Power Conversion Efficiency Of Perovskite Solar Cells Research Articles

Recent Advances in g-C3N4 for the Application of Perovskite Solar Cells.

In this study, graphitic carbon nitride (g-C3N4) was extensively utilized as an electron transport layer or interfacial buffer layer for simultaneously realizing photoelectric performance and stability improvement of perovskite solar cells (PSCs). This review covers the different g-C3N4 nanostructures used as additive and surface modifier layers applied to PSCs. In addition, the mechanism of reducing the defect state in PSCs, including improving the crystalline quality of perovskite, passivating the grain boundaries, and tuning the energy level alignment, were also highlighted in this review. Currently, the power conversion efficiency of PSCs based on modified g-C3N4 has been increased up to 22.13%, and its unique two-dimensional (2D) package structure has enhanced the stability of PSCs, which can remain stable in the dark for over 1500 h. Finally, the potential challenges and perspectives of g-C3N4 incorporated into perovskite-based optoelectronic devices are also included in this review.

Efficient Perovskite Solar Cells via Phenethylamine Iodide Cation-Modified Hole Transport Layer/Perovskite Interface.

Perovskite solar cells (PeSCs) were fabricated by using CsxFA1–xPbI3–xClx as the photoactive layer, and the effects of different proportions of cesium chloride (CsCl)/formamidinium iodide on perovskites were investigated. Cesium (Cs) can stabilize the α phase of the perovskite, while chlorine (Cl) can increase the size and crystallinity of perovskite crystals and reduce non-radiative cladding, thereby improving the performance of the overall device. The maximum power conversion efficiency (PCE) measured for Cs0.2FA0.8PbI2.8Cl0.2-based PeSCs was 18.9%. To further improve the photovoltaic characteristics of PeSCs, Cs0.2FA0.8PbI2.8Cl0.2-based PeSCs were introduced into different concentrations of phenethylammonium iodide (PEAI) to modify the interface between the NiOx hole transport layer (HTL) and the perovskite photoactive layer, which can simultaneously promote excellent crystallinity of the perovskite layer and passivated interfacial defects, reducing recombination near the perovskite/HTL interface in PeSCs, thereby increasing the efficiency of the device. Compared with the control Cs0.2FA0.8PbI2.8Cl0.2-based PeSC, the PCE of PeSC with the PEAI (10 mg/mL)-modified NiOx/perovskite interface increased significantly from 18.9 to 20.2%.

Spiro-OMeTAD-Based Hole Transport Layer Engineering toward Stable Perovskite Solar Cells.

Perovskite solar cells (PSCs) have undergone unprecedented growth in the past decade as an emerging photovoltaic technology. Up till now, the power conversion efficiency of PSCs has exceeded 25% that rivals silicon solar cells and there is still room for further enhancement. However, the development in long-term stability lags far behind, which remains a great concern for the commercial application in the future. The device instability mainly arises from the functional components, including perovskite film, charge transport layers, and electrodes along with the involved interfaces. As the most widely studied hole transport layer at the current stage, 2,2',7,7'-tetrakis(N,N-di(4-methoxyphenyl)amino)-9,9-spirobifluorene (Spiro-OMeTAD) helps contribute to the achievement of record efficiency but it weakens the device stability due to the doping-induced side effects such as hygroscopicity and ion migration. Great efforts are devoted to boosting the stability of Spiro-OMeTAD while maintaining excellent photovoltaic performance. In this review, the fundamental properties of Spiro-OMeTAD have been summarized and the recent advances in engineering Spiro-OMeTAD-based hole transport layer for the sake of highly efficient PSCs with enhanced longevity are highlighted. In the end, an outlook for the further optimization of Spiro-OMeTAD is provided and the issues related to large-scale production are discussed.

Amorphous TiO2 film with fiber like structure: An ideal candidate for ETL of perovskite solar cells

• E T L A m o r p h o u s T i O 2 was prepared by DCP-MS at room temperature. • Lots fiber like structures run through the E T L A m o r p h o u s T i O 2 directly. • Fiber like structures in E T L A m o r p h o u s T i O 2 improves electron transfer efficiency. • PCE of PSCs improves from 4.7% of E T L A n a t a s e T i O 2 to 11.5% of E T L A m o r p h o u s T i O 2 . Organic-inorganic hybrid metal halide perovskite solar cells (PSCs) with planar heterojunction structures were fabricated. The amorphous and anatase TiO 2 electron transfer layer (ETL) was deposited by the direct current pulsed magnetron sputtering technology. With the ordinary CH 3 NH 3 PbI 3 , PSCs with amorphous and anatase TiO 2 ETL showed the average power conversion efficiency in (11.5 ± 0.7)% and (4.7 ± 1.5)%, respectively. Combining with XRD and TEM results, the fiber like structure in amorphous TiO 2 ETL resulted in the increase of average power conversion efficiency of PSCs. Finally, amorphous TiO 2 with fiber like structure is an ideal ETL for PSCs, which is prepared by sputtering.

Perovskite-Surface-Confined Grain Growth for High-Performance Perovskite Solar Cells.

The conventional post-annealing (CPA) process is frequently employed and regarded a crucial step for high-quality perovskite thin-films. However, most researchers end up with unwanted characteristics because controlling the evaporation rate of perovskite precursor solvents during heat treatment is difficult. Most perovskite thin-films result in rough surfaces with pinholes and small grains with multiple boundaries, if the evaporation of precursor solvents is not controlled in a timely manner, which negatively affects the performance of perovskite solar cells (PSCs). Here, we present a surface-confined post-annealing (SCPA) approach for controlling the evaporation of perovskite precursor solvents and promoting crystallinity, homogeneity, and surface morphology of the resulting perovskites. The SCPA method not only modulates the evaporation of residual solvents, resulting in pinhole-free thin-films with large grains and fewer grain boundaries, but it also reduces recombination sites and facilitates the transport of charges in the resulting perovskite thin-films. When the method is changed from CPA to SCPA, the power conversion efficiency of PSC improves from 18.94% to 21.59%. Furthermore, as compared to their CPA-based counterparts, SCPA-based PSCs have less hysteresis and increased long-term stability. The SCPA is a potentially universal method for improving the performance and stability of PSCs by modulating the quality of perovskite thin-films.

Modulating preferred crystal orientation for efficient and stable perovskite solar cells—From progress to perspectives

AbstractThe perovskite solar cell (PSC) has been recognized as a promising candidate for the next generation of photovoltaics due to its excellent power conversion efficiency (PCE), potential low cost and straightforward solution preparation processes. With efforts around the world, the PCE of PSCs has reached 25.7%. As the perovskite film is the most important part of a PSC, its quality dramatically affects the efficiency and stability of the PSC. Numerous works have focused on controlling crystallization to realize oriented growth of perovskite films. Particularly, considering the photoelectric anisotropy of perovskite materials, it is very meaningful to investigate the relationship between preferred crystal orientation and device efficiency and stability. This review highlights various approaches for realizing preferred crystal orientation of polycrystalline perovskite films, including optimizing the perovskite precursor solution and film annealing process, additive engineering, and interface engineering. Furthermore, the key factors affecting oriented crystal growth are carefully discussed, which provides effective guidance to obtain highly‐oriented perovskite films for highly efficient and stable PSCs.image

Near‐Band‐Edge Enhancement in Perovskite Solar Cells via Tunable Surface Plasmons

AbstractPlasmonic perovskite solar cells (PSCs) using core−shell type plasmonic particles are designed, which possess the plasmon resonance in the near‐infrared range. This can selectively strengthen the interaction of the perovskite layer with low‐energy photons. The mesoporous PSCs employing the plasmonic particles have delivered a 10%–15% enhancement of external quantum efficiency in the plasmonic resonance range. This surface‐plasmonic effect has been analyzed using complementary techniques, including selective wavelength excitation and time‐dependent photoluminescence. It is shown that the metal‐based core−shell‐type plasmonic structures in PSCs optimize the scattering and absorption of incident light and the dynamics of photogenerated carriers. Furthermore, both optical and electronic effects increase the power conversion efficiency of PSCs from 17.49% to 19.88%, paving a way toward controlling the thickness of the photoactive layer for advanced devices such as tandem solar cells.

Carrier Management via Integrating InP Quantum Dots into Electron Transport Layer for Efficient Perovskite Solar Cells

Metal oxides are the most efficient electron transport layers (ETLs) in perovskite solar cells (PSCs). However, issues related to the bulk (i.e., insufficient electron mobility, unfavorable energy level position) and interface of metal oxide/perovskite (detrimental surface hydroxyl groups) limit the transport kinetics of photoinduced electrons and prevent PSCs from unleashing their theoretical efficiency potential. Herein, the inorganic InP colloid quantum dots (CQDs) with outstanding electron mobility (4600 cm2 V-1 s-1) and carboxyl (-COOH) terminal ligands were uniformly distributed into the metal oxide ETL to form consecutive electron transport channels. The hybrid InP CQD-based ETL demonstrates a more N-type characteristic with more than 3-fold improvement in electron mobility. The formation of the Sn-O-In bond facilitates electron extraction due to suitable energy level alignment between the ETL and perovskite. The strong interaction between uncoordinated Pb2+ at the perovskite/ETL interface and the -COO- in the ligand of InP CQDs reduces the density of defects in perovskite. As a result, the hybrid InP CQD-based ETL with an optimized InP ratio (18 wt %) boosts the power conversion efficiency of PSCs from 22.38 to 24.09% (certified efficiency of 23.43%). Meanwhile, the device demonstrates significantly improved photostability and atmospheric storage stability.

Determining the dependence of solar cell power conversion efficiency on fabrication parameters in inorganic perovskite types by programming gene expression

This article is an attempt to review inorganic perovskite solar cells and propose a new predictive model to estimate the power conversion efficiency (PCE) using gene expression programming (GEP). All references used the spin coating method to construct the solar cells. For the perovskite layer, parameters of thickness, bandgap, and mass percentage of repetitive elements of perovskite layers were considered as input variables, and the PCE was selected as the output variable. In the first stage, 29 experiments were extracted from reliable articles. As a first step to ensure the robustness of the selected data, the box plot was used to determine the distribution of operational parameters, and the outlier's data (three data sets) were excluded. Remained data set used to construct models by training (19 data sets) and testing (7 data sets) in GEP. Statistical indices including the absolute fraction of variance (R 2 ), root mean square error (RMSE), root relative squared error (RRSE), mean squared error (MSE), and box plot of variables were used to evaluate the accuracy of the proposed models. Finally, the best model was selected by R 2 = 0.9111, RMSE = 0.0878, RRSE = 0.2995, and MSE = 0.0077. The results showed that GEP can be used as a unique tool for modeling PCE in perovskite solar cells with operational parameters. Sorting out the effect of each parameter on PCA was the next strength of this study, which was performed using sensitivity analysis and showed that bandgap, the mass percentage of cesium (Cs), lead (Pb) and iodine (I) were the most influencing parameters on the PCE from the inorganic perovskite solar cells, respectively. • The perovskite layer on PCE plays an important role in understanding the behavior of these solar cells. • Review inorganic perovskite solar cells and propose a new predictive model to estimate the PCE using GEP. • GEP can be used as a unique tool for modeling PCE in perovskite solar cells with operational parameters. • Sorting out the effect of each parameter on PCE was strength of this study, which was performed using sensitivity analysis. • Bandgap, mass percentage of Cs, Pb and I were the most influencing parameters on PCE from the inorganic perovskite solar cells.

Ni-Doped SnO2 as an Electron Transport Layer by a Low-Temperature Process in Planar Perovskite Solar Cells.

Perovskite solar cells (PSCs) based on a planar structure have recently become more attractive due to their simple manufacturing process and relatively low cost, while most perovskite solar cells employ highly porous TiO2 as an electron transport layer in mesoporous devices offering higher energy conversion efficiency (PCE). In planar structural devices, non-radiative recombination effects of the absorber layer and the electron transport layer cause potential loss and lower PCE. We created an efficient electron transport layer by combining low-temperature Ni-doped SnO2 with SDBS as a surfactant (denoted as Ni:SnO2). Doping Ni+ into low-temperature solution-processed SnO2 increased the power conversion efficiency of PSCs from 17.8 to 19.7%.

An energy level alignment strategy to boost the open-circuit voltage via a Mg:TiO2 compact layer in the planar heterojunction CsPbBr3 solar cells

The suitable energy level alignment between the electron transport layer (ETL) and perovskite absorber for facilitating electron extraction and transfer is essential for planar heterojunction perovskite solar cells (PSCs) to achieve high power conversion efficiency (PCE). The planar heterojunction CsPbBr3 PSCs have attracted increasing attention due to their high stability in ambient in which TiO2 is often used as the ETL. Actually, there is a large energy barrier between the conduction bands of TiO2 and CsPbBr3, which limits the open-circuit voltage (VOC) and PCE of PSCs. Herein, we effectively optimized the energy level alignment between CsPbBr3 and TiO2 by tuning the Mg incorporation level in the latter. The Fermi level of TiO2 ETL was gradually shifted upward using Mg incorporation, which led to a favorable band bending between TiO2 and CsPbBr3 and reduced the interfacial band offset. Consequently, the VOC of the devices was effectively increased from 1.36 to 1.49 V, and the corresponding PCE was also increased from 6.87% to 8.76%. This work highlights the importance of the energy level alignment between ETLs and perovskite absorbers for high-performance devices and offers an effective means to address the large energy barrier between the conduction bands of TiO2 and CsPbBr3.

Hydrophobic Graphene Quantum Dots for Defect Passivation and Enhanced Moisture Stability of CH3NH3PbI3 Perovskite Solar Cells

Passivating the defects and grain boundaries (GBs) of perovskite films at the interface by interface engineering is a promising route to achieve efficient and stable perovskite solar cells (PSCs). Herein, a new type of graphene, that is, hydrophobic graphene quantum dots (HGQDs) containing amide linkages, which consist of carbonyl and dodecyl amine groups, is successfully used as a bifunctional interface modifier to engineer the interface of the perovskite/hole transport layer. A comprehensive characterization including X‐ray photoelectron spectroscopy, Fourier‐transform photocurrent spectroscopy, Raman spectroscopy, photoluminescence spectroscopy, and space‐charge‐limited current measurements is performed to identify the underlying passivation mechanisms. It can be demonstrated that the HGQDs, due to the bifunctional groups containing N and O atoms, effectively passivate the uncoordinated Pb2+ ions at the perovskite film surface and GBs and consequently induce a lower trap state density. Moreover, HGQDs enhance the quality of the perovskite film which reduces the charge recombination at the interface. Therefore, the power conversion efficiency of PSCs treated with HGQDs is significantly increased from 16.00% to 18.30%, mainly based on the improved open‐circuit voltage and fill factor. Importantly, the HGQDs featuring hydrophobicity due to alkyl chains significantly enhance moisture stability.

Incorporating polyvinyl pyrrolidone in green anti-solvent isopropanol: A facile approach to obtain high efficient and stable perovskite solar cells

Polymer additive is an effective candidate for passivating perovskite layers, which can lead to high efficiency and stability for perovskite solar cells (PSCs). Herein, we introduce a nontoxic, environment-friendly poly (4-vinylpyridine) (PVP) additives, which is beneficial in optimizing perovskite films, into the green anti-solvent isopropanol. Analysis of the photoluminescence imaging and transient spectroscopic measurements confirm the reduction in nonradiative recombination in the passivated device. The Fourier transform infrared spectroscopy and Hydrogen nuclear magnetic spectra indicate that PVP can efficiently passivate the perovskites via sharing the lone pair electrons of carbon-oxygen double bond (C=O) with uncoordinated lead ions. Furthermore, an extra hydrogen bond between PVP and CH3NH3+ (Methylammonium, MA+) can be observed by the Hydrogen Magnetic Resonance Spectroscopy. The C-O band locks MA+ through hydrogen bond which suppresses ion migration and further stabilizes the perovskite crystal structure. As a result, the power conversion efficiency of PSC increases from 15.2% to 18.2%. This work provides an environment-friendly method to introduce polymers into the fabrication of highly efficient and stable PSCs.

Energy level matching between transparent conducting electrodes and the electronic transport layer to enhance performance of all-inorganic CsPbBr3 solar cells

Perovskite solar cells (PSCs) have become a promising research direction in photovoltaic field, where the evolution of the transparent conductive oxides (TCOs) electrodes, a vital part of photovoltaic devices, has played a distinctive role in their development. To date, the indium tin oxide (ITO) and fluorine-doped tin oxide (FTO) have been widely used as TCOs in state-of-the-art PSCs. However, the energy level matching between the TCO electrodes and the electron transport layers (ETLs) are usually ignored. Herein, Ta doped SnO2 (TTO) films have been prepared by the high target utilisation sputtering (HiTUS) technology, which exhibited the lowest resistivity of 7.8 × 10−4 Ω cm and the average transmittance in the visible light region over 85%. A maximum power conversion efficiency (PCE) with 6.48% was achieved when the TTO films as the bottom electrodes in CsPbBr3 PSCs, higher than that of PSCs based on FTO (5.36%). Especially, the open-circuit voltage (Voc), short-circuit current (Jsc) and fill factor (FF) were all enhanced, which were attributed to the suitable energy level matching between the TCOs and ETLs layers and their low interface roughness. This work demonstrates the band structure of the TCOs and ETL layers and the roughness of TCOs have more important influence on the PCE of PSCs under the similar optical and electrical properties of TCOs condition.

Yttrium‐doped Sn3O4 two‐dimensional electron transport material for perovskite solar cells with efficiency over 23%

AbstractThe two‐dimensional mixed‐valence tin oxide Sn3O4 with a low defect density of states and suitable energy band structure has shown great potential as the electron transport layer (ETL) for perovskite solar cells (PSCs). However, the electron density of Sn3O4 is low and should be modulated to demonstrate its application for more efficient PSCs. Here, Sn3O4 is doped with yttrium (Y) to optimize its electronic properties and improve the performance of PSCs based on Sn3O4 ETL. The conductivity of Sn3O4 is improved from 6.6 × 10−4 to 2.05 × 10−3 S m−1 with increased electron density by Y doping. Meanwhile, the Fermi level of Sn3O4 is also upshifted after doping. The increased electron density and upshifted Fermi level enhance the electron extraction capability of Sn3O4 and built‐in potential in PSCs. By doping the Sn3O4 ETL with Y, the power conversion efficiency of PSCs is successfully boosted to 23.05%.image

Suppressing charge recombination in planar perovskite solar cells by using SnO2/TiO2 nanocomposite as electron transfer layer

Hybrid perovskite solar cells (PSCs) have been paid great attention owing to their excellent photovoltaic properties. However, the presence of charge recombination at the interface of the electron transport layer (ETL)/perovskite hinders the performance of perovskite solar cells, preventing them from reaching the Shockley–Queisser limit. Herein, the SnO2/TiO2 nanoparticles (NPs) composite (S/T-NC) ETL is developed by adopting a simple method at low temperature and applied into planar PSCs. Our results show that the maximum power conversion efficiency of PSCs based on the S/T-NC ETL is 20.51% with a VOC of 1.09 V, a JSC of 24.15 mA/cm2, and a fill factor of 77.84%, much higher than that for both SnO2 NPs based PSCs (18.19%) and TiO2 NPs based PSCs (17.81%). Further analysis reveals that the mixing of TiO2 and SnO2 can improve film quality and reduce trap density, thus, suppressing charge recombination and improving stability. These findings prove that the use of SnO2/TiO2 composite ETL is an effective way to further improve the performance for planar PSCs.

The impact of annealing process on the grain morphology and performance of mesoporous n-i-p carbon-based perovskite solar cells

Organic–inorganic perovskite solar cells (PSCs) have been emerging as one of the most promising photovoltaic technologies. Surface morphology is considered as a key-parameter in energy alignment and plays a dominant role in specifying the device performance. The large grains and low roughness enhance the transport of charge carriers from perovskite layers to the transport layers, and this reflects on the delivered power conversion efficiency (PCE). Therefore, in this study, we investigated the influence of the fabrication parameters on the grain size and the morphology of perovskite layers, thereby the PCE of PSCs. These parameters included the anti-solvent nature (chlorobenzene or toluene), annealing temperature, and annealing ramp rate (slow or flash annealing). The scanning electron microscope confirmed that flash annealing results in a better morphology than slow annealing whether by employing an anti-solvent dripping or not. Furthermore, the dripping of chlorobenzene as an anti-solvent produced better morphology and large grains compared with toluene. Therefore, combining chlorobenzene with flash annealing induced the formation of large grains, full cover, and a uniform perovskite layer, which reflects on the performance of the fabricated PSCs. Finally, employing the aforementioned optimum preparation parameters to fabricate carbon-based PSCs resulted in decent PCE, current density short circuit (Jsc), open circuit voltage (Voc), and fill factor (FF) of 7%, 11.3 mA/cm2, 0.74 V, and 34%, respectively.

Simple hybrid dithiafulvenes-triphenylamine systems as dopant-free hole-transporting materials for efficient perovskite solar cells

Two extended hybrid conjugated systems based on a triphenylamine (TPA) core with two and three peripheral 1,4-dithiafulvenes (DTF) units coded WH-2 and WH-3 as hole-transporting materials (HTMs) applied in perovskite solar cells (PSCs) are synthesized by facile one-step reaction in good yield over 75%. DTF unit as electron donor can enhance the electron donating ability and the fusion of benzenic ring of TPA with DTF unit may lead to reinforced intermolecular interactions in the solid state. In addition, WH-2 and WH-3 exhibit a pyramid shape containing partial planarity and quasi three-dimensionality features, which is also conducive to enhancing the π-π stacking of molecules in the solid state. The above-mentioned structural characteristics make the two HTMs have good hole mobilities. As a result, WH-2 and WH-3 obtained the high intrinsic hole mobilities of 4.69 × 10−4 and 2.18 × 10−3 cm2 V−1 s−1 respectively. Finally, the power conversion efficiencies (PCEs) of PSCs with WH-2 and WH-3 as cost-effective dopant-free HTMs are 15.39% and 19.22% respectively and the PCE of PSC with WH-3 is on a par with that of PSC with Li-TFSI/t-BP doped Spiro-OMeTAD (19.67%).

Phenethylamine‐Based Interfacial Dipole Engineering for High Voc Triple‐Cation Perovskite Solar Cells

AbstractSurface modification of 3D hybrid perovskites using 2D perovskites, such as phenethylamine halides (PEAX), increases the overall power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). The effect is based on a surface passivation phenomenon where PEAX is in direct contact with the perovskite and hole transport layer (HTL). However, it is herein observed that the PCE of PSCs containing PEAX increases significantly when they are not in direct contact with either the bottom layers (perovskites) or top layers (HTLs). Moreover, the highest PCE (>22%) is obtained for the PSCs when PEAX is not in contact with HTLs by using poly(methyl methacrylate) (PMMA). Photoemission measurements reveal that the shift of the highest occupied molecular orbital of the hole transporting material (a donor‐acceptor‐donor molecule synthesized for the study) to a deeper level results in an increased hole transfer at the perovskite/HTL interface leading to an improved device performance. It is proposed that PEAX acts as dipoles aligned between perovskite and HTL resulting in a shift in the energy levels. The combination of PEAX/PMMA at the interface enables high open‐circuit voltage (1.19V) close to the Shockley–Queisser limit for the triple‐cation (Cs‐MA‐FA) perovskites (bandgap, 1.51 eV).

Optimization of Lead Base Perovskite Solar Cell with ZnO and CuI as Electron Transport Material and Hole Transport Material Using SCAPS-1D

Perovskite solar cells (PSCs) research is substantially drawing attention because of the fast improvement in their power conversion efficiency (PCE), cheapness, possibility to tune the bandgap, low recombination rate, high open circuit voltage, excellent ambipolar charge carrier transport and strong and broad optical absorption. In this research, Zinc oxide as electron transport material (ETM) and copper iodide as hole transport material (HTM) have been optimized using SCAPS-1D simulation software. The thickness, bandgap, of ZnO (ETM) and CuI (HTM) was investigated. Results shows that the thickness and bandgap were found to strongly influence the PCE of perovskite solar cell. ZnO/CuI was found to be a better replacement to TiO2/Cu2O for stability and low degradation rate. It was observed that the maximum efficiency is 22.04%, Voc of 0.84V, JSC of 32.83mA/cm2 and FF of 79.79% was obtained when the thickness of ETM and HTM layer of (CH3NH3PbI3) PSCs which was found to be optimum at 0.2μm for the final optimization.