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Minimizing Defect States in Lead Halide Perovskite Solar Cell Materials
摘要： In order to reach the theoretical e?ciency limits of lead-based metal halide perovskite solar cells, the voltage should be enhanced because it su?ers from non-radiative recombination. Perovskite materials contain intrinsic defects that can act as Shockley–Read–Hall recombination centers. Several experimental and computational studies have characterized such defect states within the band gap. We give a systematic overview of compositional engineering by distinguishing the di?erent defect-reducing mechanisms. Doping e?ects are divided into in?uences on: (1) crystallization; (2) lattice properties. Incorporation of dopant in?uences the lattice properties by: (a) lattice strain relaxation; (b) chemical bonding enhancement; (c) band gap tuning. The intrinsic lattice strain in undoped perovskite was shown to induce vacancy formation. The incorporation of smaller ions, such as Cl, F and Cd, increases the energy for vacancy formation. Zn doping is reported to induce strain relaxation but also to enhance the chemical bonding. The combination of computational studies using (DFT) calculations quantifying and qualifying the defect-reducing propensities of di?erent dopants with experimental studies is essential for a deeper understanding and unraveling insights, such as the dynamics of iodine vacancies and the photochemistry of the iodine interstitials, and can eventually lead to a more rational approach in the search for optimal photovoltaic materials.
关键词： semiconductor,solar energy,photovoltaics,doping,thin ?lm materials,voltage loss,stabilization,optimization,charge generation,light harvesting
更新于2025-09-23 15:21:01
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Reduced-dimensional perovskite photovoltaics with homogeneous energy landscape
摘要： Reduced-dimensional (quasi-2D) perovskite materials are widely applied for perovskite photovoltaics due to their remarkable environmental stability. However, their device performance still lags far behind traditional three dimensional perovskites, particularly high open circuit voltage (Voc) loss. Here, inhomogeneous energy landscape is pointed out to be the sole reason, which introduces extra energy loss, creates band tail states and inhibits minority carrier transport. We thus propose to form homogeneous energy landscape to overcome the problem. A synergistic approach is conceived, by taking advantage of material structure and crystallization kinetic engineering. Accordingly, with the help of density functional theory guided material design, (aminomethyl) piperidinium quasi-2D perovskites are selected. The lowest energy distribution and homogeneous energy landscape are achieved through carefully regulating their crystallization kinetics. We conclude that homogeneous energy landscape significantly reduces the Shockley-Read-Hall recombination and suppresses the quasi-Fermi level splitting, which is crucial to achieve high Voc.
关键词： homogeneous energy landscape,open circuit voltage loss,Reduced-dimensional perovskite,photovoltaics,Shockley-Read-Hall recombination
更新于2025-09-19 17:13:59
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The Origin of Open-Circuit Voltage Losses in Perovskite Solar Cells Investigated by Surface Photovoltage Measurement
摘要： Increasing the open circuit voltage (Voc) is one of the key strategies for further improvement of the efficiency of perovskite solar cells. It requires fundamental understanding of the complex optoelectronic processes related to charge carrier generation, transport, extraction and their loss mechanisms inside a device upon illumination. Herein we report the important origin of Voc losses in methylammonium lead iodide perovskite (MAPI) based solar cells, which results from undesirable positive charge (hole) accumulation at the interface between the perovskite photoactive layer and the PEDOT:PSS hole transport layer. We show strong correlation between the thickness-dependent surface photovoltage and device performance, unraveling that the interfacial charge accumulation leads to charge carrier recombination and results in a large decrease in Voc for the PEDOT:PSS/MAPI inverted devices (180 mV reduction in 50-nm-thick device compared to 230-nm-thick one). In contrast, accumulated positive charges at the TiO2/MAPI interface modify interfacial energy band bending, which leads to an increase in Voc for the TiO2/MAPI conventional devices (70 mV increase in 50-nm-thick device compared to 230-nm-thick one). Our results provide an important guideline for better control of interfaces in perovskite solar cells to improve device performance further.
关键词： solar cell,open circuit voltage,perovskite,voltage loss,surface photovoltage
更新于2025-09-16 10:30:52
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Mediated Non-geminate Recombination in Ternary Organic Solar Cells Through a Liquid Crystal Guest Donor
摘要： The approach via ternary blends prompts the increase of absorbed photon density and resultant photocurrent enhancement in organic solar cells (OSCs). In contrast to actively reported high efficiency ternary OSCs, little is known about charge recombination properties and carrier loss mechanisms in these emerging devices. Here, through introducing a small molecule donor BTR as a guest component to the PCE-10:PC71BM binary system, we show that photocarrier losses via recombination are mitigated with respect the binary OSCs, owing to a reduced bimolecular recombination. The gain of the fill factor in ternary devices are reconciled by the change in equilibrium between charge exaction and recombination in the presence of BTR toward the former process. With these modifications, the power conversion efficiency in ternary solar cells receives a boost from 8.8 (PCE-10:PC71BM) to 10.88%. We further found that the voltage losses in the ternary cell are slightly suppressed, related to the rising charge transfer-state energy. These benefits brought by the third guest donor are important for attaining improvements on key photophysical processes governing the photovoltaic efficiencies in organic ternary solar cells.
关键词： charge transfer states,small molecule donor,voltage loss,ternary solar cells,charge recombination
更新于2025-09-16 10:30:52
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Efficient perovskite solar cells through suppressed non-radiative charge carrier recombination by processing additive
摘要： It was reported that non-radiative charge carrier recombination in hybrid perovskite materials restricted device performance of perovskite solar cells. In this study, we report efficient perovskite solar cells through suppressed non-radiative charge carrier recombination by processing additive, aminopropanoic acid. It is found that aminopropanoic acid not only modulate the crystal growth processes, but also minimize defects of CH3NH3PbI3 thin films. Moreover, the CH3NH3PbI3 thin films processed with addition of aminopropanoic acid exhibit both enhanced photoluminescence and electroluminescence, elongated charge carrier lifetime, indicating that non-radiative charge carrier recombination within CH3NH3PbI3 thin films is drastically suppressed. As a result, perovskite solar cells fabricated by CH3NH3PbI3 thin films processed with addition of aminopropanoic acid exhibit approximatively 15% enhanced efficiency as compared with that by pristine CH3NH3PbI3 thin film. All these results demonstrate that our finding provides a facial way to improve efficiency of perovskite solar cells.
关键词： open-circuit voltage loss,perovskite solar cells,photoluminescence,electroluminescence,non-radiative charge carrier recombination
更新于2025-09-16 10:30:52
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Importance of interfacial crystallinity to reduce open-circuit voltage loss in organic solar cells
摘要： Reducing the energy loss in output voltage is critically important for further enhancing the ef?ciency of organic solar cells (OSCs). Here, we report that OSCs with high mobility and highly crystalline donor (D) and acceptor (A) materials were able to reduce an open-circuit voltage (VOC) loss. The crystallinity of the acceptor layer could be altered by appropriate selection of the three molecules with different alkyl side chain lengths. The VOC was found to increase as the crystallinity of the acceptor layer increased. The origin of the high VOC was that the highly crystalline D/A interface reduced the energy loss in the output voltage by realizing ideal band-to-band recombination. Especially, the high crystallinity of the several molecular layers (less than 6 nm) in the vicinity of the D/A interface was important for realizing the high VOC. Our results demonstrate that the careful design of the D/A interface enables high power conversion ef?ciencies to be achieved in OSCs by reducing open-circuit voltage loss.
关键词： power conversion efficiency,interfacial crystallinity,open-circuit voltage loss,organic solar cells,donor/acceptor interface
更新于2025-09-16 10:30:52
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Difluorobenzoxadiazole-based conjugated polymers for efficient non-fullerene polymer solar cells with low voltage loss
摘要： Two donor-acceptor (D-A) conjugated copolymers based on difluorobenzoxadiazole (ffBX) and oligothiophenes, i.e., PffBX-2T and PffBX-TT, were designed and synthesized for polymer solar cells (PSCs). Compared to the polymers based on difluorobenzothiadiazole (ffBT) units, the two ffBX-based polymers presented identical optical bandgaps (~1.62 eV), but lower highest occupied molecular orbital (HOMO) energy levels. Owing to the down-shifted HOMO levels, the PSCs based on PffBX-2T and PffBX-TT showed lower voltage loss, and the open-circuit voltage (Voc) was ~0.1 V higher than that of the devices with the ffBT-based polymer. As a result, higher photovoltaic performance was achieved for the devices based on the ffBX-based polymers. The power conversion efficiencies (PCEs) of the non-fullerene PSCs with PffBX-2T and PffBX-TT as the donor were 8.72% and 10.12%, respectively. The superior device performance of PffBX-TT resulted from the efficient exciton dissociation and charge transport as well as weak charge recombination, which could be ascribed to the favorable face-on packing of the conjugated backbones and the desired morphology in the blend film. Our study demonstrates that difluorobenzoxadiazole is a promising building block for constructing conjugated polymers for high-performance non-fullerene PSCs.
关键词： voltage loss,difluorobenzoxadiazole,alkylthiophene side chains,non-fullerene polymer solar cells
更新于2025-09-12 10:27:22
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Investigation on voltage loss in organic triplet photovoltaic devices based on Ir complexes
摘要： Voltage losses in singlet material-based organic photovoltaic devices (OPVs) have been intensively studied, whereas, only a few investigations on triplet material-based OPVs (T-OPVs) are reported. To investigate the voltage loss in T-OPVs, two homoleptic iridium(III) complexes based on extended p-conjugated benzo[g]phthalazine ligands, Ir(Ftbpa)3 and Ir(FOtbpa)3, are synthesized as sole electron donors. T-OPVs are fabricated by mixing two donors with phenyl-C71-butyric acid methyl ester (PC71BM) as an electron acceptor. Insertion of oxygen-bridges as flexible inert d-spacers in Ir(FOtbpa)3 has slightly elevated both the lowest unoccupied molecular orbital and the highest occupied molecular orbital levels compared to those of Ir(Ftbpa)3, which results in a lower charge transfer (CT) state energy (ECT) for Ir(FOtbpa)3-based devices. However, a higher Voc (0.88 V) is observed for Ir(FOtbpa)3-based devices than those of Ir(Ftbpa)3 (0.80 V). To understand the above result, the morphologies of the two blend films are studied, which excludes the influence of morphology. Furthermore, radiative and non-radiative recombination in two devices is quantitatively investigated, which suggests that a higher Voc can be attributed to reduced radiative and non-radiative recombination loss for the Ir(FOtbpa)3-based devices.
关键词： charge transfer state energy,organic photovoltaic devices,triplet material-based OPVs,radiative and non-radiative recombination,iridium(III) complexes,voltage loss
更新于2025-09-12 10:27:22
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Achieving Fast Charge Separation and Low Nonradiative Recombination Loss by Rational Fluorination for High‐Efficiency Polymer Solar Cells
摘要： Four low-cost copolymer donors of poly(thiophene-quinoxaline) (PTQ) derivatives are demonstrated with different fluorine substitution forms to investigate the effect of fluorination forms on charge separation and voltage loss (Vloss) of the polymer solar cells (PSCs) with the PTQ derivatives as donor and a A–DA’D–A-structured molecule Y6 as acceptor. The four PTQ derivatives are PTQ7 without fluorination, PTQ8 with bifluorine substituents on its thiophene D-unit, PTQ9, and PTQ10 with monofluorine and bifluorine substituents on their quinoxaline A-unit respectively. The PTQ8- based PSC demonstrates a low power conversion efficiency (PCE) of 0.90% due to the mismatch in the highest occupied molecular orbital (HOMO) energy levels alignment between the donor and acceptor. In contrast, the devices based on PTQ9 and PTQ10 show enhanced charge-separation behavior and gradually reduced Vloss, due to the gradually reduced nonradiative recombination loss in comparison with the PTQ7-based device. As a result, the PTQ10-based PSC demonstrates an impressive PCE of 16.21% with high open-circuit voltage and large short-circuit current density simultaneously, and its Vloss is reduced to 0.549 V. The results indicate that rational fluorination of the polymer donors is a feasible method to achieve fast charge separation and low Vloss simultaneously in the PSCs.
关键词： voltage loss,nonradiative recombination,low-cost copolymer donors,fluorination,charge separation
更新于2025-09-12 10:27:22
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High-efficiency organic solar cells with low voltage-loss of 0.46 V
摘要： The recent evolution of active components yielded brilliant progresses for organic solar cells (OSCs), yet the mechanism is needed to be clearly understood. In this work, two electron acceptors, a linear SN6-2Br and a V-shaped BTP-2Br, are developed with nitrogen atoms introduced to replace the traditional sp3-hybridized carbon in the fused ring. BTP-2Br possesses an electron-deficient central core, which exhibits slightly blue-shifted absorption as well as deepened HOMO-level compared with SN6-2Br. The corresponding photovoltaic performance from V-shaped BTP-2Br based devices exhibit superior performance especially in short-circuit current (Jsc), despite an enhanced absorption and charge carrier mobilities for SN6-2Br. The primary reason for the higher Jsc from BTP-2Br is faster exciton diffusion and dissociation in blends, than those of SN6-2Br. As a result, PBDB-TF:BTP-2Br based devices achieve a power conversion efficiency (PCE) of 13.84% with an voltage-loss of only 0.46 V, which is one of the lowest values ever reported. Moreover, we fabricated semitransparent OSCs that exhibit an excellent PCE of 9.62% with average visible transparency of 20.1%.
关键词： Organic solar cells,High efficiency,Semitransparent OSCs,Electron-deficient central core,Low voltage-loss
更新于2025-09-11 14:15:04