Carrier Extraction Research Articles

Reinforcing built-in electric field to enable efficient carrier extraction for high-performance perovskite solar cells

This review presents an overview of the carrier separation and extraction mechanism influenced by the built-in electric field (BEF) in PSCs and various strategies used to enhance the BEF.

Gamma-ray dose threshold for MAPbI3 solar cells.

In this work, we report on the effects observed in MAPbI3 polycrystalline films and solar cells under moderate gamma-ray doses of 3-21 kGy. We applied several instrumental techniques such as photoluminescence spectroscopy, time-resolved photoluminescence, Suns-VOC measurement, and impedance spectroscopy to characterize exposed samples. We observed a nonlinear dependency of such characteristics as PL intensity, career lifetime, ideality factor, and recombination resistance on the exposure dose. Small doses of 3-5 kGy annihilate some of the defect centers in the material, which results in improved carrier extraction and prolonged carrier lifetime, while with larger doses of 10 kGy and above, nonradiative recombination becomes predominant. In this way, we revealed a gamma-ray threshold for MAPbI3 films of around 10 kGy, above which it is not recommended to exploit this material. In space environment, yearly doses rarely exhibit 0.1 kGy (10 krad), and the MAPbI3 material has a sufficient margin of safety for space applications. Moreover, this unusual behaviour opens up the opportunity to use gamma-ray sources as an effective method to improve the quality of defective polycrystalline perovskite films before actual exploitation in an ionizing radiation-free environment.

Synergistic dual-layer passivation boosts efficiency and stability in perovskite solar cells using naphthol sulfonate.

The performance and stability of perovskite solar cells (PSCs) are critically influenced by the interfacial properties between the perovskite absorption layer and the electron transport layer (ETL). This study introduces a novel interfacial engineering approach using dipotassium 7-hydroxynaphthalene-1,3-disulfonate (K-NDS) as a multifunctional passivator to enhance both the SnO2 ETL and the perovskite absorber layer. The sulfonic acid groups (-SO3-) in K-NDS effectively fill oxygen vacancies on the SnO2 surface, while the hydroxyl groups (-OH) passivate dangling bonds, improving the crystallinity of the perovskite film. Additionally, the diffusion of K+ from the SnO2 ETL into the perovskite layer optimizes energy level alignment, thereby enhancing charge carrier extraction and transport. This bifacial passivation strategy has significantly improved both the power conversion efficiency (PCE) and long-term stability of PSCs. The modified devices achieved a champion PCE of 23.00% and an open-circuit voltage (VOC) of 1.172 V. Furthermore, these devices maintained 75% of their initial PCE even after 1000 hours of storage under indoor environmental conditions. This work demonstrates the effectiveness of synergistic interfacial passivation in advancing the performance and durability of PSCs.

Dual-Use Self-Assembled Monolayer Controlling Charge Carrier Extraction in Organic Solar Cells.

The development and use of interface materials are essential to the continued advancement of organic solar cells (OSCs) performance. Self-assembled monolayer (SAM) materials have drawn attention because of their simple structure and affordable price. Due to their unique properties, they may be used in inverted devices as a modification layer for modifying ZnO or as a hole transport layer (HTL) in place of typical poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) in conventional devices. In this work, zinc oxide (ZnO) is modified using five structurally similar SAM materials. This resulted in a smoother surface, a decrease in work function, a suppression of charge recombination, and an increase in device efficiency and photostability. In addition, they can introduced asfor hole extraction layer between the active layer and MoO3 , enabling the use of the same material at several functional layers in the same device. Through systematic orthogonal evaluation, it is shown that some SAM/active layer/SAM combinations still offered device efficiencies comparable to ZnO/SAM, but with improved device' photostability. This study may provide recommendations for future SAM material's design and development as well as a strategy for boosting device performance by using the same material across both sides of the photoactive layer in OSCs.

Making and Breaking of Exciton Cooling Bottlenecks in Halide Perovskite Nanocrystals.

Harnessing quantum confinement (QC) effects in semiconductors to retard hot carrier cooling (HCC) is an attractive approach for enabling efficient hot carrier extraction to overcome the Shockley-Queisser limit. However, there is a debate about whether halide perovskite nanocrystals (PNCs) can effectively exploit these effects. To address this, we utilized pump-probe and multipulse pump-push-probe spectroscopy to investigate HCC behavior in PNCs of varying sizes and cation compositions. Our results validate the presence of an intrinsic phonon bottleneck with clear manifestations of QC effects in small CsPbBr3 PNCs exhibiting slower HCC rates compared to those of larger PNCs. However, the replacement of inorganic Cs+ with organic cations suppresses this intrinsic bottleneck. Furthermore, PNCs exhibit distinct size-dependent HCC behavior in response to changes in the cold carrier densities. We attribute this to the enhanced exciton-exciton interactions in strongly confined PNCs that facilitate Auger heating. Importantly, our findings dispel the existing controversy and provide valuable insights into design principles for engineering QC effects in PNC hot carrier applications.

B-Site Co-Doping Coupled with Additive Passivation Pushes the Efficiency of Pb-Sn Mixed Inorganic Perovskite Solar Cells to Over 17.

Pb-Sn mixed inorganic perovskite solar cells (PSCs) have garnered increasing interest as a viable solution to mitigate the thermal instability and lead toxicity of hybrid lead-based PSCs. However, the relatively poor structural stability and low device efficiency hinder its further development. Herein, high-performance manganese (Mn)-doped Pb-Sn-Mn-based inorganic perovskite solar cells (PSCs) are successfully developed by introducing Benzhydroxamic Acid (BHA) as multifunctional additive. The incorporation of smaller divalent Mn cations contributes to a contraction of the perovskite crystal, leading to an improvement in structural stability. The BHA additive containing a reductive hydroxamic acid group (O═C-NHOH) not only mitigates the notorious oxidation of Sn2+ but also interacts with metal ions at the B-site and passivates related defects. This results in films with high crystallinity and low defect density. Moreover, the BHA molecules tend to introduce a near-vertical dipole moment that parallels the built-in electric field, thus facilitating charge carrier extraction. Consequently, the resulting device delivers a champion PCE as high as 17.12%, which represents the highest reported efficiency for Pb-Sn-based inorganic PSCs thus far. Furthermore, the BHA molecule provides an in situ encapsulation of the perovskite grain boundary, resulting in significant enhancement of device air stability.

Enhancing charge carrier extraction and energy band alignment in perovskite solar cells using interfacial passivation with polar organic molecules

The wide utilization of perovskite material as an absorber layer in solar cells necessitates favorable alignment with the perovskite's conduction band, governed by FTO/TiO2 (SnO2). Instead of an ideal electric-selective contact, further improvement of the hole-selective contact is crucial to enhance hole extraction and minimize carrier recombination at the interface between perovskite and spiro-OMeTAD. In this study, we employed series of polar organic molecules [2,4-dimethyl-6,8-bis(4-(methylthio)phenyl)pyrrolo [1,2-a]pyrimidine-7-carbonitrile (PCNS), 2,4-dimethyl-6,8-diphenylpyrrolo [1,2-a]pyrimidine-7-carbonitrile (PCN), and 2,4-dimethyl-6-8-(pyren-1-yl)pyrrolo [1,2-a]pyrimidine-7-carbonitrole (PCNP)] with cyano groups as the interfacial passivate layer to facilitate energy band matching between the perovskite and the hole transport layer as confirmed by the energy band bending at the perovskite surface. Consequently, we achieved effective charge carrier extraction and suitable bandgap alignment. A detailed comparative analysis of the photophysical and electrical properties among the three molecules elucidated the origin of higher open circuit voltage (1.18 ​V) and improved fill factor (83.15 %) in the solar cell device based on PCN molecule (24.22 %).

Insight into Air Degradation of Inverted Perovskite Solar Cells with Different Cathode Interlayers.

Air stability is a big challenge for inverted perovskite solar cells (IPVSCs). We focus on effect of a cathode interlayer (BCP or TOASiW12) on air degradation of IPVSCs with an Al or Ag cathode. Combined measurements have been carried out to check the changes of the device electrical performance with exposure to air. Our results demonstrated that the IPVSCs with BCP/Al suffered an overall deterioration in terms of dissociation of excitons, transport, and extraction of charge carriers, which was accompanied by improved trap density and serious trap-induced recombination when exposed to air. Instead, all the electrical characteristics of the IPVSCs with TOASiW12/Al, BCP/Ag and TOASiW12/Ag remained stable or slightly reduced after exposed to air over 2 days. This work provides new insight into the air aging of IPVSCs and facilitates the development of CIL materials for cost-effective IPVSCs.

(Invited) In Situ Photoelectron Spectroscopy Reveals the Chemical Nature of Semiconductor Surface States

The accessible photovoltage of semiconducting photoabsorbers is typically 0.5-1 V below the theoretically achievable values predicted by the Shockley-Queisser limit [1]. Although the reason for this is still not well understood, surface and interface states within the photoabsorbers energy band gap may play a crucial role as they generally induce Fermi level pinning [2]. Within the PEC community, two key elements have been identified for the maximization of the photovoltage in photoelectrodes for water splitting: (i) the passivation of surface defects which is needed to avoid Fermi level pinning, and (ii) the increase of the minority carrier concentration at the interface to improve contact selectivity and optimize carrier extraction [3,4].To understand the role of surface defects on Fermi level pinning, detailed information on the chemical nature and electronic properties of surface states is needed. Such information is usually obtained with UHV surface science techniques such as XPS, but the photoelectrode surface under UHV conditions has little, if any, relevance to the electrified surface when immersed in the electrolyte. Moreover, recent studies have shown that semiconductor surfaces are not static, but undergo extensive structural and chemical transformations during PEC device operation [5,6]. In this talk, we will show our recent development of state-of-the-art techniques to study the structure and dynamics of semiconductor/water interfaces under practically relevant conditions [7]. The chemical nature of the electronic states for selected semiconductors prepared at the Institute for Solar Fuels has been explored using synchrotron-based resonant, ambient pressure soft and hard X-ray photoelectron spectroscopy (AP-XPS and AP-HAXPES) [6,8-11], and with in situ/operando Raman and photoluminescence spectroscopy. In particular, we will show that it is possible to study photon-induced chemical changes at solid/liquid interfaces using AP-XPS and AP-HAXPES [6,8].We will conclude this contribution by discussing about future perspectives and technical implementations for multimodal in situ/operando investigations of photoelectrocatalytic processes.[1] M.T. Mayer. Curr. Opin. Electrochem. 2017, 2, 104.[2] A. J. Bard et al. J. Am. Chem. Soc. 1980, 102, 3671.[3] A.G. Scheuermann et al., Nat. Mater. 2016, 15, 99.[4] M. Schleuning et al., Sustainable Energy Fuels, 2022, 6, 3701.[5] F.M. Toma et al., Nat. Commun. 2016, 7, 12012.[6] M. Favaro et al., J. Phys. Chem. B 2018, 122, 801.[7] M. Favaro et al., Surf. Sci. 2021, 713, 121903.[8] M. Favaro et al., J. Phys. D: Appl. Phys. 2021, 54, 164001.[9] M. Favaro et al., J. Phys. Chem. C 2019, 123, 8347.[10] W. Wang et al., J. Am. Chem. Soc. 2022, 144, 17173.[11] P. Schnell et al., Sol. RRL 2023, 2201104.

Electronic sensitization by Mg doping gradient-induced functional interfaces: Large photocurrent in PbS/Zn1-xMgxO solar cells

We investigated doping gradient-mediated charge separation and carrier extraction in PbS/ZnMgO photovoltaic (PV) devices. We fabricated PbS/Zn(Mg)O/Al solar cells in which the Mg composition was systematically changed to form the PbS/Zn0.85Mg0.15O and PbS/ZnO interfaces where charge separation and extraction occur, respectively, during PV operation. The short-circuit current increased significantly with the Mg-doping gradient electron transport layer (ETL). The increased short-circuit current is attributed to the suppression of carrier recombination at the PbS/ Zn0.85Mg0.15O interface and the enhanced carrier extraction at the ZnO/Al interface resulting from the formation of Mg doping gradient in the ETL. The presented results provide insights into the synergistic effect of the doping gradient ETL and interface modification for the electronic sensitization of PbS colloidal quantum dot PV devices.

Novel cathode buffer layer enabling over 21.6%/20.9% efficiency in wide bandgap/inorganic perovskite solar cells

Different types of hybrid organic/inorganic halide perovskite solar cells (PSCs) have attracted extensive research attention and showed extremely considerable practical application potential in current energy field, for instance, wide bandgap (WBG) PSCs are widely used in fabricating high-efficiency tandem devices, while inorganic perovskite solar cells (IPSCs) had been sought after by researchers due to its excellent thermal stability. However, either WBG PSCs or IPSCs were severely influenced by the carrier extraction and transport between the electron transfer layer and anode/cathode. On this basis, an in-situ oxygen plasma treated Ti doped ZnO film named TZO (O) was used as cathode buffer layer to regulate the energy-level alignment between the SnO2 layer and ITO electrode, optimize the crystal quality of perovskite and passivate perovskite defects through providing superior SnO2 film. It is found that the more suitable energy levels for the interlamination availably polished up carrier transport effect to a great extent, which could be seen in steady-state and time-resolved photoluminescence spectra, in addition to this, the perovskite film covered on TZO (O)/ SnO2 demonstrated larger perovskite crystals and less surface defects. As a consequence, the power conversion efficiency (PCE) of the optimized device with a bandgap of ≈ 1.66 eV up to 21.62%, and the efficiency of CsPbI2.85Br0.15 IPSCs is enhanced from 19.21% to 20.92%. Moreover, the unencapsulated TZO (O)-treated wide bandgap PSCs shows enhanced stability, retaining 89.47% of its initial efficiency after 1000 h in a N2 filled environment, while the unencapsulated IPSCs-based TZO (O) still remains 83.77% of its initial efficiency under continuous illumination in air for 325 h. This work exhibited that the buffer layer TZO (O) is a promising interfacial modification material for both n-i-p type wide bandgap PSCs and IPSCs.

Au Nanocluster Assisted Microstructural Reconstruction for Buried Interface Healing for Enhanced Perovskite Solar Cell Performance.

The heterogeneity of perovskite film crystallization along the vertical direction leads to voids and traps at the buried interfaces, hampering both efficiency and stability of perovskite solar cells. Here, bovine serum albumin-functionalized Au nanoclusters (ABSA), combined with heavy gravity, high surface charge density, and strong interactions with the electron transport layer, are designed to reconstruct the buried interfaces for not only high-quality crystallization, but also improved carrier transfer. The ABSA macromolecules with amine function groups and larger surface charge density interact with the perovskite to improve the crystallinity, and gradually migrate towards the buried interface, healing the defective voids, hence suppressing surface recombination velocity from 3075 to 452 cm s-1 . The healed buried interface and the higher surface potential of ABSA-modified TiO2 lead to improved carrier extraction at the interface. The resulting solar cell attains a power conversion efficiency of 25.0% with negligible hysteresis and remarkable stability, maintaining 92.9% of their initial efficiency after 3200 h of exposure to the ambient atmosphere, they also exhibit better continuous irradiation stability compared to control devices. These findings provide a new metal-protein complex to eliminate the deleterious voids and defects at the buried interface for improved photovoltaic performance and stability.

Aqueous solution processed electron-transporting layer based on organosilica nanodots for highly efficient and stable inverted organic solar cells

In this work, we synthesis a new electron-transporting layer material for inverted organic solar cells(i-OSCs) based on organosilica nanodots. The material is synthesized by a simple one-step hydrothermal reaction of 3-[2-(2-aminoethylamino)ethylamino] propyl-trimethoxysilane (AEEA) with carminic acid in water solvent (OSi-CA). Compared with ZnO-based devices, OSi-CA based devices show improved carrier extraction, higher PCE, and greatly increased device stability under UV irradiation. With PM6:Y6 as the active layer, OSi-CA based device has a PCE of 16.01 %. In addition, the OSi-CA electron-transporting layer significantly improves the photostability of OSCs. After 600 min of continuous UV lamp (5 mW cm−2) irradiation, the OSi-CA based i-OSC retained 95.5 % of its initial performance, whereas the ZnO-based device had only 71.2 %.

Surface Energy Engineering of Buried Interface for Highly Stable Perovskite Solar Cells with Efficiency Over 25.

The abundant oxygen-related defects (e.g., O vacancies, O-H) in the TiO2 electron transport layer results in high surface energy, which is detrimental to effective carrier extraction and seriously impairs the photovoltaic performance and stability of perovskite solar cells. Here, novel surface energy engineering (SEE) is developed by applying a surfactant of heptadecafluorooctanesulfonate tetraethylammonium (HFSTA) on the surface of the TiO2 . Theoretical calculations show that the HFSTA-TiO2 is less prone to form O vacancies, leading to lower surface energy, thus improving the carrier-extraction efficiency. The experimental results show that superior perovskite film is obtained due to the reduced heterogeneous nucleation sites and improved crystallization process on the modified TiO2 . Furthermore, the flexible long alkyl chains in HFSTA considerably relieve the compressive stresses at the buried interface. By combining the passivation of TiO2 , crystallization process modulation, and stress relief, a champion PCE up to 25.03% is achieved. The device without encapsulation sustains 92.2% of its initial PCE after more than 2500h storage under air ambient with relative humidity of 25-30%. The SEE of a buried interface paves a new way toward high-efficiency, stable perovskite solar cells.

Multifunctional Regulation of SnO2 Nanocrystals by Snail Mucus for Preparation of Rigid or Flexible Perovskite Solar Cells in Air.

Tin oxide (SnO2) is widely used as an inorganic electron transport layer (ETL) for rigid and flexible perovskite solar cells (PSCs). In this work, an extract of snail shell, the sodium salt of polyaspartic acid (S-PASP), a water-soluble polypeptide polymer, has been used to multifunctionally regulate SnO2 nanograins. S-PASP has a strong chelating and dispersing effect; thus, chemically adsorbed SnO2 can inhibit agglomeration. The S-PASP:SnO2 ETL also improved the extraction and transferability of carriers, reducing body defects and interfacial charge. Moreover, the S-PASP:SnO2 ETL promotes the vertical growth of the perovskite crystals due to its bottom-up morphology, wettability, and strain release, which is conducive to improving the photoelectric performance of the device. The optimized rigid device prepared under open-air conditions obtained a PCE of 20.92%. In addition, due to the stress compensation of the S-PASP long chain, which prevented the cracking and displacement of the ETL, the optimal PCE of the flexible device was 17.96%, and the initial efficiency was maintained at 82.8% after 100 bends. This work introduces a molecular doping mechanism for organic-inorganic hybrid electronics.

Auxiliary Buried‐Interface Passivation Toward Stable and Low‐Recombination‐Loss Perovskite Photovoltaics

Defects occur in the bulk perovskite and heterojunction interfaces of perovskite solar cells (PSCs). While additive and interface engineering are commonly used to passivate defects within the perovskite phase and at the interface, the interconnections between these two strategies have not been fully explored. This study introduces an auxiliary passivation approach for enhancing the performance of PSCs by passivating both the perovskite phase and the buried interface using succinimide (SID), referred to as the multilayer passivation (MLP) strategy. By adding SID to a lead iodide precursor solution and depositing it on tin oxide film, the remarkable ability of SID to coordinate with Pb2+ through Lewis‐base coordination and bind the iodide ion with hydrogen bonds is demonstrated, thereby reducing defects within the perovskite and suppressing nonradiative recombination. Additionally, SID could passivate oxygen vacancy and hydroxyl defects on the SnO2 surface, facilitating carrier separation and extraction. This MLP strategy enables us to achieve a power conversion efficiency (PCE) of 24.47% based on a two‐step process. Moreover, the unencapsulated devices maintain a PCE of 82% at 20 °C with 30% relative humidity after 7000 h. Overall, this study highlights the unparalleled potential of MLP strategy for enhancing the performance of PSCs.

Bandgap Engineering of Two‐Step Processed Perovskite Top Cells for Perovskite‐Based Tandem Photovoltaics

AbstractFor high‐performance application of perovskite solar cells (PSCs) in monolithic perovskite/silicon tandem configuration, an optimal bandgap and process method of the perovskite top cell is required. While the two‐step method leads to regular perovskite film crystallization, engineering wider bandgaps (Eg > 1.65 eV) for the solution‐based two‐step method remains a challenge. This work introduces an effective and facile strategy to increase the bandgap of two‐step solution‐processed perovskite films by incorporating bromide in both deposition steps, the inorganic precursor deposition (step 1, PbBr2) and the organic precursor deposition (step 2, FABr). This strategy yields improved charge carrier extraction and quasi‐Fermi level splitting with power conversion efficiencies (PCEs) of up to 15.9%. Further improvements are achieved by introducing CsI in the bulk and utilizing LiF as surface passivation, resulting in a stable power output exceeding 18.5% for Eg = 1.68 eV. This additional performance boost arises from enhanced perovskite film crystallization, leading to improved charge carrier extraction. Laboratory scale monolithic perovskite/silicon solar cells (TSCs) (1 cm2 active area) achieve PCEs up to 23.7%. This work marks a significant advancement for wide bandgap two‐step solution‐processed perovskite films, enabling their effective use in high‐performance and reproducible PSCs and perovskite/silicon TSCs.

Constructing tin oxides Interfacial Layer with Gradient Compositions for Efficient Perovskite/Silicon Tandem Solar Cells with Efficiency Exceeding 28.

Atomic layer deposition (ALD) growth of conformal thin SnOx films on perovskite absorbers offers a promising method to improve carrier-selective contacts, enable sputter processing, and prevent humidity ingress toward high-performance tandem perovskite solar cells. However, the interaction between perovskite materials and reactive ALD precursor limits the process parameters of ALD-SnOx film and requires an additional fullerene layer. Here, it demonstrates that reducing the water dose to deposit SnOx can reduce the degradation effect upon the perovskite underlayer while increasing the water dose to promote the oxidization can improve the electrical properties. Accordingly, a SnOx buffer layer with a gradient composition structure is designed, in which the compositionally varying are achieved by gradually increasing the oxygen source during the vapor deposition from the bottom to the top layer. In addition, the gradient SnOx structure with favorable energy funnels significantly enhances carrier extraction, further minimizing its dependence on the fullerene layer. Its broad applicability for different perovskite compositions and various textured morphology is demonstrated. Notably, the design boosts the efficiencies of perovskite/silicon tandem cells (1.0cm2) on industrially textured Czochralski (CZ) silicon to a certified efficiency of 28.0%.

Fully Printed High‐Performance Quasi‐Two‐Dimensional Perovskite Solar Cells via Multifunctional Interfacial Engineering

AbstractPlanar n–i–p carbon perovskite solar cells (PSCs) with a hole transport layer that can be fabricated at low temperatures at low‐cost exhibit great potential for large‐scale manufacturing. Moreover, 2D perovskites have attracted considerable attention owing to their higher stability. In this work, scalable and highly efficient fully printed large‐area carbon electrode‐based 2D perovskite modules are reported through the insertion of a thin naphthaleneimide derivative (CATNI)‐based interfacial layer between tin (IV) oxide and the perovskite layer. The results show that this facilitates the formation of the interfacial contact, suppresses energy losses, and substantially improves the performance parameters of the PSCs, especially their VOC value. A significantly enhanced VOC of 1.13 V is achieved resulting in the device PCE value reaching over 18%, which is one of the highest reported for fully printed PSCs so far. It is found that with the deployment of this CATNI‐based interfacial layer, a more efficient carrier extraction is achieved. This ultimately contributed to enhanced spectral response as well as improved VOC for these carbon electrodes based on fully printed devices. Finally, the carbon‐perovskite solar modules (carbon‐PSMs) are fabricated on ITO glass substrates with dimensions of 5.0 × 5.0 cm. These prepared modules exhibited outstanding photovoltaic performance with the highest PCE value of over 14.6%.

Thermally Activated Delayed Fluorescence Triplet State Excitons for High‐Performance Organic Photodetectors: A Novel Strategy

AbstractPhotoinduced charge‐trapping is a promising strategy for boosting the photosensitivity of organic photodetectors at the expense of their response time. In addition, they have a low carrier extraction yield due to the formation of low‐energy triplet excitons through the recombination of a photogenerated hole–electron pair. Materials with thermally activated delayed fluorescence (TADF) exhibit a long‐lived (≈µs) excited spin‐triplet nearly iso‐energetically aligned with that of an excited spin‐singlet, which results in suppressed exciton losses and is widely used in organic light‐emitting diodes. The extraction and population of triplet state excitons in TADFs is a sought‐after but underexplored aspect of photoinduced gating in photodetectors. A 1,2,3,5‐tetrakis(carbazol‐9‐yl)4,6‐Dicyanobenzene (4CzIPN) TADF blend with a high‐mobility Poly[2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene] (PBTTT‐C14) polymer via bulk type‐II offset can increase free carrier extraction yield (fast response) and retain trapped electrons in TADF triplet states (high gain). The PBTTT‐C14/4CzIPN ultraviolet photodetector device maintains a trade‐off between high photogain (≈103) and fast response time (79 ms) at 300 nm while operating at a shallow dark current (≈pA). Furthermore, the device shows high external quantum efficiency (≈104 %) and detectivity (≈1011 Jones) for low light power (<pW). The innovative application of TADF material can lead to exciting new developments in organic‐based high‐performance photodetection.