Search

The performance of organic photovoltaics (OPVs) has rapidly increased. Yet, achieving long-term stability in the nano-morphology and thereby sustaining device performance remains challenging. Herein, we show that incorporating in-situ-forming cross-linked thermoset (CLT) matrices into the bulk heterojunction blends is a simple, general, and efficient strategy for high-performing and resilient OPVs. Our simulations and experimental data prove that these high-modulus CLT matrices featuring hydrogen-bonding interactions can freeze the nano-morphology, resulting in long-term thermal and photostable OPV devices. We demonstrate that this approach works efficiently with eight different blends and show that OPV devices can withstand 85°C for 1,000 h without losing performance. Blends with CLT matrices double the energy generated from OPV devices, showing an energy density output of 4,054 mW⋅h cm−2over an 11-week operating period under outdoor conditions. This methodology opens avenues for both developing new thermoset networks for OPV and their use in other optoelectronic applications.

This work discusses the need to enhance charge carrier collection to minimize halide segregation in wide band-gap (WBG) perovskites. Here, we systematically elucidate the impact of valence band maximum (VBM) offsets and energetic barriers formed at the hole transport layer (HTL)/perovskite interface on charge accumulation, its influence on halide segregation, and ultimately on perovskite solar cell (PSC) long-term photostability. To this end, we precisely tune the VBM-HTL energetic levels by employing blends of self-assembled monolayers (SAMs; MeO-2PACz and Br-2PACz) to fabricate customized HTLs for PSCs with three different WBG perovskite photoabsorbers (1.69, 1.81, and 2.00 eV), commonly used in various tandem configurations. We find that optimized energetic alignment at the SAM HTL/perovskite interface significantly enhances the long-term photostability of the WBG PSCs. Our results show that photostability of devices can be predicted when comparing HTL/perovskite interfaces using photoluminescence’s evolution and transient surface photovoltage spectroscopies of half-stacks (glass/metal oxide/HTL/perovskite) in correlation with halide segregation.

Molecular doping is the key to enabling organic electronic devices, however, the design strategies to maximize doping efficiency demands further clarity and comprehension. Previous reports focus on the effect of the side chains, but the role of the backbone is still not well understood. In this study, we synthesize a series of NDI-based copolymers with bithiophene, vinylene, and acetylenic moieties (P1G, P2G, and P3G, respectively), all containing branched triethylene glycol side chains. Using computational and experimental methods, we explore the impact of the conjugated backbone using three key parameters for doping in organic semiconductors: energy levels, microstructure, and miscibility. Our experimental results show that P1G undergoes the most efficient n-type doping owed primarily to its higher dipole moment, and better host–dopant miscibility with N-DMBI. In contrast, P2G and P3G possess more planar backbones than P1G, but the lack of long-range order, and poor host–dopant miscibility limit their doping efficiency. Our data suggest that backbone planarity alone is not enough to maximize the electrical conductivity (σ) of n-type doped organic semiconductors, and that backbone polarity also plays an important role in enhancing σ viahost–dopant miscibility. Finally, the thermoelectric properties of doped P1G exhibit a power factor of 0.077 μW m−1K−2, and ultra-low in-plane thermal conductivity of 0.13 W m−1K−1at 5 mol% of N-DMBI, which is among the lowest thermal conductivity values reported for n-type doped conjugated polymers.

Mixed tin–lead (Sn–Pb) halide perovskites stand out as promising materials for next-generation photovoltaics and near-infrared optoelectronics. However, their sensitivity to oxidative degradation remains a major hurdle toward their widespread deployment. A holistic understanding of their oxidation processes considering all their constituent ions is therefore essential to stabilize these materials. Herein, we reveal that A-site cation choice plays an inconspicuous yet crucial role in determining Sn–Pb perovskite stability toward oxidation. Comparing typical A-site compositions, we show that thin films and solar cells containing cesium are more resistant to oxidative stress relative to their methylammonium analogs. We identify degradation in these compositions to be closely linked to the presence of triiodide, a harmful species evolving from native I2oxidants. We find that hydrogen bonding between methylammonium and I2promotes triiodide formation, while the strong polarizing character of cesium limits this process by capturing I2. Inspired from these findings, we design two strategies to boost stability of sensitive methylammonium-based Sn–Pb perovskite films and devices against oxidation. Specifically, we modulate the polarizing character of surface A-sites in perovskite via CsI and RbI coatings, and we incorporate Na2S2O3as an I2scavenging additive. These crucial mechanistic insights will pave the way for the design of highly efficient and stable Sn–Pb perovskite optoelectronics.

The choice of interfacial materials and their properties play a critical role in determining solar cell performance and stability. For compatibility with roll-to-roll printing, it is desirable to develop stable cathode interface layers (CILs) that can be processed over the photoactive layer using orthogonal solvents. In this study, an n-type naphthalene diimide core and oligo (ethylene glycol) side-chain-based conjugated polymer is reported as a universal, efficient CIL for organic and perovskite photovoltaics. Besides good thermal stability and easy processing in alcohol/water, the new CIL is found to possess electron transport properties with an electrical conductivity of 2.3 × 10–6S cm–1, enabling its use as a CIL with a film thickness of up to ∼35(±2) nm. Utilizing the new CIL, 16% power conversion efficiency (PCE) is achieved for organic solar cells (OSCs) based on the PM6-Y6 photoactive layer (8.9% PCE for no CIL and 15.1% with state-of-the-art CIL, PDINO), and perovskite solar cells from methylammonium lead iodide yielded a PCE of 17.6%. Compared to the reference devices, the new CIL reduced trap-assisted carrier recombination and increased the built-in potential by 80 mV, simultaneously enhancing all photovoltaic parameters. Moreover, new CIL based devices had better photostability with no burn-in losses.

Doping serves as a vital strategy for tuning electronic and optoelectronic properties of semiconductors. Compared to organic semiconductors, the understanding and optimization of the doping process in halide perovskite semiconductors is still in its infancy. Nonetheless, there is a continuous surge in doping these semiconductors for performance enhancement. This perspective discusses the central role of dopants in organic and halide perovskite-based semiconductors used for energy conversion devices, particularly solar cells and thermoelectrics. We summarize various p- and n-type dopants explored for modifying the active layer in organic and perovskite devices, highlighting their challenges and limitations. Understanding doping-induced changes in electronic properties and their ramifications on device performance is essential for improving the device performance.