Abstract Interfacial layer is deemed as an efficient approach to align the energy level and reduc... more Abstract Interfacial layer is deemed as an efficient approach to align the energy level and reduce the carrier recombination at the interfaces. Therefore, for the first time, a facile yet effective method to enhance carrier transport by copper oxide quantum dots (CuOx QDs) interfacial layer in inverted perovskite solar cells (PSCs) is developed. The high mobility of CuOx QDs interfacial layer could boost the performance of PSCs by providing a better electrical carrier transport. Furthermore, the higher crystallinity of perovskite layer on CuOx QDs layer reduced the charge trap state densities, which leads to an increase in carrier recombination resistance. As a result, our inverted PSCs exhibit a power conversion efficiency (PCE) of 19.91%, a 14.6% increment compared with the PCE of a control device. Our finding demonstrates the promise of enhancing carrier transport by interfacial layer for high-performance PSCs and expands choice of interfacial layer materials in PSCs.
physica status solidi (RRL) – Rapid Research Letters, 2019
Organic-inorganic lead halide perovskites have emerged rapidly as the most attractive materials f... more Organic-inorganic lead halide perovskites have emerged rapidly as the most attractive materials for photovoltaics in the last ten years. Intense research has been done on crystal growth and morphology control to improve their power conversion efficiencies. Furthermore, perovskites also show great potential for optical amplification and lasing. Despite the large amount of reports on how processing conditions affect the perovskite light harvesting properties, effects on amplified spontaneous emission (ASE) or lasing performance have attracted considerably less attention. In this work, a detailed study on the ASE performance of methylammonium lead triiodide (MAPbI 3) films processed with lead acetate (Pb(Ac) 2) as lead source following a one-step spin coating method and exposed to different post-deposition conditions is presented. It is found that the use of Pb(Ac) 2 instead of lead iodide (PbI 2) accelerates the crystal growth and simplifies the fabrication procedure. Even very thin MAPbI 3 films (~70 nm) can sufficiently support optical amplification and lasing in surface emitting distributed-feedback (DFB) cavities. The facile and highly controllable MAPbI 3 film
Uniform and dense perovskite films were realized by the one-step solution-processing method combi... more Uniform and dense perovskite films were realized by the one-step solution-processing method combined with toluene washing. The influence of the delay time applied for toluene washing on the film quality of CH 3 NH 3 PbI 3 (MAPbI 3) was investigated in a comprehensive manner. The optimal delay time was experimentally observed at the critical point when the color of the film changes from transparent to hazy. A detailed Xray diffraction study suggested that such a color change was caused by the emergence of the MAPbI 3 crystal nucleus. This finding provides a convenient method to determine the optimal time accurately. With the optimal delay time, the most uniformly distributed MAPbI 3 grains with the largest average grain size and the smoothest surface were obtained. Owing to the realization of homogeneous MAPbI 3 films combined with full coverage of perovskite on the substrate achieved by toluene washing at the critical point, open-circuit voltage, short-circuit current, fill factor, and power conversion efficiency of 1.11 V, 18.24 mA/cm 2 , 77.47, and 15.54% were obtained.
An important step of the great achievement of organic solar cells in power conversion efficiency ... more An important step of the great achievement of organic solar cells in power conversion efficiency is the development of lowband gap polymer donors, PBDBÀ T derivatives, which present interesting aggregation effects dominating the device performance. The aggregation of polymers can be manipulated by a series of variables from a materials design and processing conditions perspective; however, optimization of film quality is a time-and energy-consuming work. Here, we introduce a robot-based high-throughput platform (HTP) that is offering automated film preparation and optical spectroscopy thin-film characterization in combination with an analysis algorithm. PM6 films are prepared by the so-called spontaneous film spreading (SFS) process, where a polymer solution is coated on a water surface. Automated acquisition of UV/Vis and photoluminescence (PL) spectra and automated extraction of morphological features is coupled to Gaussian Process Regression to exploit available experimental evidence for morphology optimization but also for hypothesis formulation and testing with respect to the underlying physical principles. The integrated spectral modeling workflow yields quantitative microstructure information by distinguishing amorphous from ordered phases and assesses the extension of amorphous versus the ordered domains. This research provides an easy to use methodology to analyze the exciton coherence length in conjugated semiconductors and will allow to optimize exciton splitting in thin film organic semiconductor layers as a function of processing.
The morphology of perovskite light-absorption layer plays an important role in the performance of... more The morphology of perovskite light-absorption layer plays an important role in the performance of perovskite solar cells (PSCs). In this work, BiFeO3 (BFO) nanostructures were used as additive for CH3NH3PbI3 (MAPbI3) via anti-solvent method. The addition of BFO nanostructures greatly enhanced the crystallinity, grain size and film uniformity of MAPbI3. As a result, the charge carrier mobility and electron diffusion length increased, leading to the increase of the short circuit current (JSC) of PSCs. This work provides a very simple but effective approach to improve the morphology of perovskite layer for efficient PSCs.
Organometallic halide perovskite films based on lead iodide precursor often suffered from bad rep... more Organometallic halide perovskite films based on lead iodide precursor often suffered from bad repeatability and the usage of large quantities of toxic solvents due to the need for an anti-solvent washing process. Lead acetate (Pb(Ac) 2) precursor, by contrast, was more promising because of the needless of anti-solvent washing during the fabrication of perovskite films. However, the performance of perovskite solar cells (PSCs) needs to be improved. Here, we developed a simple strategy to improve the efficiency of PSCs by adding a small amount of dimethylsulfoxide (DMSO) into the precursor solution of perovskite. An increase in power conversion efficiency (PCE) of PSCs from 13.34% to 15.74% was achieved. It was found that with the addition of DMSO, a stable mesophase structure was formed, which significantly delayed the crystallization of perovskite during the spincoating of precursor solution, resulting in more uniform and dense perovskite films. The trap intensity and charge carrier mobility of the perovskite films were estimated. The charge carrier dynamic and the recombination in the PSCs were studied. Our method provided a convenient way to improve the performance of PSCs based on Pb(Ac) 2 precursor.
The commonly used electron transport material (6,6)-phenyl-C61 butyric acid methyl ester (PCBM) f... more The commonly used electron transport material (6,6)-phenyl-C61 butyric acid methyl ester (PCBM) for perovskite solar cells (PSC) with inverted planar structures suffers from properties such as poor film-forming. In this manuscript, we demonstrate a simple method to improve the film-forming properties of PCBM by doping PCBM with poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) as the electron transport layer (ETL), which effectively enhances the performance of CH3NH3PbI3 based solar cells. With 5 wt % F8BT in PCBM, the short circuit current (JSC) and fill factor (FF) of PSC both significantly increased from 17.21 ± 0.15 mA·cm−2 and 71.1 ± 0.07% to 19.28 ± 0.22 mA·cm−2 and 74.7 ± 0.21%, respectively, which led to a power conversion efficiency (PCE) improvement from 12.6 ± 0.24% to 15 ± 0.26%. The morphology investigation suggested that doping with F8BT facilitated the formation of a smooth and uniform ETL, which was favorable for the separation of electron-hole pairs, and therefor...
The non-radiative recombination, the main energy loss channel for open circuit voltage (V oc), is... more The non-radiative recombination, the main energy loss channel for open circuit voltage (V oc), is one of the crucial problems for achieving high power conversion efficiency (PCE) in inverted perovskite solar cells (PSCs). Usually, grain boundary passivation is considered as an effective way to reduce non-radiative recombination because the defects (uncoordinated ions) on grain boundaries are passivated. We added the hydroxyl and carbonyl functional groups contained carbon quantum dots (CQDs) into perovskite precursor solution to passivate the uncoordinated lead ions on grain boundaries. Higher photoluminescence intensity and longer carrier lifetime were demonstrated in the perovskite film with CQDs additive. This confirmed that the addition of CQDs can reduce non-radiative recombination by grain boundary passivation. Additionally, the introduction of CQDs could increase the thickness of perovskite film. Consequently, we achieved a champion device with PCE of 18.24%. The device with CQDs remained 73.4% of its initial PCE after aged for 48 hours under 80% humidity in the dark at room temperature. Our findings reveal the mechanisms of how CQDs passivate the grain boundaries of perovskite which can improve the efficiency and stability of perovskite solar cells.
Abstract Interfacial layer is deemed as an efficient approach to align the energy level and reduc... more Abstract Interfacial layer is deemed as an efficient approach to align the energy level and reduce the carrier recombination at the interfaces. Therefore, for the first time, a facile yet effective method to enhance carrier transport by copper oxide quantum dots (CuOx QDs) interfacial layer in inverted perovskite solar cells (PSCs) is developed. The high mobility of CuOx QDs interfacial layer could boost the performance of PSCs by providing a better electrical carrier transport. Furthermore, the higher crystallinity of perovskite layer on CuOx QDs layer reduced the charge trap state densities, which leads to an increase in carrier recombination resistance. As a result, our inverted PSCs exhibit a power conversion efficiency (PCE) of 19.91%, a 14.6% increment compared with the PCE of a control device. Our finding demonstrates the promise of enhancing carrier transport by interfacial layer for high-performance PSCs and expands choice of interfacial layer materials in PSCs.
physica status solidi (RRL) – Rapid Research Letters, 2019
Organic-inorganic lead halide perovskites have emerged rapidly as the most attractive materials f... more Organic-inorganic lead halide perovskites have emerged rapidly as the most attractive materials for photovoltaics in the last ten years. Intense research has been done on crystal growth and morphology control to improve their power conversion efficiencies. Furthermore, perovskites also show great potential for optical amplification and lasing. Despite the large amount of reports on how processing conditions affect the perovskite light harvesting properties, effects on amplified spontaneous emission (ASE) or lasing performance have attracted considerably less attention. In this work, a detailed study on the ASE performance of methylammonium lead triiodide (MAPbI 3) films processed with lead acetate (Pb(Ac) 2) as lead source following a one-step spin coating method and exposed to different post-deposition conditions is presented. It is found that the use of Pb(Ac) 2 instead of lead iodide (PbI 2) accelerates the crystal growth and simplifies the fabrication procedure. Even very thin MAPbI 3 films (~70 nm) can sufficiently support optical amplification and lasing in surface emitting distributed-feedback (DFB) cavities. The facile and highly controllable MAPbI 3 film
Uniform and dense perovskite films were realized by the one-step solution-processing method combi... more Uniform and dense perovskite films were realized by the one-step solution-processing method combined with toluene washing. The influence of the delay time applied for toluene washing on the film quality of CH 3 NH 3 PbI 3 (MAPbI 3) was investigated in a comprehensive manner. The optimal delay time was experimentally observed at the critical point when the color of the film changes from transparent to hazy. A detailed Xray diffraction study suggested that such a color change was caused by the emergence of the MAPbI 3 crystal nucleus. This finding provides a convenient method to determine the optimal time accurately. With the optimal delay time, the most uniformly distributed MAPbI 3 grains with the largest average grain size and the smoothest surface were obtained. Owing to the realization of homogeneous MAPbI 3 films combined with full coverage of perovskite on the substrate achieved by toluene washing at the critical point, open-circuit voltage, short-circuit current, fill factor, and power conversion efficiency of 1.11 V, 18.24 mA/cm 2 , 77.47, and 15.54% were obtained.
An important step of the great achievement of organic solar cells in power conversion efficiency ... more An important step of the great achievement of organic solar cells in power conversion efficiency is the development of lowband gap polymer donors, PBDBÀ T derivatives, which present interesting aggregation effects dominating the device performance. The aggregation of polymers can be manipulated by a series of variables from a materials design and processing conditions perspective; however, optimization of film quality is a time-and energy-consuming work. Here, we introduce a robot-based high-throughput platform (HTP) that is offering automated film preparation and optical spectroscopy thin-film characterization in combination with an analysis algorithm. PM6 films are prepared by the so-called spontaneous film spreading (SFS) process, where a polymer solution is coated on a water surface. Automated acquisition of UV/Vis and photoluminescence (PL) spectra and automated extraction of morphological features is coupled to Gaussian Process Regression to exploit available experimental evidence for morphology optimization but also for hypothesis formulation and testing with respect to the underlying physical principles. The integrated spectral modeling workflow yields quantitative microstructure information by distinguishing amorphous from ordered phases and assesses the extension of amorphous versus the ordered domains. This research provides an easy to use methodology to analyze the exciton coherence length in conjugated semiconductors and will allow to optimize exciton splitting in thin film organic semiconductor layers as a function of processing.
The morphology of perovskite light-absorption layer plays an important role in the performance of... more The morphology of perovskite light-absorption layer plays an important role in the performance of perovskite solar cells (PSCs). In this work, BiFeO3 (BFO) nanostructures were used as additive for CH3NH3PbI3 (MAPbI3) via anti-solvent method. The addition of BFO nanostructures greatly enhanced the crystallinity, grain size and film uniformity of MAPbI3. As a result, the charge carrier mobility and electron diffusion length increased, leading to the increase of the short circuit current (JSC) of PSCs. This work provides a very simple but effective approach to improve the morphology of perovskite layer for efficient PSCs.
Organometallic halide perovskite films based on lead iodide precursor often suffered from bad rep... more Organometallic halide perovskite films based on lead iodide precursor often suffered from bad repeatability and the usage of large quantities of toxic solvents due to the need for an anti-solvent washing process. Lead acetate (Pb(Ac) 2) precursor, by contrast, was more promising because of the needless of anti-solvent washing during the fabrication of perovskite films. However, the performance of perovskite solar cells (PSCs) needs to be improved. Here, we developed a simple strategy to improve the efficiency of PSCs by adding a small amount of dimethylsulfoxide (DMSO) into the precursor solution of perovskite. An increase in power conversion efficiency (PCE) of PSCs from 13.34% to 15.74% was achieved. It was found that with the addition of DMSO, a stable mesophase structure was formed, which significantly delayed the crystallization of perovskite during the spincoating of precursor solution, resulting in more uniform and dense perovskite films. The trap intensity and charge carrier mobility of the perovskite films were estimated. The charge carrier dynamic and the recombination in the PSCs were studied. Our method provided a convenient way to improve the performance of PSCs based on Pb(Ac) 2 precursor.
The commonly used electron transport material (6,6)-phenyl-C61 butyric acid methyl ester (PCBM) f... more The commonly used electron transport material (6,6)-phenyl-C61 butyric acid methyl ester (PCBM) for perovskite solar cells (PSC) with inverted planar structures suffers from properties such as poor film-forming. In this manuscript, we demonstrate a simple method to improve the film-forming properties of PCBM by doping PCBM with poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) as the electron transport layer (ETL), which effectively enhances the performance of CH3NH3PbI3 based solar cells. With 5 wt % F8BT in PCBM, the short circuit current (JSC) and fill factor (FF) of PSC both significantly increased from 17.21 ± 0.15 mA·cm−2 and 71.1 ± 0.07% to 19.28 ± 0.22 mA·cm−2 and 74.7 ± 0.21%, respectively, which led to a power conversion efficiency (PCE) improvement from 12.6 ± 0.24% to 15 ± 0.26%. The morphology investigation suggested that doping with F8BT facilitated the formation of a smooth and uniform ETL, which was favorable for the separation of electron-hole pairs, and therefor...
The non-radiative recombination, the main energy loss channel for open circuit voltage (V oc), is... more The non-radiative recombination, the main energy loss channel for open circuit voltage (V oc), is one of the crucial problems for achieving high power conversion efficiency (PCE) in inverted perovskite solar cells (PSCs). Usually, grain boundary passivation is considered as an effective way to reduce non-radiative recombination because the defects (uncoordinated ions) on grain boundaries are passivated. We added the hydroxyl and carbonyl functional groups contained carbon quantum dots (CQDs) into perovskite precursor solution to passivate the uncoordinated lead ions on grain boundaries. Higher photoluminescence intensity and longer carrier lifetime were demonstrated in the perovskite film with CQDs additive. This confirmed that the addition of CQDs can reduce non-radiative recombination by grain boundary passivation. Additionally, the introduction of CQDs could increase the thickness of perovskite film. Consequently, we achieved a champion device with PCE of 18.24%. The device with CQDs remained 73.4% of its initial PCE after aged for 48 hours under 80% humidity in the dark at room temperature. Our findings reveal the mechanisms of how CQDs passivate the grain boundaries of perovskite which can improve the efficiency and stability of perovskite solar cells.
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