Effect Of Hole Transport Layer Research Articles

Unraveling the Energy Landscape and Energy Funneling Modulated by Hole Transport Layer for Highly Efficient Perovskite LEDs

AbstractPrevious reports have demonstrated significant effects of hole transport layer (HTL) on the morphology of quasi‐2 dimensional (2D) perovskites, hole injection, and interfacial defect density. However, the effects of HTL on energy landscape and energy funneling of quasi‐2D perovskites have not been revealed so far. Herein, the PEA2Csn−1PbnBr3n+1 perovskite films are fabricated on four types of HTLs including poly(9‐vinylcarbazole):poly(ethylene oxide) (PVK:PEO), PVK, poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), and nickel oxide (NiOx). The steady‐state and transient absorption spectroscopies reveal that the energy landscape and energy funneling of quasi‐2D perovskites vary significantly on different HTLs. All domains with n = 1, 2, 3, and higher order (n ≥ 4) are formed with desired population ratios on the PVK:PEO HTL, leading to the most efficient energy funneling. Furthermore, the interfacial passivation effect of PEO on the energy funneling process is studied. The light‐emitting diodes (LEDs) based on PEA2Csn−1PbnBr3n+1 and PVK:PEO (with an optimized ratio of 5.3:0.7 w/w) HTL result in a maximum luminescence of ≈23 110 cd m–2 and maximum external quantum efficiency of ≈11.5%, respectively. This is the best performance reported so far using pure PEA2Csn−1PbnBr3n+1 without perovskite composition modifications. This study provides new insights into the HTL for the development of highly efficient quasi‐2D perovskite LEDs.

Numerical simulation of highly efficient lead-free perovskite layers for the application of all-perovskite multi-junction solar cell

The numerical simulation of lead-free perovskite cesium tin germanium halide (CsSnGeI3) and methyl ammonium germanium halide (CH3NH3GeI3) solar cells have been performed. It has been elucidated from the numerical simulation that as compare to the CH3NH3GeI3 based structure, CsSnGeI3 based structure depicts better photovoltaic performance under constant illumination condition. To enhance the device photovoltaic performance, the effects of different hole transport layer (HTL), defect density of the absorber layer, metal work function and the effect of temperature has been studied. In the present investigation, the effect of hole transport layers are analyzed by correlating the built-in voltage (Vbi) with the open circuit voltage (VOC). It has been obtained from the simulation results, that Vbi has a significant impact on VOC as the higher Vbi corresponds to the highest VOC. Moreover, the effect of defect density and metal work function is also studied. It is obtained from the simulation results, that the optimum defect density is found to be 1 × 1014 cm−3 and metal work function should be greater than or equal to 5 eV for both lead-free CH3NH3GeI3 and CsSnGeI3 based perovskite layer. Furthermore, to suggest possible lead-free alternatives for all-perovskite two-terminal multi-junction solar cell, an attempt is made to match the current of bottom perovskite layer i.e., CsSnGeI3 based perovskite layer to the top perovskite layer i.e., CH3NH3GeI3 based perovskite layer. To attain the current matching for bottom perovskite layer (CsSnGeI3 based perovskite layer) to top perovskite layer (CH3NH3GeI3 based perovskite layer), the bottom perovskite sub cell is fed with the filtered spectrum which is obtained by transmission from top electrode. After, the realization of current matching the short circuit current density of CsSnGeI3 based perovskite layer drops from 25.75 mA/cm2 to 15.32 mA/cm2 which is similar to CH3NH3GeI3 based perovskite absorber layer. In addition, it has been obtained from literature, that both the perovskite layers can be fabricated using solution–processing low-temperature technology. Hence, the numerical study suggests the possible alternatives for wide and narrow bandgap perovskite layers for the application to obtain highly efficient lead-free all-perovskite multi-junction solar cells.

Analysis of the role of hole transport layer materials to the performance of perovskite solar cell

Research in solar cells is needed to maximize Indonesia’s vast solar potential that can reach up to 207.898 MW with an average radiation of 4.8 kWh/m2/day. Organometallic perovskite solar cells (PSCs) have gained immense attention due to their rapid increase in efficiency and compatibility with low-cost fabrication methods. Understanding the role of hole transport layer is very important to obtain highly efficient PSCs. In this work, we studied the effect of Hole Transport Layer (HTL) to the performance of perovskite solar cell. The devices with HTL exhibit substantial increase in power conversion efficiency, open circuit voltage and short circuit current compared to the device without HTL. The best performing device is PSC with CuSCN as HTL layer, namely Voc of 0.24, Isc of 1.79 mA, 0.27 FF and efficiency of 0.09%.

The effect of hole transport layer on the thermal stability of inverted polymer solar cells

In this article, the effect of hole transport layer (HTL) on the thermal stability of inverted polymer solar cells (PSCs) consisting of the blend of poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl-C60 butyric acid methyl ester fullerene derivative (PCBM) as active layer (AL) is investigated. The two conventional HTLs, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and MoO3, were used in this study to demonstrate the effect of HTLs on the thermal stability of PSCs. The inverted devices were heated at 80–110 °C as accelerated test for different time intervals to illustrate the temporal variation of performance. The different temporal behaviors during (1) metastable period and (2) thermally unstable period are described here. Moreover, the effect of photoactive film thickness on the thermal stability of devices based on the two HTLs was considered. This study shows that the spin- and spray-coated devices exhibit different characteristics of thermal stability for the PSCs with MoO3 and PEDOT:PSS as HTLs, respectively. The temporal behavior caused by the effect of HTL during the thermally-unstable period is quantitatively studied. This study could provide vital information required to develop high durability in commercial PSCs.

Recent Advances in the Inverted Planar Structure of Perovskite Solar Cells.

Inorganic-organic hybrid perovskite solar cells research could be traced back to 2009, and initially showed 3.8% efficiency. After 6 years of efforts, the efficiency has been pushed to 20.1%. The pace of development was much faster than that of any type of solar cell technology. In addition to high efficiency, the device fabrication is a low-cost solution process. Due to these advantages, a large number of scientists have been immersed into this promising area. In the past 6 years, much of the research on perovskite solar cells has been focused on planar and mesoporous device structures employing an n-type TiO2 layer as the bottom electron transport layer. These architectures have achieved champion device efficiencies. However, they still possess unwanted features. Mesoporous structures require a high temperature (>450 °C) sintering process for the TiO2 scaffold, which will increase the cost and also not be compatible with flexible substrates. While the planar structures based on TiO2 (regular structure) usually suffer from a large degree of J-V hysteresis. Recently, another emerging structure, referred to as an "inverted" planar device structure (i.e., p-i-n), uses p-type and n-type materials as bottom and top charge transport layers, respectively. This structure derived from organic solar cells, and the charge transport layers used in organic photovoltaics were successfully transferred into perovskite solar cells. The p-i-n structure of perovskite solar cells has shown efficiencies as high as 18%, lower temperature processing, flexibility, and, furthermore, negligible J-V hysteresis effects. In this Account, we will provide a comprehensive comparison of the mesoporous and planar structures, and also the regular and inverted of planar structures. Later, we will focus the discussion on the development of the inverted planar structure of perovskite solar cells, including film growth, band alignment, stability, and hysteresis. In the film growth part, several methods for obtaining high quality perovskite films are reviewed. In the interface engineering parts, the effect of hole transport layer on subsequent perovskite film growth and their interface band alignment, and also the effect of electron transport layers on charge transport and interface contact will be discussed. As concerns stability, the role of charge transport layers especially the top electron transport layer in the devices stability will be concluded. In the hysteresis part, possible reasons for hysteresis free in inverted planar structure are provided. At the end of this Account, future development and possible solutions to the remaining challenges facing the commercialization of perovskite solar cells are discussed.

Characterization of Organic Thin Film Solar Cells of PCDTBT : PC71BM Prepared by Different Mixing Ratio and Effect of Hole Transport Layer

The organic thin film solar cells (OTFSCs) have been successfully fabricated using PCDTBT : PC71BM with different mixing ratios (1 : 1 to 1 : 8) and the influence of hole transport layer thickness (PEDOT : PSS). The active layers with different mixing ratios of PCDTBT : PC71BM have been fabricated using o-dichlorobenzene (o-DCB). The surface morphology of the active layers and PEDOT : PSS layer with different thicknesses were characterized by AFM analysis. Here, we report that the OTFSCs with high performance have been optimized with 1 : 4 ratios of PCDTBT : PC71BM. The power conversion efficiency (PCE = 5.17%) of the solar cells was significantly improved by changing thickness of PEDOT : PSS layer. The thickness of the PEDOT : PSS layer was found to be of significant importance; the thickness of the PEDOT : PSS layer at 45 nm (higher spin speed 5000 rpm) shows higher short circuit current density (Jsc) and lower series resistance (Rs) and higher PCE.

High efficiency all phosphorescent white light-emitting diodes based on conjugated polymer host

High efficiency all phosphorescent white electroluminescence was realized by double doping of blue-light-emitting bis(2-(4,6-difluorophenyl)-pyridinato-N,C2′) picolinate (FIrpic) and red iridium complex Ir(DMFPQ)2pbm into conjugated polymer host poly(9,9-dioctylfluorene) (PFO). Effects of hole-transport layer (HTL) on the performances of white polymer light-emitting diodes (WPLEDs) were investigated. First of all, PVK as the HTL was essential, because the back energy transfer from FIrpic to PFO caused by the low-lying triplet energy level of PFO was suppressed by PVK. Furthermore, performances of the WPLEDs were enhanced by introducing CBP into PVK owing to improved balance of electron and hole current. The resulting all phosphorescent WPLEDs have a peak luminous efficiency of 15.5cd/A and a peak power efficiency of 6lm/W. Commisssion Internationale de L’Eclairage (CIE) coordinates of (0.41, 0.38) were realized at a current density of 18mA/cm2. The obtaining of the efficient all phosphorescent white electroluminescence with PFO as host polymer will broaden the approaches of white light generation and be a big promote for the application of phosphorescent WPLEDs.

Dramatic effects of hole transport layer on the efficiency of iridium-based organic light-emitting diodes

Electroluminescent efficiency of organic light-emitting diodes with Ir-based emitter depends strongly on the nature of the hole transport layer used. The efficiency is not correlated with the oxidation potential of the hole transport material. Instead, we found that many of the hole transport materials used can quench the photoluminescence intensity of the Ir green emitter and the photoluminescent quenching efficiency correlates well with the device efficiency. Based on the pulse radiolysis energy transfer experiments, we established the origin of the photoluminescent quenching as due to energy transfer from the excited state of Ir green emitter to the triplet state of the hole transport material.