Organic solar cells (OSCs) based on nonfullerene acceptors (NFAs) have made significant breakthrough in their device performance, now achieving a power conversion efficiency of ≈18% for single junction devices, driven by the rapid development in their molecular design and device engineering in recent years. However, achieving long‐term stability remains a major challenge to overcome for their commercialization, due in large part to the current lack of understanding of their degradation mechanisms as well as the design rules for enhancing their stability. In this review, the recent progress in understanding the degradation mechanisms and enhancing the stability of high performance NFA‐based OSCs is a specific focus. First, an overview of the recent advances in the molecular design and device engineering of several classes of high performance NFA‐based OSCs for various targeted applications is provided, before presenting a critical review of the different degradation mechanisms identified through photochemical‐, photo‐, and morphological degradation pathways. Potential strategies to address these degradation mechanisms for further stability enhancement, from molecular design, interfacial engineering, and morphology control perspectives, are also discussed. Finally, an outlook is given highlighting the remaining key challenges toward achieving the long‐term stability of NFA‐OSCs.

Organic solar cells (OSCs) are an alternative photovoltaic technology with a promising potential for a cost-effective, clean and sustainable source of energy. The performance of the solution-processable fullerene-based OSCs has been extensively investigated. However, the weak absorption in the long wavelength range, limited electronic property tuning capability and expensive purification processes are some of the limiting fac-Remarkable progress has been made in the development of high-efficiency solution-processable nonfullerene organic solar cells (OSCs). However, the effect of the vertical stratification of bulk heterojunction (BHJ) on the efficiency and stability of nonfullerene OSCs is not fully understood yet. In this work, we report our effort to understand the stability of nonfullerene OSCs, made with the binary blend poly[(2,6-(4, 8-bis(5-(2-ethylhexyl) thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′] dithiophene-4,8-dione)] (PBDB-T):3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2b:5,6-b′] dithiophene (ITIC) system. It shows that a continuous vertical phase separation process occurs, forming a PBDB-T-rich top surface and an ITIC-rich bottom surface in PBDB-T:ITIC BHJ during the aging period. A gradual decrease in the built-in potential (V 0 ) in the regular configuration PBDB-T:ITIC OSCs, due to the interfacial reaction between the poly(3,4ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) hole transporting layer and ITIC acceptor, is one of the reasons responsible for the performance deterioration. The reduction in V 0 , caused by an inevitable reaction at the ITIC/PEDOT:PSS interface in the OSCs, can be suppressed by introducing a MoO 3 interfacial passivation layer. Retaining a stable and high V 0 across the BHJ through interfacial modification and device engineering, e.g., as seen in the inverted PBDB-T:ITIC OSCs, is a prerequisite for efficient and stable operation of nonfullerene OSCs.

The present band‐selective photodetection is realized by incorporating different optical filters with broadband photodetectors (PDs). However, the use of the optical filters reduces the overall PD sensitivity. This work reports on the effort to develop high‐performance filter‐free band‐selective organic photodetectors (OPDs) having a heterostructure photoactive layer architecture, comprising a semiconducting shorter‐wavelength light depletion layer and a bulk heterojunction (BHJ) layer with an extended absorption to longer wavelengths. The filter‐free band‐selective photodetection is realized by adjusting the difference in wavelengths between the transmission cut‐off wavelength of the semiconducting light depletion layer and the absorption edge of the BHJ layer. For example, a filter‐free visible‐blind near‐infrared OPD, with a spectral rejection ratio of 100, a high responsivity of 0.39 A W−1, a high −3 dB cutoff frequency of 80 kHz, and a fast response time of ≈7 µs, is demonstrated, offering an exciting option for a plethora of applications in imaging and light communications.

We report our effort to unravel the origin of efficient operation of nonfullerene organic solar cells (OSCs), based on a poly[4,8-bis(5-(2-ethylhexyl) thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)](PTB7-Th):3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno [1,2-b:5,6-b']dithiophene (ITIC) blend system. The effects of buildup of space charges, charge extraction, and bimolecular recombination processes on the performance and the stability of PTB7-Th:ITIC-based regular and reverse configuration OSCs are analyzed. It is found that the high-performing inverted PTB7-Th:ITIC OSCs benefit from the combined effects of (1) suppression of bimolecular recombination enabled by an augmented effective internal electric field and (2) improvement of charge extraction by avoiding the holes passing through ITIC-rich region, which would otherwise occur in a regular configuration cell. The inverted PTB7-Th:ITIC OSCs possess a significant improvement in the cell stability and a high power conversion efficiency of ∼8.0%, which is >29% higher than that of an optimized regular configuration control cell (6.1%).

The development of solution-processed photovoltaic (PV) devices for indoor applications has recently attracted widespread attention owing to their outstanding potential in harvesting energy efficiently for low-power-consumption electronic devices, such as...

The effect of 2-D photonic-structures on omnidirectional and broadband light absorption enhancement in organic solar cells (OSCs) is analysed using a combination of theoretical simulation and experimental optimization. The photonic structures in the active layer, with a blend system of poly[4,8-bis[(2-ethylhexyl)oxy] benzo[1,2-b:4,5-bA] dithiophene-2, 6-diyl][3-fluoro-2-[(2-ethylhexyl) carbonyl]thieno[3,4-b]-thiophenediyl] :[6,6]-phenyl-C70butyric-acid-methyl-ester (PTB7:PC70BM), were prepared by the nanoimprint method. It shows that the 2-D photonic structures enable not only broadband but also omnidirectional absorption enhancements in the PTB7:PC70BM-based OSCs over a broader angle range of the incident light, leading to >11 % increase in the power conversion efficiency, as compared to an optimal planar control cell. A weak angular dependency on light absorption is a unique feature of the photonic-structured OSCs, which is useful for different applications.

Modification of the HTL helps to attain a high built-in potential (V0) across the BHJ by suppressing the interfacial reaction at the HTL/BHJ interface. It is critical to retain a high and steady V0 to obtain efficient and stable nonfullerene OSCs.

We report our efforts to develop high performing all-solution-processable transparent inverted QD-LEDs by interposing an interface dipole between the ZnO ETL and the quantum dot light-emitting layer.