Chen Weijie

Herein, the doping effect on semiconductor oxide‐based electron transport materials, especially for the typical TiO₂, in perovskite solar cells is reviewed and emphasized by classifying the doping ions according to the main family of elements from the critical factors of lattice optimization, carrier transporting improvement, and interface modification.

From the perspective of the device structure of perovskite solar cells (PSCs), the electron transport layer is one of the essential components and plays a significant role in suppressing carrier recombination. Furthermore, its decisiveness is related to the quality of perovskite film, the rapid interface carrier extraction, and the bandgap alignment. However, the deficiency of the semiconductor oxides based electron transport materials, especially for most studied TiO₂, is that their carrier mobility is one to three orders of magnitude lower than the most commonly used hole transport materials, leading to an imbalanced carrier flux and unpredicted hysteresis. Doping new ions are the most effective ways to improve electron mobility and tune the bandgap, while the fundamental mechanism of doping in the majority of cases are still lacking. Herein, the doping effect on semiconductor oxides is reviewed and emphasized by classifying the doping ions according to the critical factors of lattice optimization, a carrier transporting improvement, and interface modification. This review is the first systematic summary of the ion doping characteristics in oxide electron transport layers of PSCs. Finally, the implementation of doping ions in electron transport materials is briefly discussed for further enhancing the photovoltaic performance of PSCs.

Recent advances in organic photovoltaic (OPV) materials and processing technologies are promising for transitioning of OPV devices from laboratory‐scale to large‐area industrial scale modules. Recent breakthroughs attained by development of nonfullerene acceptors have led to significant enhancement in power conversion efficiency. It is essential to elucidate degradation mechanisms of OPV devices for improving device long‐term stability.

Abstract

Organic solar cells based on bulk heterojunctions (BHJs) are attractive energy‐conversion devices that can generate electricity from absorbed sunlight by dissociating excitons and collecting charge carriers. Recent breakthroughs attained by development of nonfullerene acceptors result in significant enhancement in power conversion efficiency (PCEs) exceeding 17%. However, most of researches have focused on pursuing high efficiency of small‐area (<1 cm²) unit cells fabricated usually with spin coating. For practical application of organic photovoltaics (OPVs) from lab‐scale unit cells to industrial products, it is essential to develop efficient technologies that can extend active area of devices with minimized loss of performance and ensured operational stability. In this progress report, an overview of recent advancements in materials and processing technologies is provided for transitioning from small‐area laboratory‐scale devices to large‐area industrial scale modules. First, development of materials that satisfy requirements of high tolerability in active layer thickness and large‐area adaptability is introduced. Second, morphology control using various coating techniques in a large active area is discussed. Third, the recent research progress is also underlined for understanding mechanisms of OPV degradation and studies for improving device long‐term stability along with reliable evaluation procedures.

The moisture instability and unscalable fabrication protocols are still unsolved and blocking FACs‐based perovskite solar cells’ further applications. Here, high‐quality FACsPbI₃ films are fabricated by crown ether tailoring (which chelated with Cs⁺/Pb²⁺ ions) to inhibit the moisture invasion and stabilize the α‐phase FACsPbI₃, producing large‐area perovskite films and improving solar module performance.

Abstract

FACs‐based (FA⁺, formamidinium and Cs⁺, cesium) perovskite solar cells have gained great attention due to their remarkable light and thermal stabilities toward practical application of perovskite modules. However, the moisture instability and difficulty in scalable fabrication are still the main obstacles blocking their photovoltaic applications in current status. Here, the employment of novel interaction between crown ether with metal cations is introduced to tailor the uniform growth and inhibit moisture invasion during the crystallization of α‐phase FACsPbI₃, yielding the successful synthesis of high‐quality perovskite films in a large scale. Consequently, perovskite solar cells (PSC) modules in the total area of 4 × 4 and 10 × 10 cm² are readily fabricated with respective champion efficiencies of 16.69% and 13.84% and excellent stability over 1000 h. This facile scaling‐up strategy assisted by crown ether has shown great promise for pursuing efficient and highly stable large‐area PSC modules.

A new class of polymer acceptors (P _As, P(BDT2BOY5‐X)) consisting of benzodithiophene (BDT) and non‐fullerene small molecule‐accepting units is developed, which shows excellent material compatibility with an efficient BDT‐based polymer donor (P _D). The resulting all‐polymer solar cells show excellent photovoltaic efficiency, thermal stability, and mechanical robustness at the same time, benefitting from the high chemical and molecular compatibilities between P _D and P _A.

Abstract

All‐polymer solar cells (all‐PSCs) are a highly attractive class of photovoltaics for wearable and portable electronics due to their excellent morphological and mechanical stabilities. Recently, new types of polymer acceptors (P _As) consisting of non‐fullerene small molecule acceptors (NFSMAs) with strong light absorption have been proposed to enhance the power conversion efficiency (PCE) of all‐PSCs. However, polymerization of NFSMAs often reduces entropy of mixing in PSC blends and prevents the formation of intermixed blend domains required for efficient charge generation and morphological stability. One approach to increase compatibility in these systems is to design P _As that contain the same building blocks as their polymer donor (P _D) counterparts. Here, a series of NFSMA‐based P _As [P(BDT2BOY5‐X), (X = H, F, Cl)] are reported, by copolymerizing NFSMA (Y5‐2BO) with benzodithiophene (BDT), a common donating unit in high‐performance P _Ds such as PBDB‐T. All‐PSC blends composed of PBDB‐T P _D and P(BDT2BOY5‐X) P _A show enhanced molecular compatibility, resulting in excellent morphological and electronic properties. Specifically, PBDB‐T:P(BDT2BOY5‐Cl) all‐PSC has a PCE of 11.12%, which is significantly higher than previous PBDB‐T:Y5‐2BO (7.02%) and PBDB‐T:P(NDI2OD‐T2) (6.00%) PSCs. Additionally, the increased compatibility of these all‐PSCs greatly improves their thermal stability and mechanical robustness. For example, the crack onset strain (COS) and toughness of the PBDB‐T:P(BDT2BOY5‐Cl) blend are 15.9% and 3.24 MJ m^–3, respectively, in comparison to the PBDB‐T:Y5‐2BO blends at 2.21% and 0.32 MJ m^–3.

Bridge‐jointed 2D nanosheets are inserted between the methylammonium‐free perovskite and the dopant‐free hole transport layer (HTL) to form a scalable heterostructure, which preserves p‐type semiconduction of HTL and suppresses nonradiative‐recombination. Further, a perovskite solar module with an area of 35.80 cm² shows a certified efficiency of 15.3% and encapsulated modules retain over 91% of initial efficiency after damp heat test for 1000 h.

Abstract

Perovskite solar cell (PSC) modules employing a hole transport layer (HTL) without unstable dopants possess high potential for improving operational stability. However, the low efficiencies of the devices greatly limit their commercial applications owing to the lower efficacy of the dopant‐free HTL, introduced by the unintentional n‐doping effect of volatile ions from the halide‐rich perovskite surface. Here, a scalable heterostructure integrated by a methylammonium‐free perovskite film with an iodide‐rich surface, an ultrathin interlayer of bridge‐jointed graphene oxide nanosheets (BJ‐GO), and an HTL without additional ionic dopants is developed. In this heterostructure, the iodide ions are physically immobilized by the compact 2D network, and lead defects are chemically passivated by multiple coordination bonds. Moreover, the BJ‐GO with tunable surface energy enables a highly ordered HTL a considerably improved carrier mobility by an order of magnitude. Finally, the PSC module with an area of 35.80 cm² employing this heterostructure shows a certified efficiency of 15.3%. The encapsulated PSC modules retain over 91% of initial efficiency after the damp heat test at 85 °C and ≈85% relative humidity for 1000 h, while maintaining 90% of the initial value for 1000 h at the maximum power point under continuous 1‐Sun illumination at 60 °C.

Publication date: April 2021

Source: Nano Energy, Volume 82

Author(s): Boer Tan, Sonia R. Raga, Kevin James Rietwyk, Jianfeng Lu, Sebastian O. Fürer, James C. Griffith, Yi-Bing Cheng, Udo Bach

Publication date: April 2021

Source: Nano Energy, Volume 82

Author(s): Claudia Caddeo, Alessio Filippetti, Andrea Bosin, Christine Videlot-Ackermann, Jörg Ackermann, Alessandro Mattoni

Publication date: April 2021

Source: Nano Energy, Volume 82

Author(s): Narges Yaghoobi Nia, Mahmoud Zendehdel, Mojtaba Abdi-Jalebi, Luigi Angelo Castriotta, Felix U. Kosasih, Enrico Lamanna, Mohammad Mahdi Abolhasani, Zhaoxiang Zheng, Zahra Andaji-Garmaroudi, Kamal Asadi, Giorgio Divitini, Caterina Ducati, Richard H. Friend, Aldo Di Carlo

Publication date: April 2021

Source: Nano Energy, Volume 82

Author(s): Xinyu Yu, Zhen Li, Xianglang Sun, Cheng Zhong, Zonglong Zhu, Zhong’an Li, Alex K.-Y. Jen

Herein, excitation wavelength‐dependent charge generation dynamics in nonfullerene solar cells is revealed by time‐dependent density functional theory (TDDFT)‐based nonadiabatic dynamics simulations.

Unraveling the charge generation dynamics at the donor–acceptor (D−A) interfaces is crucial for improving the photovoltaic performances of nonfullerene acceptor‐based organic solar cells (OSCs). Herein, time‐dependent density functional theory (TDDFT) based nonadiabatic dynamics simulations are used to explore the ultrafast photoinduced dynamics at a nonfullerene D–A PTB7@PDI interface. Based on the results, it is found that such an interface exhibits distinct charge generation processes upon excitation with different wavelengths. The excitation at ≈591 nm mainly results in the local exciton |PTB7 ^∗ >, whereas the charge transfer exciton |PTB7 ⁺ PDI ⁻ > also has minor contribution. Later on, the electron transfer from PTB7 to PDI, i.e., channel I charge generation process, occurs in 1 ps. The situations are much more complex when the excitation is conducted using ≈487 nm light. The initial populated excitons include local excitons |PDI ^∗ >, |PTB7 ^∗ >, and charge transfer exciton |PTB7 ⁺ PDI ⁻ >, after which both channel I and channel II charge generation take place ultrafast. However, in both situations, the charge generation processes occur within a few picoseconds, which is consistent with previous experimental work. Such ultrafast charge generation processes in a wide range of solar spectra are one of the reasons responsible for the excellent photovoltaic properties of such OSCs.

Herein, advances in solar photovoltaic technologies for building integration are reviewed, with focus on transparent photovoltaics and colored photovoltaics. Theoretical analysis and technical routes concerning materials and device structures are highlighted for analyzing different methods. Finally, perspectives are presented to provide suggestions for further improving the performance of aesthetic building‐integrated photovoltaics.

Building‐integrated photovoltaics (BIPVs) stand as a promising solution to provide renewable electricity for achieving zero‐energy buildings, although still hindered from large‐scale implementations due to the difficulty of traditional photovoltaic modules in meeting the standards and aesthetics of architectural materials. The emergence of new photovoltaic materials and devices could pave the way for the future through offering diversity and tunability in colors and transparency along with comparable performance. Herein the recent advances in BIPVs are discussed, starting from an overview of various photovoltaic technologies regarding their material characteristics, state of the art, and adaptability to the built environment. The transparent and colored photovoltaic technologies are then respectively emphasized, concerning design principles, theoretical analysis, technical routes, and corresponding demonstration studies. The various strategies, including the materials and structures adopted to modify the transparency and color of solar cells, are highlighted. Finally, the challenges and future perspectives are addressed, followed by an outlook on factors that are critical for large‐scale implementation of BIPVs in the future.

The power conversion efficiencies (PCEs) of single‐junction organic solar cells have now reached over 18%. Recent progress that has been made in understanding the morphology and the device photophysics of high performing polymer:non‐fullerene acceptor blends and some of the major challenges that must be overcome to attain PCEs of over 20% are highlighted.

Abstract

The power conversion efficiencies (PCEs) of single‐junction organic solar cells (OSC) have now reached over 18%. This rapid recent progress can be attributed to the development of new nonfullerene electron acceptors (NFAs) that are paired with suitable high performing polymer electron donors. Substantial improvements in the PCEs and long‐term stability enabled by NFA OSCs have allowed the development and integration of these systems into many niche and novel applications. Here, the recent progress that has been made in understanding the device photophysics of high performing polymer:NFA blends is highlighted. As the bulk heterojunction morphology is intrinsically linked to the device photophysics, this review focuses on studies that have provided noteworthy morphological insights using advanced techniques such as solid‐state NMR and resonant soft X‐ray scattering. Through this, some of the major challenges that must be overcome to attain PCEs of over 20% in NFA OSCs are addressed.

Conformation effects of Y6‐type acceptors are systematically studied based on asymmetric design strategies. Z‐shape and W‐shape conformations‐based acceptors can help reduce energy loss in devices through significantly suppressed nonradiative energy loss. Benefiting from the high open‐circuit voltage of BP5T‐4F in the devices, ternary organic solar cells based on PM6:BP5T‐4F:CH1007 achieve a 17.2% efficiency.

Abstract

Y6, as a state‐of‐the‐art nonfullerene acceptor (NFA), is extensively optimized by modifying its side chains and terminal groups. However, the conformation effects on molecular properties and photovoltaic performance of Y6 and its derivatives have not yet been systematically studied. Herein, three Y6 analogs, namely, BP4T‐4F, BP5T‐4F, and ABP4T‐4F, are designed and synthesized. Owing to the asymmetric molecular design strategies, three representative molecular conformations for Y6‐type NFAs are obtained through regulating the lateral thiophene orientation of the fused core. It is found that conformation adjustment imposes comprehensive effects on the molecular properties in neat and blend films of these NFAs. As a result, organic solar cells (OSCs) fabricated with PM6:BP4T‐4F, PM6:BP5T‐4F, and PM6:ABP4T‐4F show high power conversion efficiency of 17.1%, 16.7%, and 15.2%, respectively. Interestingly, these NFAs with different conformations also show reduced energy loss (E _loss) in devices via gradually suppressed nonradiative E _loss. Moreover, by employing a selenium‐containing analog, CH1007, as the complementary third component, ternary OSCs based on PM6:BP5T‐4F:CH1007 (1:1.02:0.18) achieve a 17.2% efficiency. This work helps shed light on engineering the molecular conformation of NFAs to achieve high efficiency OSCs with reduced voltage loss.

High‐quality and all‐inorganic CsPbI₂Br perovskite film with lower defects and improved hydrophobicity is prepared via a facile additive engineering with trace S₈, resulting in inverted solar cells with improved efficiency and stability.

Though prized for excellent thermal stability, inorganic perovskites are still behind organic/inorganic hybrid perovskites due to their high‐density defects and poor hydrophobicity. Herein, trace hydrophobic S₈ is used as additive to optimize the solution‐processed CsPbI₂Br perovskite film. A series of characterizations reveal that S₈ additive not only leads to retarded crystallization of α‐CsPbI₂Br perovskite at low temperature (<150 °C) via self‐formed Pb(S₈) _x ²⁺ intermediate but also induces efficient grain‐boundary passivation via distinctive PbS coordination interaction and reduced wettability on perovskite surface, which all point to the formation of the perovskite film with reduced defects and improved hydrophobicity. As a result, the inverted perovskite solar cells (PSCs) based on the optimized all‐inorganic perovskite of CsPbI₂Br:S₈ deliver an increased power conversion efficiency (PCE) from 12.76% to 14.46% as well as remarkably enhanced device stability under thermal or ambient condition. This work thus provides a simple way as well as new insights for boosting the performance of solution‐processed all‐inorganic perovskite.

In the structure of perovskite solar cells, N‐type semiconductor AgBiS₂ and dimethyl sulfoxide solvent mixed polyethylene glycol are used for perovskite film treatment. Finally, the perovskite solar cells with dual‐interfacial modification exhibite a remarkable improvement of power conversion efficiency from 18.58% to 21.19%, as well as show the excellent long‐term and moisture stability.

Although the research on perovskite solar cells (PSCs) has achieved rapid progress, its efficiency and stability still need to be further improved to meet the industrial requirements. The defects located inside the cells, on the surfaces, interfaces, or grain boundaries, will primarily affect carrier transportation through the formation of nonradiative recombination centers and hinder the further enhancement of the power conversion efficiency (PCE). Herein, a straightforward and simple defect passivation method is developed to increase the PCE and stability of PSCs. In the device, the N‐type semiconductor AgBiS₂ is introduced by thermal evaporation as a modified layer between the perovskite films and electron transport layer, which can improve the charge transport characteristic and bandgap optimization of PSCs. Simultaneously, dimethyl sulfoxide (DMSO) solvent mixed polyethylene glycol (PEG) is used for solvent annealing treatment, which can further improve the quality of perovskite film and reduce the trap density by increasing grain size and enhancing the crystallinity. As a result, the PSCs with dual‐interfacial modification exhibit a remarkable improvement in PCE from 18.58% to 21.19% with exceptional long‐term and moisture stability. This work provides an innovative insight for fabricating the stable and efficient PSCs toward the industrialization.