Publication date: March 2022
Source: Nano Energy, Volume 93
Author(s): Insik Yun, Yeonghee Lee, Young-Geun Park, Hunkyu Seo, Won Gi Chung, Soo-Jin Park, Jin-Woo Cho, Jun Hyeok Lee, Ravi Prakash Srivastava, Rira Kang, Byunghong Lee, Dahl-Young Khang, Sun-Kyung Kim, Jun Hong Noh, Jang-Ung Park
Publication date: March 2022
Source: Nano Energy, Volume 93
Author(s): Dae Hwan Lee, Do Hui Kim, Taehyun Kim, Dong Chan Lee, Shinuk Cho, Taiho Park
The synergistic optimization of 4-aminomethyltetrahydropyran and 1-chlorobutane successfully passivates cation and anion defects, effectively mitigates carrier nonradiative recombination, and achieves perovskite solar cells with high photovoltaic performance and a champion power conversion efficiency of 22.74%.
Perovskite layer, as the origin of optical–electrical conversion of devices, plays a very important role in perovskite solar cells (PSCs). However, lots of lead cations and halogen anions defects inevitably exit in the bulk and surface of the perovskite layer. These defects, serve as nonradiative recombination centers, degrade the performance, and damage the stability of PSCs. Herein, a strategy that anion and cation defects on the interface and in the bulk of perovskites are simultaneously passivated by doping organic molecule 4-aminomethyl tetrahydropyran (4-AMPR) and the surface modification with 1-chlorobutane (1-CB) in/on the perovskite is demonstrated. The O atoms on 4-AMPR can coordinate with the Pb vacancy and antisite Pb defects, as well as improve perovskite morphology. The volatilization of low-boiling 1-CB can passivate the halogen ion defects and promote the uniform nucleation of perovskite. The PSCs jointly optimized by 4-AMPR and 1-CB achieve a power conversion efficiency of 22.74% and retain 90.7% of the initial efficiency after storage in air environment (RH 10 ± 5%, 25 °C) for more than 1000 h. This research demonstrates a promising strategy for simultaneously mitigating anion and cation defects both in bulk and surface of perovskite layer and thus enhancing the performance and stability of the devices.
An N-substituted asymmetric nonfullerene acceptor SN with an over 40 nm bathochromically shifted absorption compared to Y6 is designed and synthesized. The PM6 : SN-based binary cell exhibits the lowest nonradiative voltage loss of 0.15 eV ever achieved by organic solar cells (OSCs). Benefiting from extended NIR absorption and lowered voltage loss, PM6 : Y6 : SN-based semitransparent (ST)-OSCs, for the first time, achieve a power conversion efficiency of 14 % with an average visible transmittance over 20 %.
Semitransparent organic solar cells (ST-OSCs) are considered as one of the most valuable applications of OSCs and a strong contender in the market. However, the optical band gap of current high-performance ST-OSCs is still not low enough to achieve the optimal balance between power conversion efficiency (PCE) and average visible transmittance (AVT). An N-substituted asymmetric nonfullerene acceptor SN with over 40 nm bathochromically shifted absorption compared to Y6 was designed and synthesized, based on which the device with PM6 as donor obtained a PCE of 14.3 %, accompanied with a nonradiative voltage loss as low as 0.15 eV. Meanwhile, ternary devices with the addition of SN into PM6 : Y6 can achieve a PCE of 17.5 % with an unchanged open-circuit voltage and improved short-circuit current. Benefiting from extended NIR absorption and lowered voltage loss, ST-OSCs based on PM6 : SN : Y6 were fabricated and the optimized device demonstrated a PCE of 14.0 % at an AVT of 20.2 %, which is the highest PCE at an AVT over 20 %.
An ionic liquid (IL) is designed to passivate undercoordinated Pb2+ by chemically bonding to form an IL capped perovskite surface, leading to superior photovoltaic performance and operational stability. Specifically, the small solar cell (0.1 cm2) exhibits an open-circuit voltage of 1.192 V, power conversion efficiency of 24.33%, and the large area (10.75 cm2) integrated module achieves a PCE of 20.33%.
Metal-halide perovskite has emerged as an effective photovoltaic material for its high power conversion efficiency (PCE), low cost and straightforward fabrication techniques. Unfortunately, its long-term operational durability, mainly affected by halide ion migration and undercoordinated Pb2+ is still the bottleneck for its large-scale commercialization. In this work, an ionic liquid (IL) is designed to effectively cap the grain surface for improved stability and reduced trap density. More specifically, the Br− in the IL passivates the undercoordinated Pb2+ by chemically bonding to it, resulting in a thin layer of ionic-liquid-perovskite formed on the surface, leading to improved photovoltaic performance and better stability. Specifically, the solar cell exhibits an open-circuit voltage of 1.192 V and PCE of 24.33% under one-sun illumination with negligible hysteresis, and a large area (10.75 cm2) integrated module achieves PCE of 20.33%. Moreover, the bare device maintains over 90% of its initial efficiency after 700 h of aging at 65 °C. It also shows outstanding stability with only about 10% degradation after being exposed to the ambient environment for 1000 h. The superior efficiency and stability demonstrate that the present IL passivating strategy is a promising approach for high-performance large area perovskite solar cell applications.
Single-crystal solar cells with high efficiency and a superior weak light response are achieved by engineering the hole extraction interface. Remarkably enhanced efficiency of 22.1% under AM 1.5G irradiation and indoor efficiency of 39.2% under 1000 lux irradiation are obtained, which are both the highest values for MAPbI3 single-crystal solar cells.
Perovskite single crystals have recently been regarded as emerging candidates for photovoltaic application due to their improved optoelectronic properties and stability compared to their polycrystalline counterparts. However, high interface and bulk trap density in micrometer-thick thin single crystals strengthen unfavorable nonradiative recombination, leading to large open-circuit voltage (V OC) and energy loss. Herein, hydrophobic poly(3-hexylthiophene) (P3HT) molecule is incorporated into a hole transport layer to interact with undercoordinated Pb2+ and promote ion diffusion in a confined space, resulting in higher-quality thin single crystals with reduced interface and bulk defect density, suppressed nonradiative recombination, accelerated charge transport, and extraction. As a result, a remarkably enhanced V OC of up to 1.13 V and efficiency of 22.1% are achieved, which are both the highest values for MAPbI3 single-crystal solar cells. Moreover, the reduced defect density and suppressed carrier recombination lead to superior weak light response of the single-crystal solar cells after incorporation of P3HT, and an indoor photovoltaic efficiency of 39.2% at 1000 lux irradiation is obtained.
Direct phase transformation grain growth mechanism is demonstrated from a solution-processed chalcopyrite structured precursor film, which enables fabrication of a highly efficient CuIn(S,Se)2 (CISSe) solar cell near stoichiometric composition without the detrimental Cu2− x Se due to its high tolerance to the Cu/In ratio (from 0.90 to 1.05). By preliminary optimization, a 13.6% efficient CISSe device is fabricated from an N-methyl-pyrrolidone solution processed in ambient air.
Solution-processed Cu(In,Ga)(S,Se)2 solar cells have reached 18% efficiency but still remain much lower compared to state-of-the-art vacuum based solar cells. In comparison to vacuum deposited precursor films, which mostly consist of stacked metal and/or metal chalcogenide layers and takes a liquid Cu2− x Se assisted grain growth mechanism, solution-processed precursor films normally have a chalcopyrite structure that is already developed. Understanding the grain growth mechanism of solution-processed absorbers is crucial to control the electronic properties and further improve the device photovoltaic performance. Here, the grain growth mechanism of a N-methyl-pyrrolidone solution processed precursor film with composition from Cu-poor to Cu-rich is systematically investigated. Characterizations show that the chalcopyrite structured CuInS2 precursor film takes a direct phase transformation grain growth mechanism and forms the CuIn(S,Se)2 (CISSe) absorber without the presence of a detrimental Cu2− x Se phase with Cu/In ratio up to unit. Beyond the stoichiometric composition, the coexistence of Cu2− x Se facilitates grain growth but deteriorates device performance. The direct phase transformation mechanism not only avoids detrimental Cu2− x Se but also enables fabrication of a highly efficient CISSe device near stoichiometric composition with high tolerance to the Cu/In ratio (from 0.90 to 1.05). By preliminary optimization, a CISSe solar cell with an efficiency of 13.6% is achieved in ambient air with a Cu/In ratio of 0.93.
High-efficiency air-fabricated inverted CsPbI3 PSCs with a wide humidity operating window are realized via an in situ stabilizing strategy. During operation in humidity air, maleic anhydride (MAAD) molecules can convert harmful water erosions into a stabilizer to regulate crystallization and suppress phase transition of CsPbI3 film. The inverted devices realize champion efficiency of 19.25% with good stability and wide humidity operating window.
Inverted triiodine cesium lead (CsPbI3) perovskite solar cells (PSCs) are promising in photovoltaics owing to their ideal light absorption, non-volatile active layer, and avoidance of fragile Spiro-OmeTAD, especially as the top cell in tandem devices. However, they still exhibit far-lagging efficiency, and must be processed in a strictly controlled environment due to water-fearing CsPbI3. Here, a novel strategy to convert the harmful water erosions into an in situ stabilizer for efficient inverted CsPbI3 PSCs fabricated with a wide humidity operating window, is proposed. During air fabrication, maleic anhydride (MAAD) can react with water molecules in air to reduce moisture erosions, while the hydrolysis products (maleic acid, MAAC) control grains growth. After annealing, MAAC strongly binds to CsPbI3 grains as a shield to hamper phase transition and moisture penetration. A champion efficiency of 19.25% is obtained, which is the highest efficiency among the inverted inorganic PSCs. In parallel, the authors’ optimized devices present efficiency of 18.39% even fabricated in relative humidity 60% condition. Moreover, the stability against various ages is improved, and the optimized devices remain at 96.8% of its initial efficiency after maximum power point tracking at 65 °C for 850 h.
Publication date: March 2022
Source: Nano Energy, Volume 93
Author(s): Yue Zhang, Baoqi Wu, Yakun He, Wanyuan Deng, Jingwen Li, Junyu Li, Nan Qiao, Yifan Xing, Xiyue Yuan, Ning Li, Christoph J. Brabec, Hongbin Wu, Guanghao Lu, Chunhui Duan, Fei Huang, Yong Cao
25 cm2 organic solar module based on PM6:BTP-eC9 processed from the high boiling point solvent (chlorobenzene) is fabricated with an efficiency of over 14%. The large side chain on the pyrrole ring of Y6-based nonfullerene can inhibit the excessive aggregation and obtain the wide processing window for doctor blading.
It is still challenging to fabricate efficient large-area organic solar modules by solution processing. Processing window is important to obtain optimal aggregation of an active layer in large area for high efficiency. The star active layer of PM6:Y6 is processed from chloroform (for high efficiency) that has a narrow processing window due to the low boiling point of the solvent. In this work, the correlation between chemical structure (side chains) and processing solvents is investigated to obtain high efficiency and long processing windows. It is found that large side chains on the pyrrole ring are the key factor influencing the aggregation of active layer films. Short side chain (in Y6 and Y6-1O) will cause excess aggregation when processed from high-boiling-point solvent (chlorobenzene, CB), while long side-chain (in BTP-BO-4F, BTP-BO-4Cl, and BTP-eC9) can inhibit such aggregation and maintain high photovoltaic performance when processed from CB with wide processing window. In the end, over 25 cm2 organic solar module via doctor blading based on PM6:BTP-eC9 active layer has been fabricated with a PCE of 14.07%.
Silicon heterojunction cells with bulk resistivities of 15 000 Ωcm can withstand low illumination intensities and accomplish breakdown voltages over −1000 V, almost two orders of magnitude larger than most commercial cells. Higher breakdown voltages can improve the reliability of modules in case of bypass-diode failure and reduce the module cost by easing the number of bypass-diodes required.
Recent developments in industry on surface passivation open the possibility of using less doped substrates in silicon solar cells. We investigate how the bulk resistivity affects the performance of silicon cells and the reliability of modules. Herein, n- and p-type silicon heterojunction cells with bulk resistivities between 3 and 15 000 Ωcm are studied. We measure the current–voltage characteristics of n-type cells across the resistivity range, and we find comparable responses to illumination intensities between 0.1 and 1 suns. The cells with bulk resistivities over 1000 Ωcm show breakdown voltages larger than −1000 V, almost two orders of magnitude higher than in typical commercial cells. Although modules have bypass-diodes to prevent cells from going into breakdown, higher breakdown voltages can improve the reliability of modules in case of bypass-diode failure and reduce the module cost by easing the number of bypass-diodes required. Finally, the cells have been submitted to light soaking. The float-zone p-type cells with bulk resistivities over 10 000 Ωcm are less sensitive to light-induced degradation than cells with bulk resistivities below 10 Ωcm. The former show to recover few hours after light soaking, while the latter recover only after dark annealing.
The multistrategy of ThMAAc addition and BTCIC-4Cl modification to prepare CsPbI2Br perovskite solar cells based on dopant-free poly(3-hexylthiophene) (P3HT) is applied. The multi-optimization can shrink the crystal lattice, release stress, passivate defects, and promote carrier transport, thereby obtaining a smaller open-circuit voltage deficit, a champion power conversion efficiency of 16.3% and excellent thermal stability.
All-inorganic perovskites have attracted substantial interest due to their outstanding thermal stability. However, the device performance is still inferior to the typical organic–inorganic counterparts because of the unsatisfying phase stability and defects of the inorganic perovskite films. Herein, a multistrategy to optimize CsPbI2Br perovskite solar cells (PSCs) based on dopant-free poly(3-hexylthiophene) (P3HT) by applying thienylmethylamine acetate additive to enhance the α phase stability and passivate the bulk defects of CsPbI2Br perovskite is successfully demonstrated, followed by implementing BTCIC-4Cl interlayer at CsPbI2Br/P3HT interface, which can coordinate with both perovskite and P3HT to suppress the surface defects and promote the hole transport. Benefitting from these, a champion power conversion efficiency (PCE) of 16.3% is achieved, and the unencapsulated optimized device can retain 97% of the initial PCE after aging under N2 atmosphere at 85 °C for 530 h. This work opens up a new era of multistrategy for improving performance and stability of CsPbI2Br PSCs based on dopant-free hole transport layer.
Nature Energy, Published online: 22 December 2021; doi:10.1038/s41560-021-00949-9
The efficiency of perovskite solar cells decreases over time, yet the underlying mechanisms are unclear. Ni et al. observe charged iodide interstitial defects within the device layers and how they contribute to the efficiency degradation when the cell is operated under illumination or reverse bias.
A functionalized polyurethane is used as an additive to self-heal a CsPbIBr2 film by a disulfide-exchange reaction upon heat treatment. The inorganic CsPbIBr2 perovskite solar cell achieves a champion efficiency of 10.61 % with efficiency recovery after heat treatment.
One great challenge for perovskite solar cells (PSCs) lies in their poor operational stability under harsh stimuli by humidity, heat, light, etc. Herein, a thermal-triggered self-healing polyurethane (PU) is tailored to simultaneously improve the efficiency and stability of inorganic CsPbIBr2 PSCs. The dynamic covalent disulfide bonds between adjacent molecule chains in PU at high temperatures self-heal the in-service formed defects within the CsPbIBr2 perovskite film. Finally, the best device free of encapsulation achieves a champion efficiency up to 10.61 % and an excellent long-term stability in an air atmosphere over 80 days and persistent heat attack (85 °C) over 35 days. Moreover, the photovoltaic performances are recovered by a simple heat treatment.
A series of regioregular polymer acceptors with different molecular weights are developed and the relationship between batch factors and properties is studied without isomer interference. PA-5 has unique absorption and better crystallization, which produces state-of-the-art binary all-polymer solar cells with a high efficiency of 16.11%. PA-6-L/M presents negligible batch difference in performance (close to 15%), while PA-6-H displays inferior efficiency.
Random conjugated polymers, such as typical polymerized small molecular acceptors (PSMAs), concurrently suffer from the dual batch factors of molecular weights (MWs) and regioregularity, which seriously interfere with the study of the relationship between batch factors and polymer properties. Here, four isomer-free PSMAs, PA-5 and three members of a PA-6 series with low (L), medium (M), and high (H) MWs, in which 5 and 6 define linkage position throughout conjugated backbone, are designed and synthesized to clearly investigate polymer batch effects. These studies reveal that PA-6-L and PA-6-M have ignorable batch differences within deviations, which deliver comparable maximum efficiencies of 14.81% and 14.99%, respectively. The PA-6-H based cell is processed from chlorobenzene with its high boiling point, due to the limited solubility in other common solvents, leading to large-size phase separation during prolonged film drying process, and thereby inferior performance. In contrast, PA-5 possesses diverse absorption characteristics, and ordered crystallization, which prompts higher short-circuit current density and fill factor in the cell. As a result, the corresponding device realizes a photovoltaic performance of 16.11%, which is one of the best binary all-polymer solar cells in the reported literature to date. This study provides a new insight into complicated batch effects of PSMAs on device performance while avoiding cross-talk between them.
A novel solution-printing strategy based on meniscus-assisted coating for all-polymer solar cells (all-PSCs) is presented. The champion device based on PM6:PY-IT shows a power conversion efficiency (PCE) of 15.53%, which is attributable to the enhanced crystallinity and nanofiber network morphology. It is worth mentioning that 15.53% is the highest PCE reported for solution-printing-based all-PSCs.
Morphology control is the key to engineering highly efficient solution-processed solar cells. Focusing on the most promising application-oriented photovoltaic all-polymer solar cells (all-PSCs), herein a facile and effective meniscus-assisted-coating (MAC) strategy is reported for preparing high-quality blend films with enhanced crystallinity and an interpenetrating nanofiber network morphology. The all-PSCs based on MAC exhibit excellent optoelectronic properties with efficiencies exceeding 15%, which is the best performance of solution-printing-based all-PSCs, as well as better stability. The crystallization kinetics of the polymer blend film is investigated by in situ UV–vis absorption spectroscopy, and the result explains the linear relationship between the meniscus advance speed and the crystallinity (crystallization rate) of the polymer. To verify the compatibility and universality of this strategy, the MAC strategy is applied to the other three binary systems. By precisely controlling the meniscus advancing speed, 1 cm2 all-PSC devices whose efficiencies exceed 12% are fabricated. Such progress demonstrates that the application of the MAC strategy is a promising approach for the fabrication of high-efficiency all-PSCs.
Ionic motion is known to impact perovskite solar cells' performance and leads to the appearance of hysteresis in the current–voltage characteristics. However, there is no simple method to quantify their impact on the stabilized performance. Herein, a new method is presented to measure the ion-free efficiency and determine the loss due to the ions.
Perovskite semiconductors differ from most inorganic and organic semiconductors due to the presence of mobile ions in the material. Although the phenomenon is intensively investigated, important questions such as the exact impact of the mobile ions on the steady-state power conversion efficiency (PCE) and stability remain. Herein, a simple method is proposed to estimate the efficiency loss due to mobile ions via “fast-hysteresis” measurements by preventing the perturbation of mobile ions out of their equilibrium position at fast scan speeds ( ≈ 1000 V s−1). The “ion-free” PCE is between 1% and 3% higher than the steady-state PCE, demonstrating the importance of ion-induced losses, even in cells with low levels of hysteresis at typical scan speeds ( ≈ 100 mV s−1). The hysteresis over many orders of magnitude in scan speed provides important information on the effective ion diffusion constant from the peak hysteresis position. The fast-hysteresis measurements are corroborated by transient charge extraction and capacitance measurements and numerical simulations, which confirm the experimental findings and provide important insights into the charge carrier dynamics. The proposed method to quantify PCE losses due to field screening induced by mobile ions clarifies several important experimental observations and opens up a large range of future experiments.
This review introduces various optical coupling structures for semitransparent organic and perovskite solar cells. Furthermore, different optimization strategies for materials of transparent electrodes (metal nanowires, carbon-based materials, and conductive polymers) are summarized in detail. This review article aims to give readers a better understanding of light management methods and transparent electrode optimization strategies for semitransparent organic and perovskite solar cells.
Comparing with inorganic solar cells, organic solar cells and perovskite solar cells have attracted considerable attention owing to their unique properties such as the color tunability of their photoactive layers, low cost, catering to solution processing, and flexibility, which have been considered as the most promising technologies in wearable energy resources and show huge potential in fabricating transparent devices. In recent years, numerous light coupling constructions and transparent electrode optimization strategies have been applied to further enhance device photoelectric performance. In this review, common strategies focusing on light modulation and for semitransparent organic solar cells and semitransparent perovskite solar cells, which are crucial to increase J sc, achieving adjustable chromaticity coordinates, high average visible transmittance and color rendering index have been summarized in detail.
Herein, one dimensional (1D) trimethylsulfonium lead triiodide (Me3SPbI3) nanoarrays are synthesized in aqueous condition with excellent water resistivity and environmental stability. Moreover, an efficient and stable 1D/3D device with power conversion efficiency (PCE) of 22.06% is demonstrated, which also maintains 97% of its initial value after 1000 h storage under ambient condition (RH ≈50%) without encapsulation.
Heterojunctions constructed upon multidimensional perovskites (1D/3D or 2D/3D) has emerged as an effective approach to improve the photovoltaic performance and stability of perovskite solar cells (PSCs). Herein, 1D trimethyl sulfonium lead triiodide (Me3SPbI3) 1D Me3SPbI3 nanoarrays are successfully synthesized via a two-step method in aqueous condition, which reflects excellent water resistivity and environmental stability. By incorporating this 1D Me3SPbI3 into lead halide 3D perovskites, heterostructural 1D/3D perovskite photoactive layer with improved morphology, crystallinity, enhanced photoluminescence lifetime, and reduced carrier recombination in comparison to its 3D counterpart is obtained. Moreover, an efficient and stable 1D/3D PSCs with power conversion efficiency (PCE) of 22.06% by using this 1D/3D perovskite are demonstrated. It noticeably maintained 97% of their initial efficiency after 1000 h storage under ambient condition (RH≈50%) without encapsulation. Our study opens up the design protocol for the development of next-generation highly efficient and stable perovskite solar cells.
