free 73 evaluation of perovskite solar cells. 74 The perovskite films in this work were prepared from 75 MAI and PbCl 2 precursors according to standard literature 76 procedure reported elsewhere. 32-34 Detailed sample 77 preparation was described in the supporting information. 78 Sample characterization by X-ray diffraction (XRD) and 79 scanning electron microscopy (SEM) are shown in Fig. 1.
Solar Energy Materials and Solar Cells, 2020
In this report, a modeling approach is employed to study the effect of the grain boundaries (GBs) and their electronic activity on the performance parameters of the perovskite solar cells (PSCs). Our model is based on the 1-dimensional drift-diffusion framework to engage the electron (hole) defects formed in the GBs and the GB's location through the perovskite layer. Power conversion efficiency (PCE) of the PSC is optimized with regards to the perovskite layer thickness, GBs location and perovskite layer band offset with GBs layer. The results shows that the location or the distribution of the GBs can vary the PCE of PSCs from 12% to around 21%, thereby making proper morphology engineering and passivation of GBs is a chief requirement for achieving high efficiency. PCEs larger than 21% require GB defect densities below 10 15 cm À 2. It is demonstrated that the band offset of about 100 meV with GB width of 1 nm could effectively suppress the negative impact of the GBs throughout the entire perovskite layer. Interestingly, GBs location at closer points to electron transport layer (ETL)/perovskite interface may give rise to higher PCEs, however, relatively stronger hysteresis in current values is observed. The results here provide insight into the effect of the GBs location and their corresponding type of defects on the hysteresis and the PSC performance and opens up new horizons to find solutions for current PSC's shortcomings.
Applied Materials Today, 2018
The rapid improvements of perovskite solar cells since its inception has been associated the advancements in the perovskite layer itself and the efficiency of the hole transport materials (HTM). As a potential for future energy applications, recording high power conversion efficiency of perovskite solar cells has instigated the search for a more scalable production method with the usage of cheap and nontoxic precursors. By applying the insights from dye-sensitized solar cells fabrications methods, perovskite solar cells possess the ability to improve at a remarkable pace and the potential to be applied directly into the current systems without requiring new arrangements. Deposition of the perovskite layer onto the substrate has been a struggle particularly in the crystallinity, surface defects, toxicity and stability issues. Prerequisite to HTM includes high conductivity, diffusion length and compatibility with neighbouring layers. In this review paper, we will highlight two approaches that able to improve the perovskite solar cells performance namely crystallinity and morphological control of the perovskite and development of hole transporting materials for planar and inverted perovskite solar cells.
Highly efficient planar perovskite solar cells through band alignment engineering
Energy Environ. Sci., 2015
The simplification of perovskite solar cells (PSCs), by replacing the mesoporous electron selective layer (ESL) with a planar one, is advantageous for large-scale manufacturing. PSCs with a planar TiO 2 ESL have been demonstrated, but these exhibit unstabilized power conversion efficiencies (PCEs). Herein we show that planar PSCs using TiO 2 are inherently limited due to conduction band misalignment and demonstrate, with a variety of characterization techniques, for the first time that SnO 2 achieves a barrier-free energetic configuration, obtaining almost hysteresis-free PCEs of over 18% with record high voltages of up to 1.19 V.
Unraveling film transformations and device performance of planar perovskite solar cells
Nano Energy, 2015
High performance (415%) organometaltrihalide based solar cells have been demonstrated in recent years to be a promising candidate for low cost photovoltaics and have attracted significant attention in the photovoltaic community. Planar thin film perovskite solar cells, which are more easily fabricated, provide a great platform to investigate the perovskite film properties. Until now, many of the properties of perovskite thin films remain unexplored and the link between film properties and device performances is in need of investigation to further boost the efficiencies of these devices. Here, film transformation of perovskite materials is demonstrated as a critical factor to reach high performance in planar heterojunction CH 3 NH 3 PbI 3 À x Cl x solar cells. Reaction induced secondary phases can be observed and carefully controlled by tuning the processing conditions during film formation. The properties of CH 3 NH 3 PbI 3 À x Cl x films are investigated and a possible formation pathway is proposed. It is shown that the high performance devices are attainable with a small portion of secondary phases coexisting with CH 3 NH 3 PbI 3 film and power conversion efficiencies of up to 14% are achieved. The correlations between the phases present, device performance and physical properties are discussed to identify the role of the secondary phases in CH 3 NH 3 PbI 3 À x Cl x material.
Nano Research, 2014
We demonstrate that charge carrier diffusion lengths of two classes of perovskites, CH 3 NH 3 PbI 3-x Cl x and CH 3 NH 3 PbI 3 , are both highly sensitive to film processing conditions and optimal processing procedures are critical to preserving the long carrier diffusion lengths of the perovskite films. This understanding, together with the improved cathode interface using bilayer-structured electron transporting interlayers of [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM)/ZnO, leads to the successful fabrication of highly efficient, stable and reproducible planar heterojunction CH 3 NH 3 PbI 3-x Cl x solar cells with impressive power-conversion efficiencies (PCEs) up to 15.9%. A 1-square-centimeter device yielding a PCE of 12.3% has been realized, demonstrating that this simple planar structure is promising for large-area devices.
Universal Approach toward Hysteresis-Free Perovskite Solar Cell via Defect Engineering
Journal of the American Chemical Society, 2018
Organic-inorganic halide perovskite is believed to be a potential candidate for high efficiency solar cells because power conversion efficiency (PCE) was certified to be more than 22%. Nevertheless, mismatch of PCE due to current density (J)-voltage (V) hysteresis in perovskite solar cells is an obstacle to overcome. There has been much lively debate on the origin of J-V hysteresis; however, effective methodology to solve the hysteric problem has not been developed. Here we report a universal approach for hysteresis-free perovskite solar cells via defect engineering. A severe hysteresis observed from the normal mesoscopic structure employing TiO2 and spiro-MeOTAD is almost removed or does not exist upon doping the pure perovskites, CH3NH3PbI3 and HC(NH2)2PbI3, and the mixed cation/anion perovskites, FA0.85MA0.15PbI2.55Br0.45 and FA0.85MA0.1Cs0.05PbI2.7Br0.3, with potassium iodide. Substantial reductions in low-frequency capacitance and bulk trap density are measured from the KI-dope...
Latvian Journal of Physics and Technical Sciences, 2017
Organometal halide perovskites are promising materials for lowcost, high-efficiency solar cells. The method of perovskite layer deposition and the interfacial layers play an important role in determining the efficiency of perovskite solar cells (PSCs). In the paper, we demonstrate inverted planar perovskite solar cells where perovskite layers are deposited by two-step modified interdiffusion and one-step methods. We also demonstrate how PSC parameters change by doping of charge transport layers (CTL). We used dimethylsupoxide (DMSO) as dopant for the hole transport layer (PEDOT:PSS) but for the electron transport layer [6,6]-phenyl CThe highest main PSC parameters (