Deploying a Dipole Electric Field at the CsPbI3 Perovskite/Carbon Interface for Enhancing Hole Extraction and Photovoltaic Performance.

Carbon-based CsPbI3 perovskite solar cells without hole transporter (C-PSCs) have achieved intense attention due to its simple device structure and high chemical stability. However, the severe interface energy loss at the CsPbI3/carbon interface, attributed to the lower hole selectivity for inefficient charge separation, greatly limits device performance. Hence, dipole electric field (DEF) is deployed at the above interface to address the above issue by using a pole molecule, 4-trifluoromethyl-Phenylammonium iodide (CF3-PAI), in which the ─NH3 group anchors on the perovskite surface and the ─CF3 group extends away from it and connects with carbon electrode. The DEF is proven to align with the built-in electric field, that is pointing toward carbon electrode, which well enhances hole selectivity and charge separation at the interface. Besides, CF3-PAI molecules also serve as defect passivator for reducing trap state density, which further suppresses defect-induced non-radiative recombination. Consequently, the CsPbI3 C-PSCs achieve an excellent efficiency of 18.33% with a high VOC of 1.144 V for inorganic C-PSCs without hole transporter.

Spatially selective defect management of CsPbI3 films for high-performance carbon-based inorganic perovskite solar cells.

Defects formed at the surface, buried interface and grain boundaries (GB) of CsPbI3 perovskite films considerably limit photovoltaic performance. Such defects could be passivated effectively by the most prevalent post modification strategy without compromising the photoelectric properties of perovskite films, but it is still a great challenge to make this strategy comprehensive to different defects spatially distributed throughout the films. Herein, a spatially selective defect management (SSDM) strategy is developed to roundly passivate various defects at different locations within the perovskite film by a facile one-step treatment procedure using a piperazine-1,4-diium tetrafluoroborate (PZD(BF4)2) solution. The small-size PZD2+ cations could penetrate into the film interior and even make it all the way to the buried interface of CsPbI3 perovskite films, while the BF4- anions, with largely different properties from I- anions, mainly anchor on the film surface. Consequently, virtually all the defects at the surface, buried interface and grain boundaries of CsPbI3 perovskite films are effectively healed, leading to significantly improved film quality, enhanced phase stability, optimized energy level alignment and promoted carrier transport. With these films, the fabricated CsPbI3 PSCs based on carbon electrode (C-PSCs) achieve an efficiency of 18.27%, which is among the highest-reported values for inorganic C-PSCs, and stability of 500 h at 85 °C with 65% efficiency maintenance.

Regionalizing Nitrogen Doping of Polysilicon Films Enabling High-Efficiency Tunnel Oxide Passivating Contact Silicon Solar Cells.

Tunnel oxide passivating contact (TOPCon) solar cells (SCs) as one of the most competitive crystalline silicon (c-Si) technologies for the TW-scaled photovoltaic (PV) market require higher passivation performance to further improve their device efficiencies. Here, the successful construction of a double-layered polycrystalline silicon (poly-Si) TOPCon structure is reported using an in situ nitrogen (N)-doped poly-Si covered by a normal poly-Si, which achieves excellent passivation and contact properties simultaneously. The new design exhibits the highest implied open-circuit voltage of 755 mV and the lowest single-sided recombination current density (J0 ) of ≈0.7 fA cm⁻2 for a TOPCon structure and a low contact resistivity of less than 5 mΩ·cm2 , resulting in a high selectivity factor of ≈16. The mechanisms of passivation improvement are disclosed, which suggest that the introduction of N atoms into poly-Si restrains H overflow by forming stronger Si-N and N-H bonds, reduces interfacial defects, and induces favorable energy bending. Proof-of-concept TOPCon SCs with such a design receive a remarkable certified efficiency of 25.53%.

Long-Chain Gemini Surfactant-Assisted Blade Coating Enables Large-Area Carbon-Based Perovskite Solar Modules with Record Performance.

Carbon-based perovskite solar cells show great potential owing to their low-cost production and superior stability in ambient air. However, scaling up to high-efficiency carbon-based solar modules hinges on reliable deposition of uniform defect-free perovskite films over large areas, which is an unsettled but urgent issue. In this work, a long-chain gemini surfactant is introduced into perovskite precursor ink to enforce self-assembly into a network structure, considerably enhancing the coverage and smoothness of the perovskite films. The long gemini surfactant plays a distinctively synergistic role in perovskite film construction, crystallization kinetics modulation and defect passivation, leading to a certified record power conversion efficiency of 15.46% with Voc of 1.13 V and Jsc of 22.92 mA cm-2 for this type of modules. Importantly, all of the functional layers of the module are printed through a simple and high-speed (300 cm min-1) blade coating strategy in ambient atmosphere. These results mark a significant step toward the commercialization of all-printable carbon-based perovskite solar modules.

Fe(III) Docking-Activated Sites in Layered Birnessite for Efficient Water Oxidation.

Non-noble metal catalysts for promoting the sluggish kinetics of oxygen evolution reaction (OER) are essential to efficient water splitting for sustainable hydrogen production. Birnessite has a local atomic structure similar to that of an oxygen-evolving complex in photosystem II, while the catalytic activity of birnessite is far from satisfactory. Herein, we report a novel Fe-Birnessite (Fe-Bir) catalyst obtained by controlled Fe(III) intercalation- and docking-induced layer reconstruction. The reconstruction dramatically lowers the OER overpotential to 240 mV at 10 mA/cm2 and the Tafel slope to 33 mV/dec, making Fe-Bir the best of all the reported Bir-based catalysts, even on par with the best transition-metal-based OER catalysts. Experimental characterizations and molecular dynamics simulations elucidate that the catalyst features active Fe(III)-O-Mn(III) centers interfaced with ordered water molecules between neighboring layers, which lower reorganization energy and accelerate electron transfer. DFT calculations and kinetic measurements show non-concerted PCET steps conforming to a new OER mechanism, wherein the neighboring Fe(III) and Mn(III) synergistically co-adsorb OH* and O* intermediates with a substantially reduced O-O coupling activation energy. This work highlights the importance of elaborately engineering the confined interlayer environment of birnessite and more generally, layered materials, for efficient energy conversion catalysis.

Visualizing Interfacial Energy Offset and Defects in Efficient 2D/3D Heterojunction Perovskite Solar Cells and Modules.

Currently, the full potential of perovskite solar cells (PSCs) is limited by chargecarrier recombination owing to imperfect passivation methods. Here, the recombination loss mechanisms owing to the interfacial energy offset and defects are quantified. The results show that a favorable energy offset can reduce minority carriers and suppress interfacial recombination losses more effectively than chemical passivation. To obtain high-efficiency PSCs, 2D perovskites are promising candidates, which offer powerful field effects and require only modest chemical passivation at the interface. The enhanced passivation and charge-carrier extraction offered by the 2D/3D heterojunction PSCs has boosted their power conversion efficiency to 25.32% (certified 25.04%) for small-size devices and to 21.48% for a large-area module (with a designated area of 29.0 cm2 ). Ion migration is also suppressed by the 2D/3D heterojunction, such that the unencapsulated small-size devices maintain 90% of their initial efficiency after 2000 h of continuous operation at the maximum power point.

De Novo Studies of Working Mechanisms for Self-Driven Narrowband Perovskite Photodetectors.

Self-driven narrowband perovskite photodetectors have recently attracted significant attention due to their simple preparation, high performance, and amenability for system integration. However, the origin of narrowband photoresponse and the related regulation mechanisms still remains elusive. To address these issues, we herein perform a systematic investigation by formulating an analytic model in conjunction with finite element simulation. The optical and electrical simulations have resulted in design principles for perovskite narrowband photodetectors in terms of the dependence of external quantum efficiency (EQE) on perovskite layer thickness, doping concentration, and band gap as well as trap state concentration. Careful investigations on the profiles of electric field, current, and optical absorption reveal the dependence of narrowband EQE on the direction of incident light and perovskite doping types: only p-type perovskite can yield the narrowband photoresponse for illumination from the hole transport layer (HTL) side. The simulation results demonstrated in this study shed new light on the mechanism of perovskite-based narrowband photodetectors and provide valuable guidance for their design.

Interspace and Vacancy Modulation: Promoting the Zinc Storage of an Alcohol-Based Organic-Inorganic Cathode in a Water-Organic Electrolyte.

Expanding interspace and introducing vacancies are desired to promote the mobility of Zn ions and unlock the inactive sites of layered cathodes. However, this two-point modulation has not yet been achieved simultaneously in vanadium phosphate. Here, a strategy is proposed for fabricating an alcohol-based organic-inorganic hybrid material, VO1- x PO4 ·0.56C6 H14 O4 , to realize the conjoint modulation of the d-interspace and oxygen vacancies. Peculiar triglycol molecules with an inclined orientation in the interlayer also boost the improvement in the conversion rate of V5+ to V4+ and the intensity of the PO bond. Their synergism can ensure steerable adjustment for intercalation kinetics and electron transport, as well as realize high chemical reactivity and redox-center optimization, leading to at least 200% increase in capacity. Using a water-organic electrolyte, the designed Zn-ion batteries with an ultrahigh-rate profile deliver a long-term durability (fivefold greater than pristine material) and an excellent energy density of ≈142 Wh kg-1 (including masses of cathode and anode), thereby substantially outstripping most of the recently reported state-of-the-art zinc-ion batteries. This work proves the feasibility to realize the two-point modulation by using organic intercalants for exploiting high-performance new 2D materials.

A Heat-Liquefiable Solid Precursor for Ambient Growth of Perovskites with High Tunability, Performance and Stability.

Halide perovskites are intensively studied for applications in optoelectronic devices because of their outstanding properties and relatively low cost. However, the common precursor solutions for perovskite fabrication are rather unstable in the presence of moisture and oxygen, limiting the large-scale low-cost production of perovskite. Herein, water is used counterintuitively to formulate an ambient stable perovskite precursor, which is peculiar in that it is solid at room temperature but becomes a liquid at 75 °C. The non-fluidity of the precursor stemmed from the water-assisted intermediate fiber assembly, conferring high damp air stability. Yet the heat-liquefiability made the precursor highly processible for perovskite growth, and when guided by polyvinyl pyrrolidone coordination with Pb2+ , the perovskite can preferentially grow along the [200] direction, significantly improving the film quality. To demonstrate the utility of the precursor, it has been used to fabricate self-driven halide perovskite photodetectors, which exhibited a low noise current of 2.0 × 10-14  A Hz-1/2 , a high specific detectivity up to 1.4 × 1013 Jones, and high stability of 20 days of operation with only < 5% external quantum efficiency decay. This type of solid-liquid convertible precursor opens up new opportunities for wider applications of perovskites.

New Extraction Technique of In-Gap Electronic-State Spectrum Based on Time-Resolved Charge Extraction.

The in-gap electronic state (trap state) is an important factor that determines the photovoltaic performance of solar cells. In this article, we put forward a new technique for extracting the density of trap state (DOST) distribution based on the time-resolved charge extraction (TRCE) experiment result. Based on strict derivation, we find that when the TRCE result is linear, the extracted DOST distribution is exponential type and vice versa. Compared to the approach given by Wang et al., the method introduced in this paper is more accurate and reliable. Compared to the approach based on the space charge-limited current (SCLC) experiment result, our method needs less computation.

Extraction technique of trap states based on transient photo-voltage measurement.

This article puts forward a technique for extracting the density of trap states (DOST) distribution based on the transient photo-voltage (TPV) measurement result. We prove that when the TPV result is linear, the DOST distribution is exponential type and vice versa. Compared to the approach based on the space charge limited current measurement, the method given in this paper has the advantage of requiring less calculation. The results obtained by our method provides a guidance for preparing less trap states solar cells.