Hole Blocking Effect Research Articles

Performance of perovskite solar cells based on SnO<sub>2</sub>:DPEPO hybrid electron transport layer

The electron transport layer is an important functional layer of perovskite solar cells, and its surface and internal defects are critical parts of limiting the performance improvement of perovskite solar cells. The double electron transport layer (double ETL) strategy can effectively passivate inherent defects in the electron transport layer (such as SnO<sub>2</sub>) and improve electron extraction and transport between the functional layers, providing an effective way for developing efficient and stable PSCs. However, due to the existence of independent interfaces in the dual ETL, the cell mismatch in different ETL materials also leads to additional carrier defects, hindering the continuous advancement of the dual ETL strategy. This work proposes a strategy for introducing di[2-((oxo)diphenylphosphino)phenyl]ether (DPEPO) into SnO<sub>2</sub> ETL to design a hybrid electron transport layer strategy. Using the hole-blocking effect of DPEPO, which has a higher HOMO energy level and good ability to transfer electrons, the intrinsic defects in SnO<sub>2</sub> are successfully passivated, while significantly improving the crystalline quality of the SnO<sub>2</sub> film surface. So, avoiding the direct contact between the perovskite photoactive layer and the conductive substrate can effectively improve the extraction and transport of electrons. Due to the preparation of high-quality electron transport layer, the crystallization regulation of perovskite thin film is further achieved, thereby improving the performance of perovskite solar cells. Finally, 21.53% of the power conversion rate is obtained, the open-circuit voltage (<i>V</i><sub>OC</sub>) reaches 1.220 V, the short-circuit current (<i>J</i><sub>SC</sub>) is 23.19 mA/cm<sup>2</sup>, and the fill factor (FF) is 76.11%. This efficiency is 1.39% higher than that of the control one. It is shown that the hybrid electron transport layer strategy can not only optimize the carrier transport dynamics efficiently and reduce the device performance affected by the defects in the functional layer significantly, but also regulate the perovskite crystallization, which has the prospect for preparing high-performance solar cells.

Bilayer phosphine oxide modification toward efficient and large-area pure-blue perovskite quantum dot light-emitting diodes

Blue emissive halide perovskite light-emitting diodes (LEDs) are gaining increasing attention. Reducing defects in halide perovskites to improve the performance of the resulting LEDs is a main research direction, but there are limited passivation methods for achieving efficient and spectrally-stable pure-blue LEDs based on mixed-halide perovskites. In this work, double modification layers containing phosphine oxides, i.e., diphenyl[4-(triphenylsilyl)phenyl]phosphine oxide (TSPO1) and 2,7-bis(diphenylphosphoryl)-9,9′-spirobifluorene (SPPO13), are developed to passivate mixed-halide perovskite quantum dot (QD) films. The comprehensive spectroscopic and structural characterization results indicate the presence of strong interactions between TSPO1/SPPO13 and the QDs. Besides, the combination of the bilayer exhibits a synergistic hole-blocking effect, improving the charge balance of the LEDs. LEDs based on the QD/TSPO1/SPPO13 films deliver stable electroluminesence at 469 nm and present a maximum external quantum efficiency (EQE) and luminance of 4.87% and 560 cd m−2, respectively. Benefiting from the uniform QD/TSPO1/SPPO13 film over a large area, LEDs with an area of 64 mm2 show a maximum EQE of 3.91%, which represents the first efficient large-area mixed-halide perovskite LED with stable pure-blue emission. This work provides a method to improve the perovskite QDs-based film quality and optoelectronic properties, and is a step toward the fabrication of highly-efficient large-area blue perovskite LEDs.

Back interface passivation for ultrathin Cu(In,Ga)Se2 solar cells with Schottky back contact: A trade-off of electrical effects

Back interface passivation reduces the back recombination of photogenerated electrons, whereas aggravates the blocking of hole transport towards back contact, which complicate the back interface engineering for ultrathin CIGSe solar cells with a Schottky back contact. In this work, theoretical explorations were conducted to study how the two contradictory electrical effects impact cell performance. For ultrathin CIGSe solar cells with a pronounced Schottky potential barrier (E h > 0.2 eV), back interface passivation produces diverse performance evolution trends, which are highly dependent on cell structures and properties. Since a back Ga grading can screen the effect of reduced recombination of photogenerated electrons from back interface passivation, the hole blocking effect predominates and back interface passivation is not desirable. However, when the back Schottky diode merges with the main pn junction due to a reduced absorber thickness, the back potential barrier and the hole blocking effect is much reduced on this occasion. Consequently, cells exhibit the same efficiency evolution trend as ones with an Ohmic contact, where back interface passivation is always advantageous. The discoveries imply the complexity of back interface passivation and provide guidance to manipulate back interface for ultrathin CIGSe solar on TCOs with a pronounced Schottky back contact.

P-AlInN electron blocking layer for AlGaN-based deep-ultraviolet light-emitting diode

Commonly, the Al-rich AlGaN layer acts as electron blocking layer (EBL) to block the overflow of electrons from the active region in conventional AlGaN deep-ultraviolet (DUV) light-emitting diode (LED). However, the Al-rich AlGaN layer leads to the disadvantages of severe electron overflow and hole blocking effect. Herein, we proposed a new AlInN-based EBL to improve the optoelectronic characteristics of AlGaN-based DUV LED. The calculated results show that conventional (fixed Al composition) AlInN EBL has superior hole injection, reduced electron overflow, and lower electric field as compared to conventional AlGaN EBL. By using AlInN EBL, internal quantum efficiency (IQE) drop is reduced by 20%, and light output power improved by 165.30%. It was noticed that conventional AlInN EBL has a 28% IQE drop which can further be minimized by employing AlInN/AlInN superlattice EBL structure. It is found that superlattice EBL improved carrier distribution and reduced electric field resulting in a higher electron-hole wave-function overlap of 55% within multiple quantum wells (MQW) which elevate radiative recombination rate. AlInN superlattice EBL LED has drop-free 93% IQE, twice light output power, and spontaneous emission rate compared to conventional AlInN EBL LED.

Enhancing the Luminous Efficiency of Ultraviolet Light Emitting Diodes By Adjusting the Al Composition of Pre-Well Superlattice

The lower luminous efficiency is a critical issue for ultraviolet light-emitting diodes (UV-LEDs) owing to the poor carrier injection efficiency and high dislocation density. Here, we can improve the luminous efficiency in two avenues by adjusting the Al composition of the InGaN/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> N pre-well superlattice. First, due to the strain-induced piezoelectric and intrinsic spontaneous polarization, a large number of electrons gather at the InGaN/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> N interface, which improves the electron concentration of the pre-well superlattice and lowers the conduction band energy of the first quantum barrier layer (FQB), thus enhancing the electron injection efficiency. Second, the pre-well superlattice can act as a hole blocking layer to prevent holes from leaking into the n-type layer and confine them in the quantum well layer. As the Al composition increases, the hole blocking effect of the pre-well superlattice is strengthened. However, higher Al composition decreases the lattice quality, which makes it possible for carrier loss through defect-related non-radiative recombination. Finally, the output power of the samples with 5% Al composition in the pre-well superlattice is 5.9% and 102.5% higher than that of the samples with 3% and 7% Al composition, respectively.

Simulation Study of Novel Trench Gate U-Shaped Channel SOI Lateral IGBTs With Suppressed Gate Voltage Overshoot and Reduced di/dt

The gate voltage overshoot during the turn-on transient in the trench gate U-shaped (TGU) channel silicon-on-insulator lateral insulated gate bipolar transistor (SOI-LIGBT) is investigated and novel structures are proposed for the first time with numerical simulation in this article. The TGU SOI-LIGBT features two U-shaped trench gates, G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> and G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , connected together. The U-shaped trench for G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> serves as a hole barrier trench. A large number of holes accumulate in the U-shaped region during the turn-on transient because of the U-shaped architecture and the hole-blocking effect of G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . The displacement current induced by the nonuniform distributed holes overcharges the gate and leads to high di/dt. In this article, the novel structures (Novel-1 and Novel-2) with G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> partially filled by the polysilicon are proposed for the improvement in gate voltage overshoot while keeping superior turn-on loss ( E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> ON</sub> ). The novel structures (Novel-1 and Novel-2) can suppress the hole accumulation and slow down the rising of the electric potential in the silicon region near the G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . The di/dt can be lowered and the displacement current that overcharges G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> can be effectively shielded. Compared with the conventional TGU structure, the di/dt of the Novel-2 are improved by 56.3% at the same E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> ON</sub> of 2.4 mJ/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Reducing the polarization mismatch between the last quantum barrier and p-EBL to enhance the carrier injection for AlGaN-based DUV LEDs

In this work, we report an AlGaN-based ∼275 nm deep ultraviolet light-emitting diode (DUV LED) that has AlGaN based quantum barriers with a properly large Al composition. It is known that the increased conduction band barrier height helps to enhance the electron concentration in the active region. However, we find that the promoted hole injection efficiency is also enabled for the proposed DUV LED when the Al composition increases. This is attributed to the reduced positive polarization charge density at the last quantum barrier (LQB) and p-type electron blocking layer (p-EBL) interface, which can suppress the hole depletion effect in the p-EBL. Thus, the hole concentration in the p-EBL gets promoted, which is very helpful to reduce the hole blocking effect caused by the p-EBL. Therefore, thanks to the improved carrier injection, the proposed DUV LED increases the optical power and reduces the forward voltage when compared with the conventional DUV LED.

Increasing the Carrier Injection Efficiency of GaN-Based Ultraviolet Light-Emitting Diodes by Double Al Composition Gradient Last Quantum Barrier and p-Type Hole Supply Layer

A 365 nm AlxGa1-xN-based ultraviolet light-emitting diodes (LEDs) with double Al composition gradient last quantum barrier and hole supply layer structure has been studied. Experimental results show that the proposed structure enhances the carrier injection efficiency and suppresses the overflow of electrons. The introduction of three-dimensional hole gas further enhances the hole injection efficiency. As a result, the wall plug efficiency and electroluminescence intensity are significantly improved. In addition, the carrier concentration and the radiative recombination rate in the active region of the quantum well increases. Looking at the energy band diagram, one sees that the double Al composition gradient structure leads to higher electron blocking and alleviates the hole blocking effect. Overall, we conclude that the double Al composition gradient structure provides a pathway to achieve high-efficiency ultraviolet LEDs.

A Novel Annealing‐Free Amorphous Inorganic Metal Oxyhydroxide Cathode Interlayer for Efficient and Stable Inverted Perovskite Solar Cells

The state‐of‐the‐art high‐performance perovskite solar cells (PSCs) with inverted p‐i‐n device structure normally use crystalline metal oxide materials or organic small molecules as the cathode interlayer between the fullerene layer and metal electrode. However, these interlayers are made by either high‐temperature or complicated vacuum‐assisted fabrication process, and in many cases, they are not efficient and effective enough to simultaneously extract the electrons and suppress the interfacial charge recombination. Herein, for the first time, a facile low‐temperature solution‐processed strategy is demonstrated to fabricate an amorphous metal oxyhydroxide (a‐MOH) thin film, which is used as a robust cathode interlayer in inverted PSCs. The a‐MOH interlayer not only facilitates electron extraction and collection via “energy‐favorable” electron tunneling, but also suppresses the interfacial charge recombination via effective hole blocking and electron backflow inhibition. As a result, the PSCs based on a‐MOH interlayer achieve a stabilized power conversion efficiency (PCE) of 21.1% and retain 93% of initial PCE after continuous one‐sun illumination for 500 hours.

Vacuum Dual-Source Thermal-Deposited Lead-Free Cs3Cu2I5 Films with High Photoluminescence Quantum Yield for Deep-Blue Light-Emitting Diodes.

Deep-blue emitters are greatly desirable for preparing white light-emitting diodes and enhancing the color gamut of full-color display. The deep-blue lead halide perovskite light-emitting diodes (PeLEDs) exhibit far inferior performance compared to green and red counterparts and suffer from lead toxicity, hampering their applications. Nontoxic, stable, and wide band gap zero-dimensional (0D) Cs3Cu2I5 with relatively high exciton binding energy has great potential as deep-blue emitters. However, the development of PeLEDs remains a huge challenge due to the difficulties in preparing a high-quality Cs3Cu2I5 film and device design, arising from an inherent wide band gap together with deep ionization potential. Here, a continuous and pin-hole-free Cs3Cu2I5 thin film with deep-blue emission centered at 440 nm was prepared by the dual-source thermal evaporation approach, and a high photoluminescence quantum yield of 58% was achieved, corresponding to significant enhancement of 61% compared with that of the Cs3Cu2I5 thin film synthesized by solution processes. Furthermore, saturated deep-blue PeLEDs at the Commission Internationale de L'Eclairage (CIE) coordinates (0.15, 0.08) were obtained by employing an electron-transfer layer composed of a 1,4,5,8,9,11-hexa-azatriphenylene hexacarboni-trile (HAT-CN) and N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)benzidine (NPB) organic heterojunction to realize the effective hole blocking, rendering an external quantum efficiency of approximately 0.1%. These results will be extensively beneficial to wide band gap material and device preparation.

Origin of GaN-InGaN-GaN barriers in enhancing the hole injection for InGaN/GaN green light-emitting diodes

Abstract In this work, we propose to insert an In0.07Ga0.93N layer into the GaN quantum barriers for InGaN/GaN green light-emitting diodes (LEDs) to achieve the enhanced hole injection and improve the internal quantum efficiency (IQE). Nevertheless, we also find that the insertion layer cannot be too thin, and a properly thick insertion layer is recommended, because the polarization induced electric field in the GaN/In0.07Ga0.93N/GaN quantum barriers can accelerate holes, and thereby the hole blocking effect at the GaN/In0.07Ga0.93N interfaces and the increase for the valence band barrier height of p-EBL will be less significant. Other advantage is that the insertion In0.07Ga0.93N layer can also reduce the polarization induced electric field in the quantum wells, which is helpful to increase the radiative recombination rate.

Improving the Efficiency of Multilayer Organic Light‐Emitting Transistors by Exploring the Hole Blocking Effect

AbstractOrganic light‐emitting transistors (OLETs) are emerging as a type of multifunctional devices that integrate the electrical switching and the light‐emitting function. Among the various device structures, multilayer OLETs have shown superior performance due to their flexibility in structure design and material choice. However, multilayer OLETs usually work in the unipolar mode, resulting in extreme unbalance between the holes and electrons, restricting the further improvement of their performance. Here, an investigation of the hole blocking layer (HBL) is presented. The results show that a high electron mobility is not necessarily in a first place when choosing the HBL, while a deeper highest occupied molecular orbital level of the HBL can better facilitate the exciton recombination efficiency. By using bis[(4‐tert‐butylphenyl)‐1,3,4‐oxadiazolyl]phenylene instead of commonly used bathophenanthroline (Bphen) as the HBL, the external quantum efficiency (EQE) is more than doubled for a blue fluorescent OLET, and an EQE as high as 10.3% is achieved in a green phosphorescent OLET with a maximum brightness of ≈8000 cd m−2. The findings in this work highlight the importance of carrier blocking in building high efficiency OLETs and might provide some guidance for their structure design and material choice.

Improving hole injection from p-EBL down to the end of active region by simply playing with polarization effect for AlGaN based DUV light-emitting diodes

In this work, we simply take advantage of the polarization effect to efficiently improve the hole injection from the p-type electron blocking layer (p-EBL) to the end of the active region for AlGaN based deep ultraviolet light emitting diodes (DUV LEDs). By properly increasing the AlN composition of AlGaN quantum barriers, a smaller positive polarized charge density at the last quantum barrier/p-EBL interface can be obtained, which correspondingly leads to the suppressed hole depletion and the reduced hole blocking effect in the p-EBL. Meanwhile, we properly increase the quantum well thickness so that the polarized electric field can even more accelerate the holes, and this will homogenize the hole distribution more across the MQWs. Therefore, the external quantum efficiency for DUV LEDs can be enhanced.

ITO and electron transport layer-free planar perovskite solar cells on transparent Nb-doped anatase TiO2-x electrodes

Here, we reported on planar perovskite solar cells (PSCs) which are free of the indium tin oxide (ITO) and electron transport layer (ETL) directly prepared on Nb-doped TiO2-x (NTO) electrodes. By rapid thermal annealing of NTO film at a temperature of 600 °C under vacuum ambient, we obtained conductive anatase NTO electrodes that act as transparent electrodes and ETL simultaneously in ITO and ETL-free PSCs. The sputtered NTO electrode showed decreasing resistivity with decreasing temperature, indicating metallic conductivity. A planar NTO∖(FAPbI3)1-x(MAPbBr3)x∖Spiro-MeOTAD∖Au cell showed a power conversion efficiency of 12.50% and open-circuit voltage of 1.08 V in spite of the absence of ETL. The ITO and ETL-free PSC with an NTO electrode exhibited a higher open-circuit voltage of 1.08 V than did an ETL-free PSC with ITO electrode because of effective hole blocking by the NTO electrodes. Our results suggest that sputtered NTO film is a promising multi-functional electrode acting as ETL and transparent electrode simultaneously for achieving simply fabricated and cost-effective PSCs.

Photoelectrochemical water splitting by engineered multilayer TiO2/GQDs photoanode with cascade charge transfer structure

Herein, for the first time, an efficient photoanode engineered with the cascade structure of FTO|c-TiO2|few graphene layers|TiO2/GQDs|Ni(OH)2 assembly (Ni(OH)2 photoanode) is designed. This photoanode exhibited much lower electron–hole recombination, fast charge transport, higher visible light harvesting, and excellent performance with respect to FTO|c-TiO2|TiO2 assembly (TiO2 photoanode) in the photoelectrocatalytic oxygen evolution process. The photocurrent density of Ni(OH)2 photoanode is 7 times (0.35 mA cm−2 at 1.23 V vs. RHE) greater than that of TiO2 photoanode (0.045 mA cm−2 at 1.23 V vs. RHE). The compact TiO2 (c-TiO2) layer in Ni(OH)2 photoanode plays a role of an effective hole-blocking layer. Few-layer graphene layer could speed up the transport of the photogenerated electrons from the conduction band of the TiO2/GQDs to FTO. Ni(OH)2 layer could transfer rapidly holes into electrolyte solution.

Desirable TiO2 compact films for nanostructured hybrid solar cells

ABSTRACTTwo different TiO2 compact films, fabricated by sol-gel spin-coating (SC) and spray-pyrolysis (SP) processes, were employed as an electron transport layer (ETL) to the nanostructured hybrid perovskite solar cells (PSCs), and they were comprehensively investigated through the various characterisation approaches using electrochemical and physicochemical approaches. With cyclic voltammetry and XPS results, the absence of pinholes on the SP-TiO2 compact films was indicated, and AFM and SEM results confirmed the SP-TiO2 compact films had lower surface roughness and more compact particle connectivity, offering a decent interface between the perovskite active layer and the adjacent TiO2 films. The performance of the SP-PSCs using the SP-TiO2 compact films was 7.06%, which was 3 times higher than that of the SC-PSCs. Voc decay measurement also confirmed that such pinhole-free and improved film interfaces of SP-TiO2 compact films contributed to elongating electron lifetime in PSCs by the enhanced hole blocking effect of the SP-TiO2 compact films.

Interface‐Modification‐Induced Gradient Energy Band for Highly Efficient CsPbIBr2 Perovskite Solar Cells

AbstractInorganic cesium lead halide perovskite solar cells (PSCs) have received enormous attention due to their excellent stability compared with that of their organic–inorganic counterparts. However, the lack of optimization strategies leads the inorganic PSCs to suffer from low efficiency arising from significant recombination. To overcome this dilemma, a surface modification of the electron transport layer (ETL)/perovskite interface is undertaken by using SmBr3 to improve the crystallization and morphology of the perovskite layer for enhanced ETL/perovskite interface interaction. Encouragingly, a gradient energy band is created at the interface with an outstanding hole blocking effect. As a result, both the charge recombination occurring at the interface and the nonradiative recombination inside the perovskite are suppressed, and, simultaneously, the charge extraction is improved successfully. Therefore, the power conversion efficiency of the CsPbIBr2 PSCs is increased to as high as 10.88% under one sun illumination, which is 30% higher than its counterparts without the modification. It is logically inferred that this valuable optimization strategy can be extended to other analogous structures and materials.

Improved H2-generation performance of Pt/CdS photocatalyst by a dual-function TiO2 mediator for effective electron transfer and hole blocking

Surface modification with noble metal cocatalysts was proved to be a useful route for boosting photocatalytic efficiency of various photocatalysts. Nevertheless, considering the random dispersion of metallic cocatalysts on the photocatalyst surface, the noble metal-loaded photocatalyst generally shows a limited enhancement of its activity because the noble metals can also work as the recombination sites of photoinduced charges. In this paper, TiO2 as a dual-function mediator (for effective electron transport and hole block) is successfully introduced into the interface of Pt and CdS to form PtTiO2/CdS photocatalyst, with an aim of suppressing the high recombination rate of electron-hole pairs on the Pt active sites. Under visible light, all the prepared PtTiO2/CdS displayed distinctly enhanced photocatalytic hydrogen-generation performance and the PtTiO2/CdS(8%) attains the highest photocatalytic H2-production rate (294.2 μmol/h), a value significantly higher than that of Pt/CdS about 3.2 time. A dual-function TiO2-mediated mechanism was put forward to account for the superior hydrogen production of PtTiO2/CdS photocatalyst, namely, the TiO2 layer in the PtTiO2/CdS not only works as electron-transport layers to effectively transfer photogenerated electrons to promote the H2-production reaction on Pt cocatalysts, but also acts as hole-block layer to prevent the possible recombination of photogenerated charges on the Pt active sites, resulting in a distinct improvement of final H2-generation activity.

In-situ facile deposition of TiO2 hole blocking layers for efficient hole-conductor-free perovskite solar cells

A compact hole blocking layer is necessary for high efficient perovskite solar cell, which was usually fabricated by spin coating or spray pyrolysis with the followed annealing process, or vacuum deposition. Here, we deposited TiO2 compact layers by an in-situ room-temperature solvent method, which were applied as an effective hole blocking layer for hole-conductor-free perovskite solar cells with carbon electrodes. The thickness of the TiO2 compact layer can be easily regulated by the depositing time. By optimizing the TiO2 depositing time, the power conversion efficiency of hole-conductor-free perovskite solar cells was up to 10.66%.

Carrier Dynamics Engineering for High-Performance Electron-Transport-Layer-free Perovskite Photovoltaics

Summary Electron-transport-layer-free (ETL-free) device architectures are promising designs for perovskite photovoltaics because they offer simpler configurations, low cost, and convenience for versatile optoelectronics. However, the development of ETL-free photovoltaics is hindered by their low performance. Herein, we reveal that a low electron-injection rate at the ETL-free interface is responsible for the performance loss. Moreover, we demonstrate that improving carrier lifetimes in the perovskite films can remedy the poor carrier extraction at interfaces, enabling carrier collection efficiency in ETL-free photovoltaics to approach that in ETL-containing devices. Using perovskite films with microsecond carrier lifetimes, we obtained ETL-free devices with a power conversion efficiency (PCE) of 19.5%, nearly eliminated hysteresis, and good stability. Such a PCE value is comparable to that (20.7%) of the analogous ETL-containing photovoltaics. These results offer opportunities for ETL-free architecture designs in the perovskite photovoltaics family. More importantly, this research provides a general approach to improving the performance of photovoltaics with low-injection-rate interfaces.