The ternary strategy has been widely identified as an effective approach to obtain high‐efficiency organic solar cells (OSCs). However, for most ternary OSCs, the nonradiative voltage loss lies between those of the two binary devices, which limits further efficiency improvements. Herein, an asymmetric guest acceptor BTP‐2F2Cl is designed and incorporated into a PM1:L8‐BO host blend. Compared with the L8‐BO neat film, the L8‐BO:BTP‐2F2Cl blend film shows higher photoluminescence quantum yield and larger exciton diffusion length. Introducing BTP‐2F2Cl into the host blend extends its absorption spectrum, improves the molecular packing of host materials, and suppresses the nonradiative charge recombination of the ternary OSCs. Consequently, the power conversion efficiency is improved up to 19.17% (certified value 18.7%), which represents the highest efficiency value reported for single‐junction OSCs so far. The results show that improving the exciton behaviors is a promising approach to reducing the nonradiative voltage loss and realizing high‐performance OSCs.

Single‐Junction Organic Solar Cells with 19.17% Efficiency Enabled by Introducing One Asymmetric Guest Acceptor

Symmetric conjugated molecules can be broken through suitable synthetic strategies to construct novel asymmetric molecules, which can largely broaden the material library. In the field of organic solar cells, fused‐ring electron acceptors (FREAs) with the A‐DA'D‐A type backbone structure have attracted much attention and enabled power conversion efficiencies (PCE) exceeding 18%. Among them, Y6 is one of the most classic FREAs that can derive many symmetric and asymmetric molecules and exhibit unique optoelectronic properties. Thus, in this review, the focus is on the recent progress of Y6‐derived asymmetric FREAs containing a dipyrrolobenzothiadiazole segment, which can be classified as the following three categories: asymmetric end group, asymmetric central core and asymmetric side chain. The relationship of the molecular structure, optoelectronic properties, and device performance is discussed in detail. Finally, the future design directions and challenges faced by this kind of photovoltaic materials are given.

Recent Progress of Y6‐Derived Asymmetric Fused Ring Electron Acceptors

Following the 2nd release of the “Emerging PV reports,” the best achievements in the performance of emerging photovoltaic devices in diverse emerging photovoltaic research subjects are summarized, as reported in peer‐reviewed articles in academic journals since August 2021. Updated graphs, tables, and analyses are provided with several performance parameters, e.g., power conversion efficiency, open‐circuit voltage, short‐circuit current density, fill factor, light utilization efficiency, and stability test energy yield. These parameters are presented as a function of the photovoltaic bandgap energy and the average visible transmittance for each technology and application, and are put into perspective using, e.g., the detailed balance efficiency limit. The 3rd installment of the “Emerging PV reports” extends the scope toward triple junction solar cells.

Device Performance of Emerging Photovoltaic Materials (Version 3)

Blends of polymer donors (PDs) and small molecule acceptors (SMAs) have afforded highly efficient polymer solar cells (PSCs). However, most of the efficient PSCs are processed using toxic halogenated solvents, and they are mechanically fragile. Here, a new series of PDs by incorporating a hydrophilic oligo(ethylene glycol) flexible spacer (OEG‐FS) is developed, and efficient PSCs with a high power conversion efficiency (PCE) of 17.74% processed by a non‐halogenated solvent are demonstrated. Importantly, the incorporation of these OEG‐FSs into the PDs significantly increases the mechanical robustness and ductility of resulting PSCs, making them suitable for application as stretchable devices. The OEG‐FS alleviates excessive backbone rigidity of the PDs while enhancing their pre‐aggregation in the non‐halogenated solvent. In addition, the OEG‐FS in the PDs enhances PD‐SMA interfacial interactions and improves blend morphology, resulting in efficient charge generation and mechanical stress dissipation. The resulting PSCs demonstrate a superior PCE (17.74%) and high crack‐onset strain (COS = 10.50%), outperforming the PSCs without OEG (PCE = 15.64% and COS = 2.99%). Importantly, intrinsically stretchable (IS) PSCs containing the PD featuring OEG‐FS exhibit a high PCE (12.05%) and stretchability (maintaining 80% of the initial PCE after 22% strain), demonstrating their viability for wearable applications.

Intrinsically Stretchable and Non‐Halogenated Solvent Processed Polymer Solar Cells Enabled by Hydrophilic Spacer‐Incorporated Polymers

Modulating the molecular orientation of linear benzodifuran-based isomeric polymers by exchanging the positions of chlorine and fluorine atoms

Ternary strategy has been identified as a feasible and effective way to obtain high-efficiency organic solar cells (OSCs). However, for most ternary OSCs, the voltage loss (Vloss) lies between those...

Ternary Strategy Enabling High-Efficiency Rigid and Flexible Organic Solar Cells with Reduced Non-radiative Voltage Loss

Molecular design of polymer donors is of vital importance for obtaining high‐performance organic solar cells (OSCs). At present, much of the important progress in power conversion efficiencies (PCEs) achieved for OSCs has been associated with the benzodithiophene (BDT)‐based polymers, while the highest PCE of benzo[1,2‐b:4,5‐b′]difuran (BDF) polymer‐based OSCs only reaches 14.0%. Here, a polymer donor named PBDF‐NS is designed and synthesized by using naphthalene‐substituted benzo[1,2‐b:4,5‐b′]difuran as the electron‐sufficient units and fluorinated benzotriazole (BTz) as the electron‐deficient units. PBDF‐NS possesses a low‐lying HOMO level of −5.44 eV and a wide bandgap of 1.87 eV. When using LC301 as the acceptor, PBDF‐NS‐based OSC exhibits an excellent PCE of 15.24%. Moreover, the ternary and all‐polymer devices based on PBDF‐NS both achieve a higher PCE over 16%, which represents the highest efficiency values reported for BDF polymer‐based OSCs in the literature thus far. Meanwhile, the binary and ternary devices all display excellent storage and light‐soaking stabilities. The results demonstrate that by rational molecular design, BDF‐based copolymers can be comparable to or even surpass the performance of BDT‐based counterparts and also show great potential for realizing high‐efficiency all‐polymer solar cells.

Benzo[1,2‐b:4,5‐b′]difuran Based Polymer Donor for High‐Efficiency (>16%) and Stable Organic Solar Cells

Recent progress of nanotechnology in enhancing hydrogen storage performance of magnesium-based materials: A review

At present, a variety of benzo[1,2‐b:4,5‐b′]dithiophene (BDT)‐based polymer donors are designed and synthesized, which have made great progress toward achieving high power conversion efficiencies (PCEs) of polymer solar cells (PSCs). Despite many advantages of benzo[1,2‐b:4,5‐b′]difuran (BDF) compared with BDT unit, the overall performance of BDF polymer‐based PSCs lags far behind that of the counterpart BDT‐based polymers. Recently, great advances have been achieved in BDF polymer‐based PSCs with the highest PCEs over 16%, suggesting that BDF‐based polymers have the significant potential to catch up or even surpass the performance of BDT‐based polymers. In this review, the recent advances of BDF polymers in PSCs are first summarized and then the design strategies and the chemical structure–performance relationships of BDF polymers are discussed. Finally, perspectives on the future development of BDF polymers for high‐efficiency PSCs are provided.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/smsc.202200006

Xiaoming Li

Papers

Ternary Strategy Enabling High-Efficiency Rigid and Flexible Organic Solar Cells with Reduced Non-radiative Voltage Loss

Benzo[1,2‐b:4,5‐b′]difuran Based Polymer Donor for High‐Efficiency (>16%) and Stable Organic Solar Cells

Recent progress of nanotechnology in enhancing hydrogen storage performance of magnesium-based materials: A review

Recent Progress of Benzodifuran‐Based Polymer Donors for High‐Performance Organic Photovoltaics

Effects of ball milling time on the microstructure and hydrogen storage performances of Ti21.7Y0.3Fe16Mn3Cr alloy