Huotian Zhang

Although organic solar cells have surpassed 20% power conversion efficiency, a persistent trade-off between open-circuit voltage and fill factor (FF) prevents them from closing the gap with inorganic technologies. Here we investigate this trade-off across a wide range of devices and identify an FF limit arising from field-dependent free-charge generation. This limit becomes more severe as voltage losses are minimized, thereby imposing an open-circuit voltage–FF trade-off. To quantitatively describe this limit, we develop an analytical model for field-dependent charge generation, revealing that the underlying cause is the field-sensitive charge-transfer process between excitons and charge-transfer states. This sensitivity originates from the field-induced charge-transfer state energy variations, mainly caused by the Stark effect. Guided by this physics-based model, we highlight that a long exciton lifetime is one of the practical and effective methods to overcome the FF limit.

Some metal organic–inorganic complexes (MOICs) are known for their glass-forming ability. However, the composition range of glass-forming MOICs is rather limited as the mechanism of MOIC glass formation has not been well understood. Here, we uncover the structural factors controlling MOIC glass formation and thereby develop new MOIC glass formers. MOIC glass formation relies on the creation of a hydrogen-bonded structural network. By properly choosing metal centers, anions, and organic ligands of MOICs, a supramolecular structural network can be constructed, thereby allowing property modulation. Furthermore, MOIC systems with mixed crystals are generated by ligand-mixing and then vitrified by melt-quenching. The glass-transition temperature (Tg) of the derived glasses can be linearly tuned through the substitution of benzimidazole for imidazole. Interestingly, vitrification led to disordering of hydrogen-bonded networks in MOICs at short-, medium-, and long-range scales. This work enables the expansion of the composition range of MOIC glasses with various functionalities.

As the stability of organic solar cells improves, traditional long-duration testing methods cannot provide timely feedback, retarding optimization and hindering commercialization. Therefore, accurate degradation forecasting becomes a critical challenge, as the complex, nonlinear degradation kinetics of OPV devices complicate prediction. Here, we present a machine learning pipeline based on Class Symbolic Regression (CSR) that accurately extrapolates device degradation ~10× beyond the measured window, enabling day-scale stability decisions. Our workflow achieves 3-4% test error in quantitatively forecasting lifetime using the first 20 h for preliminary screening (200 h) and the first 100 h for long-term stability testing (1,000 h). This approach, validated across >40 donor–acceptor systems and >100 processing conditions, demonstrates generalization across key stability metrics. Additionally, the workflow is lightweight, requiring few resources and training, making it suitable for various OPV laboratories, thereby compressing OPV stability-testing protocols from month-scale to days. This work accelerates decision-making, enhances R&D throughput, and advances commercialization in the OPV industry.

The rational design of non-fullerene acceptors (NFAs) with both high crystallinity and photoluminescence quantum yield (PLQY) is of crucial importance for achieving high-efficiency and low-energy-loss organic solar cells (OSCs). However, increasing the crystallinity of an NFA tends to decrease its PLQY, which results in a high non-radiative energy loss in OSCs. Here we demonstrate that the crystallinity and PLQY of NFAs can be fine-tuned by asymmetrically adapting the branching position of alkyl chains on the thiophene unit of the L8-BO acceptor. It was found that L8-BO-C₄, with 2-butyloctyl on one side and 4-butyldecyl on the other side, can simultaneously achieve high crystallinity and PLQY. A high efficiency of 20.42% (certified as 20.1%) with an open-circuit voltage of 0.894 V and a fill factor of 81.6% is achieved for the single-junction OSC. This work reveals how important the strategy of shifting the alkyl chain branching position is in developing high-performance NFAs for efficient OSCs.

Typically, organic solar cells (OSCs) and photodetectors (OPDs) comprise an electron donating and accepting material to facilitate efficient charge carrier generation. This approach has proven successful in achieving high‐performance devices but has several drawbacks for upscaling and stability. This study presents a fully vacuum‐deposited single‐component OPD, employing the neat oligothiophene derivative DCV2‐5T in the photoactive layer. Free charge carriers are generated with an internal quantum efficiency of 20 % at zero bias. By optimizing the device structure, a very low dark current of 3.4 · 10 ⁻¹¹  A cm ⁻² at −0.1 V is achieved, comparable to the dark current of state‐of‐the‐art bulk heterojunction OPDs. This optimization results in specific detectivities of 1· 10 ¹³  Jones (based on noise measurements), accompanied by a fast photoresponse ( f _‐3dB = 200 kHz) and a broad linear dynamic range (> 150 dB). Ultrafast transient absorption spectroscopy unveils that charge carriers are already formed at very short time scales (< 1 ps). The surprisingly efficient bulk charge generation mechanism is attributed to a strong electronic coupling of the molecular exciton and charge transfer states. This work demonstrates the very high performance of single‐component OPDs and proves that this novel device design is a successful strategy for highly efficient, morphological stable and easily manufacturable devices.

The power conversion efficiency of ternary organic solar cells (TOSCs), consisting of one host binary blend and one guest component, remains limited by large voltage losses. The fundamental understanding of the open-circuit voltage (V_OC) in TOSCs is controversial, limiting rational design of the guest component. In this study, we systematically investigate how the guest component affects the radiative and non-radiative related parts of V_OC of a series of TOSCs using the detailed balanced principle. We highlight that the thermal population of charge-transfer and local exciton states provided by the guest binary blend (that is, the guest-component-based binary blend) has a significant influence on the non-radiative voltage losses. Ultimately, we provide two design rules for enhancing the V_OC in TOSCs: high emission yield for the guest binary blend and similar charge-transfer-state energies for host/guest binary blends; high miscibility of the guest component with the low gap component in the host binary blend.

Energy level alignment (ELA) at donor (D) -acceptor (A) heterojunctions is essential for understanding the charge generation and recombination process in organic photovoltaic devices. However, the ELA at the D-A interfaces is largely underdetermined, resulting in debates on the fundamental operating mechanisms of high-efficiency non-fullerene organic solar cells. Here, we systematically investigate ELA and its depth-dependent variation of a range of donor/non-fullerene-acceptor interfaces by fabricating and characterizing D-A quasi bilayers and planar bilayers. In contrast to previous assumptions, we observe significant vacuum level (VL) shifts existing at the D-A interfaces, which are demonstrated to be abrupt, extending over only 1–2 layers at the heterojunctions, and are attributed to interface dipoles induced by D-A electrostatic potential differences. The VL shifts result in reduced interfacial energetic offsets and increased charge transfer (CT) state energies which reconcile the conflicting observations of large energy level offsets inferred from neat films and large CT energies of donor - non-fullerene-acceptor systems.

Photovoltaics are one of the most important sustainable energy sources in the 21st century. Among photovoltaics, organic solar cells (OSCs) offer many advantages such as ease of processing, lightwe ...