On the Conformation of Dimeric Acceptors and Their Polymer Solar Cells with Efficiency over 18 %

The determination of molecular conformations of oligomeric acceptors (OAs) and their impact on molecular packing are crucial for understanding the photovoltaic performance of their resulting polymer solar cells (PSCs) but have not been well studied yet. Herein, we synthesized two dimeric acceptor materials, DIBP3F-Se and DIBP3F-S, which bridged two segments of Y6-derivatives by selenophene and thiophene, respectively. Theoretical simulation and experimental 1D and 2D NMR spectroscopic studies prove that both dimers exhibit O-shaped conformations other than S- or U-shaped counter-ones. Notably, this O-shaped conformation is likely governed by a distinctive “conformational lock” mechanism, arising from the intensified intramolecular π–π interactions among their two terminal groups within the dimers. PSCs based on DIBP3F-Se deliver a maximum efficiency of 18.09 %, outperforming DIBP3F-S-based cells (16.11 %) and ranking among the highest efficiencies for OA-based PSCs. This work demonstrates a facile method to obtain OA conformations and highlights the potential of dimeric acceptors for high-performance PSCs

28.2%-efficient, outdoor-stable perovskite/silicon tandem solar cell

Stacking perovskite solar cells onto crystalline silicon bottom cells in a monolithic tandem configuration enables power-conversion efficiencies (PCEs) well above those of their single-junction counterparts. However, state-of-the-art wide-band-gap perovskite films suffer from phase stability issues. Here, we show how carbazole as an additive to the perovskite precursor solution can not only reduce nonradiative recombination losses but, perhaps more importantly, also can suppress phase segregation under exposure to moisture and light illumination. This enables a stabilized PCE of 28.6% (independently certified at 28.2%) for a monolithic perovskite/silicon tandem solar cell over ∼1 cm2 and 27.1% over 3.8 cm2, built from a textured silicon heterojunction solar cell. The modified tandem devices retain ∼93% of their performance over 43 days in a hot and humid outdoor environment of almost 100% relative humidity over 250 h under continuous 1-sun illumination and about 87% during a 85/85 damp-heat test for 500 h, demonstrating the improved phase stability

Precise insertion of clickable monomer along polymer backbone by dynamic temperature controlled radical polymerization

Styrenic copolymers have been prepared that contain localized areas of high azide functionality by exploiting the unexpected copolymerization behavior of azidomethyl styrene with styrene. Kinetic studies have shown that during the nitroxide-mediated polymerization of styrene and azidomethyl styrene, small equivalents of azidomethyl styrene are consumed at a relatively higher rate. This property was further enhanced by lowering the reaction temperature, leading to a more precisely defined area of azide functionality. Furthermore, by actively controlling the reaction temperature azidomethyl styrene can be inserted into different points along the polymer backbone. This approach was used in combination with previous sequence control techniques, strong donor/acceptor comonomer pairs, to synthesize well-defined copolymers with controlled areas of functional monomers allowing for a wide scope of post-polymerization modification methods

Monolithic Perovskite-Perovskite-Organic Triple-Junction Solar Cells with a Voltage Output Exceeding 3 V

Monolithic integration of perovskite-perovskite-organic subcells yields a triple-junction solar cell with a record open-circuit voltage of 3.03 V and a power conversion efficiency of 19.4%. The proposed triple-junction architecture represents a milestone toward scalable photovoltaics, targeting efficiencies beyond the limit of single-junction devices.</p

Charge Carrier Recombination at Perovskite/Hole Transport Layer Interfaces Monitored by Time-Resolved Spectroscopy

Carrier recombination at the interface between charge extraction layers and the perovskite photoactive layer in solar cells reduces the quasi-Fermi level splitting (QFLS) and hence the device's open-circuit voltage (VOC). Distinguishing between interfacial carrier recombination and charge extraction requires selective probing of carrier dynamics with transient optical spectroscopy techniques. However, bulk recombination, interfacial recombination, and charge extraction all contribute to the transient response, making a precise determination of individual rates challenging. Here, we compare two commonly used hole transport layers (HTLs), namely, PTAA and NiOx, adjacent to prototypical MAPI3 perovskite photoactive layers and wide-bandgap perovskites. We demonstrate that combining time-resolved photoluminescence (TR-PL) and transient absorption (TA) spectroscopy measurements can reveal recombination losses associated with the perovskite/NiOx interface, as confirmed by drift-diffusion simulations. The best performing MAPI3/PTAA-based device exhibits less nonradiative recombination and more efficient charge extraction, facilitated by favorable energy level alignment

Efficient bifacial monolithic perovskite/silicon tandem solar cells via bandgap engineering

Bifacial monolithic perovskite/silicon tandem solar cells exploit albedo—the diffuse reflected light from the environment—to increase their performance above that of monofacial perovskite/silicon tandems. Here we report bifacial tandems with certified power conversion efficiencies &gt;25% under monofacial AM1.5G 1 sun illumination that reach power-generation densities as high as ~26 mW cm–2 under outdoor testing. We investigated the perovskite bandgap required to attain optimized current matching under a variety of realistic illumination and albedo conditions. We then compared the properties of these bifacial tandems exposed to different albedos and provide energy yield calculations for two locations with different environmental conditions. Finally, we present a comparison of outdoor test fields of monofacial and bifacial perovskite/silicon tandems to demonstrate the added value of tandem bifaciality for locations with albedos of practical relevance

Toward Stable Monolithic Perovskite/Silicon Tandem Photovoltaics: A Six-Month Outdoor Performance Study in a Hot and Humid Climate

Perovskite/silicon tandem solar cells are emerging as a high-efficiency and prospectively cost-effective solar technology with great promise for deployment at the utility scale. However, despite the remarkable performance progress reported lately, assuring sufficient device stability-particularly of the perovskite top cell-remains a challenge on the path to practical impact. In this work, we analyze the outdoor performance of encapsulated bifacial perovskite/silicon tandems, by carrying out field-testing in Saudi Arabia. Over a six month experiment, we find that the open circuit voltage retains its initial value, whereas the fill factor degrades, which is found to have two causes. A first degradation mechanism is linked with ion migration in the perovskite and is largely reversible overnight, though it does induce hysteretic behavior over time. A second, irreversible, mechanism is caused by corrosion of the silver metal top contact with the formation of silver iodide. These findings provide directions for the design of new and more stable perovskite/silicon tandem

Efficient tandem solar cells with solution-processed perovskite on textured crystalline silicon

This is the author’s version of the work. It is posted here by permission of the AAAS for personal use, not for redistribution. The definitive version was published in Science Volume 367 on April 6, 2020, DOI: 10.1126/science.aaz3691.Stacking solar cells with decreasing band gaps to form tandems presents the possibility of overcoming the single-junction Shockley-Queisser limit in photovoltaics. The rapid development of solution-processed perovskites has brought perovskite single-junction efficiencies >20%. However, this process has yet to enable monolithic integration with industry-relevant textured crystalline silicon solar cells. We report tandems that combine solution-processed micrometer-thick perovskite top cells with fully textured silicon heterojunction bottom cells. To overcome the charge-collection challenges in micrometer-thick perovskites, we enhanced threefold the depletion width at the bases of silicon pyramids. Moreover, by anchoring a self-limiting passivant (1-butanethiol) on the perovskite surfaces, we enhanced the diffusion length and further suppressed phase segregation. These combined enhancements enabled an independently certified power conversion efficiency of 25.7% for perovskite-silicon tandem solar cells. These devices exhibited negligible performance loss after a 400-hour thermal stability test at 85°C and also after 400 hours under maximum power point tracking at 40°C.This publication is based upon work supported by the King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under award no. OSR-2018-CPF-3669.02, KAUST OSR-CARF URF/1/3079-33-01, KAUST OSR-CRG URF/1/3383, and KAUST OSR-CRG2018-3737, and in part on work supported by the U.S. Department of the Navy, Office of Naval Research (grant award no. N00014-17-1-2524). This work was authored in part by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under contract no. DE-AC36-08GO28308 (De-risking Halide Perovskite Solar Cells program of the National Center for Photovoltaics, funded by the DOE Office of Energy Efficiency and Renewable Energy, Solar Energy Technologies Office). This work has been partially supported by NSF MRI (1428992), the U.S.-Egypt Science and Technology (S&T) Joint Fund, and the EDA University Center Program (ED18DEN3030025)