From Transistors to Phototransistors by Tailoring the Polymer Stacking

It is universally acknowledged that highly photosensitive transistors are strongly dependent on the high carrier mobility of polymer-based semiconductors. However, the polymer π–π stacking and aggregation, required to increase the charge mobility, conversely inhibit the dissociation of photogenerated charge carriers, in turn accelerating the geminate recombination of electron-hole pairs. To explore the effects of charge mobility and polymer stacking on the photoresponsivity of the phototransistors, here, two alternating copolymers are synthesized, namely P-PPAB-IDT and P-PPAB-BDT, by palladium-catalyzed Stille coupling of PPAB with indaceodithiophene (IDT) or benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl) (BDT) monomers. The polymer P-PPAB-IDT demonstrates a nearly 20 times enhancement in the hole mobility compared to P-PPAB-BDT. Yet, P-PPAB-IDT surprisingly shows no response to white light illumination, whereas P-PPAB-BDT exhibits a significant photoresponse to the same light source with a high light-current/dark-current (Ilight/Idark) ratio of 21.6 in the p-type area and a low current ratio of just 5.2 in the n-type area. It is believed that this work will provide an effective strategy to develop highly photosensitive polymer semiconductors by reducing polymer stacking and aggregation rather than improving the charge carrier mobility.acceptedVersionPeer reviewe

Sulfonated Dopant-Free Hole-Transport Material Promotes Interfacial Charge Transfer Dynamics for Highly Stable Perovskite Solar Cells

The integration of a functional group into dopant-free hole-transport materials (HTMs) to modify the perovskite|HTM interface has become a promising strategy for high-performance and stable perovskite solar cells (PSCs). In this work, a sulfonated phenothiazine-based HTM is reported, namely TAS, which consists of a butterfly structure with a readily synthesized N,​N-​bis[4-​(methylthio)​phenyl]​aniline side functional group. The interaction between TAS and perovskite via Pb–S bond induces a dipole moment that deepens the valence band of perovskite and thereby leads to enhanced open-circuit voltage in corresponding n-i-p PSCs. More importantly, the functionalization of perovskite surface via Pb–S bond promotes the hole extraction reaction while suppressing the interfacial non-radiative recombination, contributing to a 20–50% performance improvement compared to less- (4-​(methylthio)​-​N-​[4-​(methylthio)​phenyl]​aniline, DAS) or non-interacting (N,N-bis(4-methoxyphenyl)aniline, TAO) counterparts. Consequently, TAS-based PSCs exhibit superior device stability with a high PCE retention (>90% of the initial value) after 125 days of storage in the air.acceptedVersionPeer reviewe

Enhancing the Microstructure of Perovskite-Inspired Cu-Ag-Bi-I Absorber for Efficient Indoor Photovoltaics

Lead-free perovskite-inspired materials (PIMs) are gaining attention in optoelectronics due to their low toxicity and inherent air stability. Their wide bandgaps (≈2 eV) make them ideal for indoor light harvesting. However, the investigation of PIMs for indoor photovoltaics (IPVs) is still in its infancy. Herein, the IPV potential of a quaternary PIM, Cu2AgBiI6 (CABI), is demonstrated upon controlling the film crystallization dynamics via additive engineering. The addition of 1.5 vol% hydroiodic acid (HI) leads to films with improved surface coverage and large crystalline domains. The morphologically-enhanced CABI+HI absorber leads to photovoltaic cells with a power conversion efficiency of 1.3% under 1 sun illumination-the highest efficiency ever reported for CABI cells and of 4.7% under indoor white light-emitting diode lighting-that is, within the same range of commercial IPVs. This work highlights the great potential of CABI for IPVs and paves the way for future performance improvements through effective passivation strategies.</p

Flexible organic photovoltaics with star‐shaped non‐fullerene acceptors end‐capped with indene malononitrile and barbiturate derivatives

We report the design and synthesis of three star-shaped non-fullerene (NFA) acceptors, TPA-2T-INCN, TPA-2T-BAB, and TPA-T-INCN, based on triphenylamine (TPA) core and linked through π-conjugated thiophene (T) spacers to different terminal units (3-oxo-2,3-dihydro-1H-inden-1-ylidene) malononitrile, INCN, and 1,3-dimethylbarbituric acid, BAB). These materials were blended with the widely used poly(3-hexylthiophene-2,5-diyl) (P3HT) donor polymer and tested in flexible organic photovoltaics (OPVs). The NFAs capped with the strong electron withdrawing INCN unit performed best in OPVs. Both P3HT:TPA-T-INCN, and P3HT:TPA-2T-INCN blends also showed the highest photoluminescence quenching efficiency (95.8% and 92.6%, respectively). Surprisingly, when reducing the number of T spacers from 2 to 1, the solubility of the NFAs in o-dichlorobenzene increased, leading to easier processing during the OPV fabrication and better surface morphology. This explains the best performance of TPA-T-INCN-based blends in OPVs, with a champion power conversion efficiency of 1.13%.publishedVersionPeer reviewe

Triple A-Site Cation Mixing in 2D Perovskite-Inspired Antimony Halide Absorbers for Efficient Indoor Photovoltaics

publishedVersionPeer reviewe

Halogen Bonded Hole Transport Material Suppresses Charge Recombination and Enhances Stability of Perovskite Solar Cells

Interfaces play a crucial role in determining perovskite solar cells, PSCs performance and stability. It is therefore of great importance to constantly work toward improving their design. This study shows the advantages of using a hole transport material HTM that can anchor to the perovskite surface through halogen bonding XB . A halo functional HTM PFI is compared to a reference HTM PF , identical in optoelectronic properties and chemical structure but lacking the ability to form XB. The interaction between PFI and perovskite is supported by simulations and experiments. XB allows the HTM to create an ordered and homogenous layer on the perovskite surface, thus improving the perovskite HTM interface and its energy level alignment. Thanks to the compact and ordered interface, PFI displays increased resistance to solvent exposure compared to its not interacting counterpart. Moreover, PFI devices show suppressed nonradiative recombination and reduced hysteresis, with a Voc enhancement of bigger equal as 20 mV and a remarkable stability, retaining more than 90 efficiency after 550 h of continuous maximum power point tracking. This work highlights the potential that XB can bring to the context of PSCs, paving the way for a new halo functional design strategy for charge transport layers, which tackles the challenges of charge transport and interface improvement simultaneousl

Antimony-Bismuth Alloying : The Key to a Major Boost in the Efficiency of Lead-Free Perovskite-Inspired Photovoltaics

The perovskite-inspired Cu2AgBiI6 (CABI) material has been gaining increasing momentum as photovoltaic (PV) absorber due to its low toxicity, intrinsic air stability, direct bandgap, and a high absorption coefficient in the range of 105 cm−1. However, the power conversion efficiency (PCE) of existing CABI-based PVs is still seriously constrained by the presence of both intrinsic and surface defects. Herein, antimony (III) (Sb3+) is introduced into the octahedral lattice sites of the CABI structure, leading to CABI-Sb with larger crystalline domains than CABI. The alloying of Sb3+ with bismuth (III) (Bi3+) induces changes in the local structural symmetry that dramatically increase the formation energy of intrinsic defects. Light-intensity dependence and electron impedance spectroscopic studies show reduced trap-assisted recombination in the CABI-Sb PV devices. CABI-Sb solar cells feature a nearly 40% PCE enhancement (from 1.31% to 1.82%) with respect to the CABI devices mainly due to improvement in short-circuit current density. This work will promote future compositional design studies to enhance the intrinsic defect tolerance of next-generation wide-bandgap absorbers for high-performance and stable PVs.Peer reviewe

Two-Dimensional Antimony-Based Perovskite-Inspired Materials for High-Performance Self-Powered Photodetectors

The ongoing Internet of Things revolution has led to strong demand for low-cost, ubiquitous light sensing based on easy-to-fabricate, self-powered photodetectors. While solution-processable lead-halide perovskites have raised significant hopes in this regard, toxicity concerns have prompted the search for safer, lead-free perovskite-inspired materials (PIMs) with similar optoelectronic potential. Antimony- and bismuth-based PIMs are found particularly promising; however, their self-powered photodetector performance to date has lagged behind the lead-based counterparts. Aiming to realize the full potential of antimony-based PIMs, this study examines, for the first time, the impact of their structural dimensionality on their self-powered photodetection capabilities, with a focus on 2D Cs3Sb2I9−xClx and Rb3Sb2I9 and 0D Cs3Sb2I9. The 2D absorbers deliver cutting-edge self-powered photodetector performance, with a more-than-tenfold increase in external quantum efficiency (up to 55%), speed of response (>5 kHz), and linear dynamic range (>four orders of magnitude) compared to prior self-powered A3M2X9 implementations (A+: monovalent cation; M3+: Sb3+/Bi3+; X−: halide anion). Detailed characterization reveals that such a performance boost originates from the superior carrier lifetimes and reduced exciton self-trapping enabled by the 2D structure. By delivering cutting-edge performance and mechanistic insight, this study represents an important step in lead-free perovskite-inspired optoelectronics toward self-powered, ubiquitous light sensing.publishedVersionPeer reviewe

Advances in the Stability of Halide Perovskite Nanocrystals

Colloidal halide perovskite nanocrystals are promising candidates for next-generation optoelectronics because of their facile synthesis and their outstanding and size-tunable properties. However, these materials suffer from rapid degradation, similarly to their bulk perovskite counterparts. Here, we survey the most recent strategies to boost perovskite nanocrystals stability, with a special focus on the intrinsic chemical- and compositional-factors at synthetic and post-synthetic stage. Finally, we review the most promising approaches to address the environmental extrinsic stability of perovskite nanocrystals (PNCs). Our final goal is to outline the most promising research directions to enhance PNCs&rsquo; lifetime, bringing them a step closer to their commercialization