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With the rapid development of perovskite solar cells, reducing losses in open‐circuit voltage (Voc) is a key issue in efforts to further improve device performance. Here it is focused on investigating the correlation between the highest occupied molecular orbital (HOMO) of device hole transport layers (HTLs) and device Voc. To achieve this, structurally similar HTL materials with comparable optical band gaps and doping levels, but distinctly different HOMO levels are employed. Using light‐intensity dependent Voc and photoluminescence measurements significant differences in the behavior of devices employing the two HTLs are highlighted. Light‐induced increase of quasi‐Fermi level splitting (ΔEF) in the perovskite layer results in interfacial quasi‐Fermi level bending required to align with the HOMO level of the HTL, resulting in the Voc measured at the contacts being smaller than the ΔEF in the perovskite. It is concluded that minimizing the energetic offset between HTLs and the perovskite active layer is of great importance to reduce non‐radiative recombination losses in perovskite solar cells with high Voc values that approach the radiative limit. The role of the hole transport layer (HTL) highest occupied molecular orbital (HOMO) energy on device open‐circuit voltage (Voc) is explored. Light‐intensity‐dependent photoluminescence spectroscopy shows that as light intensity increases the HOMOHTL begins to limit the achievable Voc. It is shown this as a consequence of increases in the magnitude of the quasi‐Fermi level splitting in the bulk perovskite resulting in greater upward bending of the hole quasi‐Fermi level (EF, p) in the HTL.

Power conversion efficiency (PCE) of single-junction polymer solar cells (PSCs) has made a remarkable breakthrough recently. Plenty of work was reported to achieve PCEs higher than 16% derived from the PM6:Y6 binary system. To further increase the PCEs of binary OSCs incorporating small molecular acceptor (SMA) Y6, we substituted PM6 with PM7 due to the deeper highest occupied molecular orbital (HOMO) of PM7. Consequently, the PM7:Y6 has achieved PCEs as high as 17.0% by the hotcast method, due to the improved open-circuit voltage (VOC). Compared with PM6, the lower HOMO of PM7 increases the gap between E LUMO-donor and E HOMO-acceptor , which is proportional to V OC . This research provides a high PCE for single-junction binary PSCs, which is meaningful for device fabrication related to PM7 and commercialization of PSCs.

Antimony selenide (Sb2Se3) is an ideal photovoltaic candidate profiting from its advantageous material characteristics and superior optoelectronic properties, and has gained considerable development in recent years. However, the further device efficiency breakthrough is largely plagued by severe open‐circuit voltage (VOC) deficit under the existence of multiple defect states and detrimental recombination loss. In this work, an effective absorber layer growth engineering involved with vapor transport deposition and post‐selenization is developed to grow Sb2Se3 thin films. High‐quality Sb2Se3 with large compact crystal grains, benign [hk1] growth orientation, stoichiometric chemical composition, and suitable direct bandgap are successfully fulfilled under an optimized post‐selenization scenario. Planar Sb2Se3 thin‐film solar cells with substrate configuration of Mo/Sb2Se3/CdS/ITO/Ag are constructed. By contrast, such engineering effort can remarkably mitigate the device VOC deficit, owing to the healed detrimental defects, the suppressed interface and space‐charge region recombination, the prolonged carrier lifetime, and the enhanced charge transport. Accordingly, a minimum VOC deficit of 0.647 V contributes to a record VOC of 0.513 V, a champion device with highly interesting efficiency of 7.40% is also comparable to those state‐of‐the‐art Sb2Se3 solar cells, paving a bright avenue to broaden its scope of photovoltaic applications. A two‐step thermodynamic/kinetic deposition process involving vapor transport deposition and post‐selenization is developed to grow high‐quality Sb2Se3 thin films. Such absorber engineering can heal detrimental defects, prolong carrier lifetime, suppress interface, and space‐charge region recombination. Thus, the substrate structured Mo/Sb2Se3/CdS/ITO/Ag solar cell delivers a record open‐circuit voltage (VOC) of 0.513 V with minimum deficit, and highly competitive efficiency of 7.40%.

As a promising candidate for low‐cost and environmentally friendly thin‐film photovoltaics, the emerging kesterite‐based Cu2ZnSn(S,Se)4 (CZTSSe) solar cells have experienced rapid advances over the past decade. However, the record efficiency of CZTSSe solar cells (12.6%) is still significantly lower than those of its predecessors Cu(In,Ga)Se2 (CIGS) and CdTe thin‐film solar cells. This record has remained for several years. The main obstacle for this stagnation is unanimously attributed to the large open‐circuit voltage (VOC) deficit. In addition to cation disordering and the associated band tailing, unpassivated interface defects and undesirable energy band alignment are two other culprits that account for the large VOC deficit in kesterite solar cells. To capture the great potential of kesterite solar cells as prospective earth‐abundant photovoltaic technology, current research focuses on cation substitution for CZTSSe‐based materials. The aim here is to examine recent efforts to overcome the VOC limit of kesterite solar cells by cation substitution and to further illuminate several emerging prospective strategies, including: i) suppressing the cation disordering by distant isoelectronic cation substitution, ii) optimizing the junction band alignment and constructing a graded bandgap in absorber, and iii) engineering the interface defects and enhancing the junction band bending. Cation substitution is one of the most promising solutions to overcome the large open‐circuit voltage (VOC) deficit in kesterite solar cells. This deficit is attributed to cation disorder and associated band tailing, unpassivated interfaces, and undesirable energy band alignment. Recent efforts and strategies are considered to overcome the VOC limit of kesterite solar cells using various cation substitution methods.

The tuning of vertical morphology is critical and challenging for organic solar cells (OSCs). In this work, a high open‐circuit voltage (VOC) binary D18‐Cl/L8‐BO system is attained while maintaining the high short‐circuit current (JSC) and fill factor (FF) by employing 1,4‐diiodobenzene (DIB), a volatile solid additive. It is suggested that DIB can act as a linker between donor or/and acceptor molecules, which significantly modifies the active layer morphology. The overall crystalline packing of the donor and acceptor is enhanced, and the vertical domain sizes of phase separation are significantly decreased. All these morphological changes contribute to exciton dissociation, charge transport, and collection. Therefore, the best‐performing device exhibits an efficiency of 18.7% with a VOC of 0.922 V, a JSC of 26.6 mA cm−2, and an FF of 75.6%. As far as it is known, the VOC achieved here is by far the highest among the reported OSCs with efficiencies over 17%. This work demonstrates the high competence of solid additives with two iodine atoms to tune the morphology, particularly in the vertical direction, which can become a promising direction for future optimization of OSCs. The solid additive, 1,4‐diiodobenzene (DIB), has a high competence to optimize the vertical morphology of bulk heterojunction active layer, resulting in a high efficiency of 18.7% with a open‐circuit voltage (VOC) of 0.922 V, a short‐circuit current (JSC) of 26.6 mA cm−2, and a fill factor (FF) of 75.6% for DIB‐processed D18‐Cl/L8‐BO binary devices.

Antimony chalcogenides, including Sb2S3, Sb2Se3, and Sb2(S,Se)3, have been developed as attractive non‐toxic and earth‐abundant solar absorber candidates among the thin‐film photovoltaic devices. Presently, a record certified power conversion efficiency of 10.5% has been demonstrated for antimony chalcogenide solar cells, which is significantly lower than that of Cu2(In,Ga)Se2 (23.35%) and CdTe (22.1%) thin‐film solar cells. The inferior performance in antimony chalcogenide solar cells is mainly owing to a large open‐circuit voltage (VOC) deficit resulted from the defect and interface‐assisted recombination. Herein, a comprehensive review on the recent advancements interface band alignment and defect passivation are carried out. This review will provide a solid understanding on the interfaces and defects of antimony chalcogenide solar cells, which is beneficial to the research and development of such kind of solar cells. Trap‐assisted and interface‐induced recombination is recognized as the most prominent for the large VOC deficit of antimony chalcogenide solar cells. This review focused on summary and discussion on the recent progress of boosting VOC in antimony chalcogenide based‐solar cells. New breakthrough in band alignment optimization and defect passivation may hold the key to developing efficient and stable antimony chalcogenide solar cells.

Open circuit voltage (OCV) of lithium batteries has been of interest since the battery management system (BMS) requires an accurate knowledge of the voltage characteristics of any Li-ion batteries. This article presents an OCV characteristic for lithium manganese oxide (LMO) batteries under several experimental operating conditions, and discusses factors for accurate OCV determination. A test system is developed for OCV characterization based on the OCV pulse test method. Various factors for the OCV behavior, such as resting period, step-size of the pulse test, testing current amplitude, hysteresis phenomena, and terminal voltage relationship, are investigated and evaluated. To this end, a general OCV model based on state of charge (SOC) tracking is developed and validated with satisfactory results.

This paper proposes two new Maximum Power Point Tracking (MPPT) methods which improve the conventional Fractional Open Circuit Voltage (FOCV) method. The main novelty is a switched semi-pilot cell that is used for measuring the open-circuit voltage. In the first method this voltage is measured on the semi-pilot cell located at the edge of PV panel. During the measurement the semi-pilot cell is disconnected from the panel by a pair of transistors, and bypassed by a diode. In the second Semi-Pilot Panel method the open circuit voltage is measured on a pilot panel in a large PV system. The proposed methods are validated using simulations and experiments. It is shown that both methods can accurately estimate the maximum power point voltage, and hence improve the system efficiency.

The concept of bromination for organic solar cells has received little attention. However, the electron withdrawing ability and noncovalent interactions of bromine are similar to those of fluorine and chlorine atoms. A tetra‐brominated non‐fullerene acceptor, designated as BTIC‐4Br, has been recently developed by introducing bromine atoms onto the end‐capping group of 2‐(3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene) malononitrile and displayed a high power conversion efficiency (PCE) of 12%. To further improve its photovoltaic performance, the acceptor is optimized either by introducing a longer alkyl chain to the core or by modulating the numbers of bromine substituents. After changing each end‐group to a single bromine, the BTIC‐2Br‐m‐based devices exhibit an outstanding PCE of 16.11% with an elevated open‐circuit voltage of Voc = 0.88 V, one of the highest PCEs reported among brominated non‐fullerene acceptors. This significant improvement can be attributed to the higher light harvesting efficiency, optimized morphology, and higher exciton quenching efficiencies of the di‐brominated acceptor. These results demonstrate that the substitution of bromine onto the terminal group of non‐fullerene acceptors results in high‐efficiency organic semiconductors, and promotes the use of the halogen‐substituted strategy for polymer solar cell applications. The bromination of non‐fullerene acceptors provides a promising alternative approach for the creation of high‐performance organic solar cells. BTIC‐2Br‐m‐based devices exhibit an outstanding power conversion efficiency of 16.11% with an elevated open circuit voltage of 0.88 V, representing one of the highest efficiencies in brominated non‐fullerene acceptors.

This paper explores a novel group of D-π-A configurations that has been specifically created for organic solar cell applications. In these material compounds, the phenothiazine, the furan, and two derivatives of the thienyl-fused IC group act as the donor, the π-conjugated spacer, and the end-group acceptors, respectively. We assess the impact of substituents by introducing bromine atoms at two potential substitution sites on each end-group acceptor (EG1 and EG2). With the donor and π-bridge held constant, we have employed density functional theory and time-dependent DFT simulations to explore the photophysical and optoelectronic properties of tailored compounds (M1–M6). We have demonstrated how structural modifications influence the optoelectronic properties of materials for organic solar cells. Moreover, all proposed compounds exhibit a greater Voc exceeding 1.5 V, a suitable HOMO-LUMO energy gap (2.14–2.30 eV), and higher dipole moments (9.23–10.90 D). Various decisive key factors that are crucial for exploring the properties of tailored compounds—frontier molecular orbitals, transition density matrix, electrostatic potential, open-circuit voltage, maximum absorption, reduced density gradient, and charge transfer length (Dindex)—were also explored. Our analysis delivers profound insights into the design principles of optimizing the performance of organic solar cell applications based on halogenated material compounds.