LiJiong

A series of wide bandgap donor polymers are designed and synthesized by incorporating a monothiophene functionalized with both a fluorine atom and an ester group. Fabricated from nonhalogenated solvent, power conversion efficiencies of 11.39% and 12.11% are achieved for binary and ternary nonfullerene solar cells, respectively.

Abstract

Significant progress has been made in nonfullerene small molecule acceptors (NF‐SMAs) that leads to a consistent increase of power conversion efficiency (PCE) of nonfullerene organic solar cells (NF‐OSCs). To achieve better compatibility with high‐performance NF‐SMAs, the direction of molecular design for donor polymers is toward wide bandgap (WBG), tailored properties, and preferentially ecofriendly processability for device fabrication. Here, a weak acceptor unit, methyl 2,5‐dibromo‐4‐fluorothiophene‐3‐carboxylate (FE‐T), is synthesized and copolymerized with benzo[1,2‐b:4,5‐b′]dithiophene (BDT) to afford a series of nonhalogenated solvent processable WBG polymers P1‐P3 with a distinct side chain on FE‐T. The incorporation of FE‐T leads to polymers with a deep highest occupied molecular orbital (HOMO) level of −5.60−5.70 eV, a complementary absorption to NF‐SMAs, and a planar molecular conformation. When combined with the narrow bandgap acceptor ITIC‐Th, the solar cell based on P1 with the shortest methyl chain on FE‐T achieves a PCE of 11.39% with a large V _oc of 1.01 V and a J _sc of 17.89 mA cm⁻². Moreover, a PCE of 12.11% is attained for ternary cells based on WBG P1, narrow bandgap PTB7‐Th, and acceptor IEICO‐4F. These results demonstrate that the new FE‐T is a highly promising acceptor unit to construct WBG polymers for efficient NF‐OSCs.

A low bandgap nonfullerene acceptor (NFA) is incorporated into fullerene electron‐transporting layer (ETL) of an inverted perovskite solar cell aiming to intercept the NIR light passing through the device. However, it cannot enhance the device's NIR photoresponse. Further adding a p‐type polymer effectively enhances the device's NIR photoresponse due to better cascade energy‐level alignment and increased hole mobility.

Abstract

How to extend the photoresponse of perovskite solar cells (PVSCs) to the region of near‐infrared (NIR)/infrared light has become an appealing research subject in this field since it can better harness the solar irradiation. Herein, the typical fullerene electron‐transporting layer (ETL) of an inverted PVSC is systematically engineered to enhance device's NIR photoresponse. A low bandgap nonfullerene acceptor (NFA) is incorporated into the fullerene ETL aiming to intercept the NIR light passing through the device. However, despite forming type II charge transfer with fullerene, the blended NFA cannot enhance the device's NIR photoresponse, as limited by the poor dissociation of photoexciton induced by NIR light. Fortunately, it can be addressed by adding a p‐type polymer. The ternary bulk‐heterojunction (BHJ) ETL is demonstrated to effectively enhance the device's NIR photoresponse due to the better cascade‐energy‐level alignment and increased hole mobility. By further optimizing the morphology of such a BHJ ETL, the derived PVSC is finally demonstrated to possess a 40% external quantum efficiency at 800 nm with photoresponse extended to the NIR region (to 950 nm), contributing ≈9% of the overall photocurrent. This study unveils an effective and simple approach for enhancing the NIR photoresponse of inverted PVSCs.

An FTO/TiO 2 /MoO 3 based UV detector has been fabricated through the synthesis of TiO 2 nanowires (NWs) on FTO using the hydrothermal method, the preparation of MoO 3 on TiO 2 NWs by the spin-coating method, after the hydrothermal synthesis, and the preparation of Ag electrodes on the FTO and MoO 3 . The detector exhibits an excellent performance of photo-to-dark current ratio of more than two orders of magnitude. This performance is produced because the dark current under 2.2 V bias has been significantly inhibited due to the electronic potential well formed by the energy band distribution while the photocurrent has increased in comparison with FTO/TiO 2 based detectors under the same conditions which also have a higher photo-to-dark current ratio without the MoO 3 content. Not only does this study take advantage of 1D NWs and 2D nanostructures, but it also provides a new way to inhibit the dark curr...

Perovskite white light-emitting devices (WLEDs) without intercalation layers have not been achieved due to the ion exchange. Although the intercalation layers prevent ion exchange between perovskite nanocrystals (NCs), it also creates a new problem of charge imbalance and the structure becomes more complex. In this study, blue emitting ZnCdS/ZnS NCs with high quantum yield and stability are introduced to work with the yellow emission from CsPb(Br/I) 3 perovskite NCs for WLEDs. The WLEDs are constituted of ITO/ZnO/PEI/ZnCdS/ZnS NCs/CsPb(Br/I) 3 NCs/TCTA/MoO 3 /Au. This design avoids ion exchange between different perovskites NCs, and realizes white light emission by simple fabrication. As a result, we achieved the white light coordinates of (0.34, 0.34) and a correlated color temperature of 5153 K.

InAs nanowires (NWs) have been considered to be highly suitable for future nanoscale photonic applications in mid-wave infrared region. However, progress in this area has been seriously hampered because of the poor radiative efficiency of InAs NWs attributed to their non-radiative (NR) surface. Herein, we demonstrated that a significant improvement of optical performances of InAs NWs grown by chemical vapor deposition could be achieved via sulfur passivation process. Luminescence properties of InAs NWs via organic sulfide (ODT) and inorganic sulfide ((NH 4 ) 2 S) passivation were investigated by detailed photoluminescence (PL) measurement, which exhibited ∼17-fold enhancement in the intensity of optical emission compared to unpassivated InAs NWs. Moreover, the results of this investigation revealed that compared to ODT passivation, (NH 4 ) 2 S passivation provided a more effective method to enhance the luminescence intensity even up to room te...

Influence of barrier material and structure on carrier quantum confinement in GaAsBi quantum wells (QWs) is studied comprehensively. Single- and multi-QW structures were grown using solid-state molecular beam epitaxy with conventional rectangular, step-like and parabolically graded AlGaAs barrier designs. It was discovered that room temperature photoluminescence is increased by more than 50 times in the GaAsBi QWs with parabolically graded barriers (PGBs) if compared to standard rectangular and step-like structures. The enhancement of photoluminescence was reproducible within the range of growth parameters. The carrier localization and increase of trapping efficiency in GaAsBi QWs is responsible for observed enhancement in radiative properties of PGB structures. The random potential field fluctuations for carriers were increased up to 44 meV due to the blurred well-barrier interface causing the conditions for Bi content and/or well width variations. Due to the impact of self-org...