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Charge Carrier Collection and Contact Selectivity in Solar Cells
摘要： The electronic properties of the contacts to a photovoltaic absorber material are important for the final efficiency of any type of solar cell. For highly efficient solar cells based on high quality absorber materials like single-crystalline silicon, polycrystalline Cu(In,Ga)Se2, CdTe, or metal-halide perovskites, contact formation is even the decisive processing step determining the final efficiency. The present paper combines recently developed quantitative concepts for the description of contacts to solar cells in terms of their selectivity toward a more general description that is valid for all types of solar cells and all types of contacts. It is shown that the built-in voltage is an important parameter to influence the selectivity of contacts to photovoltaic absorber materials. It is also shown that the contact selectivity is mathematically related to the collection efficiency which can be measured by luminescence based techniques.
关键词： solar cells,charge extraction,surface recombination,photovoltaics,interface recombination
更新于2025-09-19 17:13:59
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A universal approach for optimizing charge extraction in electron transporting layer-free organic solar cells <i>via</i> Lewis base doping
摘要： Although the improvement of power conversion efficiency (PCE) in organic photovoltaic cells (OSC) is due to the development of novel donors and non-fullerene acceptors, state-of-the-art devices commonly utilize charge transporting/extraction interlayers. Here we demonstrate a universal approach based on a series of tetraalkyl ammonium bromide (TXABr) Lewis bases as n-dopants for mediating electron extracting properties in a range of OSCs with non-fullerene or PCBM acceptors. Under optimal conditions, the TXABr-doped devices without electron transporting layers (ETLs) exhibit PCEs comparable to those of the ones based on a conventional device structure containing ETLs. We found that the doping efficiency of acceptors is intimately correlated with the chain length (Lchain) of dopants. In OSCs based on acceptors of ITIC derivatives (IT-4F, ITIC, ITM, and ITCC), similar Lchain-dependent doping efficiency and PCE modification are found, while for OSCs with acceptors bearing different structures in conjugated backbones or side chains, the selection rule of dopants to achieve the best performance enhancement is different. These correlations are explained by the mutual effects of electrostatic interaction in the dopants and steric hindrance between the dopants and acceptors, the latter of which is affected by the compatibility of side chains in the host and dopant. With TXABr doping, (quasi-)ohmic contacts for electrons are realized in these ETL-free devices, leading to expediting the charge sweepout with mitigated interfacial charge recombination. This work offers a promising pathway to realize high efficiency non-fullerene OSCs with simplified device architecture.
关键词： organic solar cells,power conversion efficiency,charge extraction,Lewis base doping,electron transporting layer-free
更新于2025-09-16 10:30:52
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Perovskite Quantum Dot Solar Cells with 15.6% Efficiency and Improved Stability Enabled by an α-CsPbI <sub/>3</sub> /FAPbI <sub/>3</sub> Bilayer Structure
摘要： We developed lead halide perovskite quantum dot (QD) solar cells with a combinational absorbing layer based on stacked α-CsPbI3 and FAPbI3. α-CsPbI3 QDs, with a relatively wide bandgap of 1.75 eV, are not ideal for single-junction solar cells. We show that the absorption can be broadened by the introduction of another QD layer with a narrower bandgap like FAPbI3. The α-CsPbI3/FAPbI3 structure together with thermal annealing can improve the electrical coupling in the FAPbI3 layer and induce A-site cation exchange to develop a graded heterojunction for more efficient charge extraction. A highest power conversion efficiency of 15.6% and improved ambient stability have been achieved for the bilayer structured solar cells. More interestingly, the perovskite QDs provided a facile way to fabricate multiple layers and quantum junctions for optoelectronic applications via layer-by-layer deposition, which cannot be realized in solution-processed perovskite thin-film devices.
关键词： bilayer structure,perovskite quantum dot,ambient stability,solar cells,charge extraction,α-CsPbI3,FAPbI3
更新于2025-09-16 10:30:52
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Polyfluorene Copolymers as High‐Performance Hole Transport Materials for Inverted Perovskite Solar Cells
摘要： Inverted perovskite solar cells (PSCs) that can be entirely processed at low temperatures have attracted growing attention owing to their cost-effective production. Hole-transport materials (HTMs) play an essential role in achieving efficient inverted PSCs, as they determine the effectiveness of charge extraction and recombination at interfaces. In this study, three polyfluorene copolymers (TFB, PFB and PFO) were investigated as HTMs for construction of inverted PSCs. It is found that the photovoltaic performance of the solar cells is closely correlated with the electronic properties of the HTMs. Owing to its high mobility along with the favored energy level alignment with perovskite, TFB showed superior charge extraction and suppressed interfacial recombination than PFB- and PFO-based devices, which delivers a high efficiency of 18.48% with an open-circuit voltage (VOC) of up to 1.1 V. In contrast, the presence of a large energy barrier in the PFO-based devices resulted in substantial losses in both VOC and photocurrent. These results demonstrate that TFB could serve as a superior HTM for inverted PSCs. Moreover, we anticipate that the performance of the three HTMs identified here might guide molecular design of novel HTMs for the manufacture of highly efficient inverted PSCs.
关键词： hole-transport materials,charge extraction,polyfluorene copolymers,photovoltaic performance,inverted perovskite solar cells
更新于2025-09-12 10:27:22
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Advanced modification of perovskite surfaces for defect passivation and efficient charge extraction in air-stable CsPbBr3 perovskite solar cells
摘要： All-inorganic cesium lead bromide (CsPbBr3) halide has attracted growing attentions for carbon-based perovskite solar cells (PSCs) owing to its inherent stable lattice in thermal and/or moisture ambient. The main drawback for carbon-based CsPbBr3 PSCs is the low power conversion efficiency (PCE) caused by serious charge recombination at perovskite surface and/or device interfaces. To address this problem, an interface engineering strategy by modifying a polyvinyl acetate (PVAc) polymer with carbonyl group at the interface of CsPbBr3/carbon is implemented to passivate perovskite surface defect states and also to improve energy level alignment between valence band of CsPbBr3 and work function of carbon, suppressing charge recombination and accelerating charge separation. By introducing graphene oxide (GO) layer for further promoting hole extraction and decreasing energy level difference, the PSC with an architecture of FTO/c-TiO2/m-TiO2/CsPbBr3/PVAc/GO/carbon achieves a champion PCE as high as 9.53%, yielding an improvement by 44.0% compared with 6.62% for the original device. Furthermore, the optimal device free of encapsulation exhibits remarkable long-term stability under high humidity, high temperature and continuous illumination in air. This work provides a new polymer as interface modification material for reducing defect states as well as enhancing energy level alignment and suggests an effective approach for fabricating efficient and stable carbon-based CsPbBr3 PSCs.
关键词： Graphene oxide,CsPbBr3 perovskite solar cells,Interface modification,Charge extraction,Polyvinyl acetate
更新于2025-09-12 10:27:22
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Charge Transport and Extraction of Bilayer Interdiffusion Heterojunction Organic Solar Cells
摘要： Bilayer interdiffusion heterojunction with the structure of donor-rich region near the anode and acceptor-rich region near the cathode, could weaken energy level barrier between active layer and electrode, and improve the performance of organic solar cells. In this study, the poly (3-hexylthiophene) (P3HT) / [6:6]-phenyl-C61-butyric acid (PC61BM) bilayer interdiffusion heterojunction organic solar cells were prepared by using orthogonal solvent method, and the charge transport and extraction characteristics were investigated detailedly. The transient photovoltage/transient photocurrent measurements showed that the bilayer interdiffusion heterojunction devices have longer carrier recombination lifetime and shorter charge extract time, and higher carrier mobility of bilayer interdiffusion device was verified by photo-induced charge carrier extraction by linearly increasing voltage technology. The results indicated that the improved heterojunction structure of bilayer interdiffusion devices could reduce carrier recombination and improve charge transport and extraction efficiency. The performance of bilayer interdiffusion device was enhanced obviously, and about 19.8 % power conversion efficiency improvement was achieved as compared with the bulk device. Bilayer interdiffusion heterojunction provide an efficient device structure to optimize performance of organic solar cells.
关键词： Bilayer interdiffusion heterojunction,PC61BM,organic solar cells,P3HT,charge extraction,charge transport
更新于2025-09-11 14:15:04
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Titanium-carbide MXenes for work function and interface engineering in perovskite solar cells
摘要： To improve the efficiency of perovskite solar cells, careful device design and tailored interface engineering are needed to enhance optoelectronic properties and the charge extraction process at the selective electrodes. Here, we use two-dimensional transition metal carbides (MXene Ti3C2Tx) with various termination groups (Tx) to tune the work function (WF) of the perovskite absorber and the TiO2 electron transport layer (ETL), and to engineer the perovskite/ETL interface. Ultraviolet photoemission spectroscopy measurements and density functional theory calculations show that the addition of Ti3C2Tx to halide perovskite and TiO2 layers permits the tuning of the materials’ WFs without affecting other electronic properties. Moreover, the dipole induced by the Ti3C2Tx at the perovskite/ETL interface can be used to change the band alignment between these layers. The combined action of WF tuning and interface engineering can lead to substantial performance improvements in MXene-modified perovskite solar cells, as shown by the 26% increase of power conversion efficiency and hysteresis reduction with respect to reference cells without MXene.
关键词： work function,charge extraction,interface engineering,perovskite solar cells,MXene,TiO2
更新于2025-09-11 14:15:04
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π-Conjugated small molecules enable efficient perovskite growth and charge-extraction for high-performance photovoltaic devices
摘要： A π-conjugated small molecule N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)benzidine (NPB) is introduced into a poly (bis(4-phenyl)(2,4,6-trimethylphenyl)amine) (PTAA) hole transport layer in inverted perovskite solar cells (PSCs). The NPB doping induces better perovskite crystal growth owing to a strong π-π interaction with PTAA and cation-π interactions with CH3NH3+ (MA+). In addition, NPB doping not only improves the wettability of PTAA and regulates the perovskite crystallization to achieve a larger grain size, but also moves the valence band energy of the hole transport layer closer to the perovskite layer. Consequently, the fabricated PSCs delivered a power conversion efficiency (PCE) of 20.15%, with a short-circuit current density (JSC) of 22.60 mA/cm2 and open-circuit voltage (VOC) of 1.14 V. This outcome indicates that PTAA:NPB composite materials present great potential for fabricating high-performance PSCs.
关键词： Energy level alignment,Charge extraction,π-conjugated molecule
更新于2025-09-11 14:15:04
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Improving and Stabilizing Perovskite Solar Cells with Incorporation of Graphene in the Spiro-OMeTAD Layer: Suppressed Li Ions Migration and Improved Charge Extraction
摘要： Perovskite solar cells (PSCs) have achieved a huge success in power conversion efficiency (PCE), while they still suffer from the long-term stability problem caused by the intrinsic sensitivity of perovskites to moisture. 2,2’,7,7’-tetrakis (N, N-di-p-methoxyphenylamine) 9,9’-spirobifluorene (Spiro-OMeTAD) is widely used as the hole transport layer (HTL) in typical PSCs; meanwhile bis(trifuoromethane)sulfonimide lithium salt (Li-TFSI) proves its necessity as an additive in the Spiro-OMeTAD HTL to improve the hole mobility. However, the Li+ ions bring in high hygroscopicity and water-uptake effect that both aggravate degradation of the Spiro-OMeTAD HTL and thereby of the perovskite layers. Here, we modify the Li-TFSI-based Spiro-OMeTAD HTL by adding reduced graphene oxide (rGO). We verify that rGO provides adsorption sites for Li+ ions and subsequently suppresses Li+ migration. The water-uptake effect originated from Li+ ions is thus relieved and detestable pinholes in HTL caused by Li+ ion migration are eliminated. Consequently, the rGO-incorporated HTL remarkably improves the device stability that maintains the initial PCEs within 3% loss after 700 h under 40% humidity; whereas the pristine devices almost lose the efficiency after 620 h. In addition, the good conductivity of the rGO favors hole transport in the Spiro-OMeTAD, resulting in a promotion in PCEs from 17.7% to 19.3% by incorporating rGO in HTL. Our work takes an insight into the function of rGO in the HTL and demonstrates an effective way of improving the efficiency and stability of PSCs simultaneously.
关键词： Perovskite solar cells,lithium ions,moisture stability,reduced graphene oxide (rGO),charge extraction,ion migration
更新于2025-09-11 14:15:04
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Effects of Organic Cations on Carrier Transport at the Interface between Perovskites and Electron Transport Layers in (FA,MA)SnI <sub/>3</sub> Solar Cells
摘要： Charge extraction at carrier transport layers adjacent to perovskites is crucial for the optimization of perovskite solar cells. In particular, Sn–perovskites with no lead elements are known to struggle from charge extraction. Here, we report the effects of organic ligands like FA and MA (FA = HC(NH2)2+; MA = CH3NH3+) on charge separation at the interface between electron transport layers and perovskites. TiO2 mesoporous covering the tin-perovskites show significant changes in electronic structure and built–in potentials according to the ratio of FA to MA. Through a local probe with potential and current mapping, charge transport has been intensively examined. The best cell in this study is obtained as 5.37% at FA : MA = 3 : 1 with only iodine at the halide sites. Even though the value itself is not comparable with lead halides but it could pave a new direction to improve lead–free perovskite solar cells.
关键词： perovskite solar cells,tin perovskites,TiO2 mesoporous,charge extraction,organic cations
更新于2025-09-11 14:15:04