JIANG ZHI XUAN

A formamidinium (FA)‐based quasi‐2D Ruddlesden–Popper (RP) perovskite, namely, (ThMA)₂(FA) _{n −1}Pb _n I_{3 n +1} (nominal n = 5), is successfully demonstrated with high photovoltaic performance by using an organic‐salt‐assisted crystal growth method. The optimized device exhibits a champion efficiency of 19.06%, which is a record for quasi‐2D RP perovskite solar cells with nominal n‐value lower than 6.

Abstract

Quasi‐2D Ruddlesden–Popper (RP) perovskite solar cells (PSCs) have drawn significant attention due to their appealing environmental stability compared to their 3D counterparts. However, the relatively low power conversion efficiency (PCE) greatly limits their applications. Here, high photovoltaic performance is demonstrated for quasi‐2D RP PSCs using 2‐thiophenemethylammonium as spacer with nominal n‐value of 5, which is based on the stoichiometry of the precursors. The incorporation of formamidinium (FA) in quasi‐2D RP perovskites reduces the bandgap and improves the light absorption ability, resulting in enlarged photocurrent and an increased PCE of 16.18%, which is higher than that of reported analogous methylammonium (MA)‐based quasi‐2D PSC (≈15%). A record high PCE of 19.06% is further demonstrated by using an organic salt, namely, 4‐(trifluoromethyl)benzylammonium iodide, assisted crystal growth (OACG) technique, which can induce the crystal growth and orientation, tune the surface energy levels, and suppress the charge recombination losses. More importantly, the devices based on OACG‐processed quasi‐2D RP perovskites show remarkable environmental stability and thermal stability, for example, the PCE retaining ≈96% of its initial value after storage at 80 °C for 576 h, while only ≈37% of the original efficiency left for FAPbI₃‐based

3D PSCs.

By using a solvent‐mediated phase transformation process, a record certified 21.8% power conversion efficiency in pure‐iodide, alkaline‐metal‐free MA_0.5FA_0.5PbI₃ perovskite‐based solar cells is achieved.

Abstract

Composition and film quality of perovskite are crucial for the further improvement of perovskite solar cells (PSCs), including efficiency, reproducibility, and stability. Here, it is demonstrated that by simply mixing 50% of formamidinium (FA⁺) into methylammonium lead iodide (MAPbI₃), a highly crystalline, stable phase, and compact, polycrystalline grain morphology perovskite is formed by using a solvent‐mediated phase transformation process via the synergism of dimethyl sulfoxide and diethyl ether, which shows long carrier lifetime, low trap state density, and a record certified 21.8% power conversion efficiency (PCE) in pure‐iodide, alkaline‐metal‐free MA_0.5FA_0.5PbI₃ perovskite‐based PSCs. These PSCs show very high operational stability, with 85% PCE retention upon 1000 h 1 Sun intensity illumination. A 17.33% PCE module (6.5 × 7 cm²) is also demonstrated, attesting to the scalability of such devices.

Tuning black phosphorus (BP) thickness with a laser: A liquid‐phase exfoliation method assisted by a pulsed laser is described. The layer number and lateral size of few‐lsayered BP nanosheets depends on the laser duration and solvent. This few‐layered BP nanosheets enables the study of the relationship between morphology and BP‐based anode performance, showing thinner thickness and smaller lateral size promote faster Li⁺ transport.

Abstract

Few‐layer black phosphorus (BP) is an emerging 2D material suitable for energy applications. However, its controllable preparation remains challenging. Herein, a highly efficient route is presented for the scalable production of few‐layered BP nanosheets using a pulsed laser in low‐boiling point solvents. Changing the laser irradiation time, energy, and solvent type leads to precise control over the layer number and lateral size of the nanosheets with a narrow distribution. The process is understood by a plasma quenching mechanism and interlayer interaction weakened by the in situ generated vapor bubbles. The excellent control of the BP nanosheets enables morphological effects on Li‐ion battery performance to be studied. Low layer numbers benefit both charge transfer and Li⁺ ion diffusion, while a high aspect ratio can not only improve the charge transfer but also increase the Li⁺ ion diffusion path. This study delivers insights on the tailored fabrication of thin 2D materials using lasers for morphology‐dependent electrochemical energy conversion and storage.

Rapid degradation of ion migration, measurement source‐induced damage, phase transition, and separation of perovskite materials hinder accurate evaluation by conventional characterization tools. Recent advanced characterization tools, such as cryogenic temperature assisted measurement, in situ observation, and multidimensional imaging/mapping are presented here that enable the correct diagnose perovskite properties.

Abstract

In the last 10 years, organic–inorganic hybrid perovskite solar cells have achieved unprecedented advances, to the point where they now exhibit extremely high efficiency. However, long‐term stability and areal scalability limitations impede the commercial application of perovskite materials, and appropriate diagnosistic tools have become necessary to evaluate perovskite materials. Characterization of perovskite materials is regularly misinterpretated, due to unique intrinsic and extrinsic factors: degradation from the measurement source, ion migration, phase transition, and separation. Herein, studies on perovskites are reviewed that have used advanced characterization tools to overcome characterization challenges. Cryogenic temperature assisted measurements mitigate degradation or phase transitions induced by the measurement source. In situ measurements can track the variation of perovskite materials depending on external stimuli. Spatial material properties are able to be evaluated by the use of multidimensional mapping techniques. An overview of these advanced characterization tools that can overcome the challenges associated with established tools provides the opportunity for further understanding perovskite materials and solving the remaining challenges on the road to commercialization.

This article reports the interfacial modification of mixed‐cation (Cs) _x (FA)_{1− x} PbI₃ perovskite films with guanidinium hydroiodide salt, which results in the formation of a low‐dimensional δ‐FAPbI₃‐like phase on the 3D perovskite surface. The presence of this thin layer facilitates charge transfer at interfaces and reduces charge carrier recombination pathways. Consequently, the performance and moisture stability of the control devices is improved compared to the unmodified device.

Abstract

Interfacial engineering between the perovskite and hole transport layers has emerged as an effective way to improve perovskite solar cell (PSC) performance. A variety of organic halide salts are developed to passivate the traps and enhance the charge carrier transport. Here, the use of guanidinium iodide (GuaI) for interfacial modification of mixed‐cation (Cs) _x (FA)_{1− x} PbI₃ perovskite films, which results in the formation of a low‐dimensional δ‐FAPbI₃‐like phase on the 3D perovskite surface, is reported. The presence of this thin layer facilitates charge transfer at interfaces and reduces charge carrier recombination pathways as evidenced by enhanced carrier lifetimes and favorable interfacial band alignment. As a result, the power conversion efficiency of the control device is boosted from 19.22% to 20.07%, mainly due to improved open‐circuit voltage (V _oc) and fill factor. Furthermore, the post‐treatment with GuaI improves the moisture stability of perovskite polycrystalline films and ambient stability of PSCs.

The nonionic polymer with multiple amino groups is introduced to passivate both metal‐ and halide‐induced defects of all‐inorganic CsPbI₂Br perovskite by coordination and hydrogen bonds, simultaneously. Consequently, a well‐controlled grain size, reduced defects, and reinforced phase structure of CsPbI₂Br film are achieved, which boosts the efficiency of perovskite solar cells up to 15.48% with excellent humidity stability.

The all‐inorganic CsPbI₂Br perovskite with superior thermal durability faces challenges of low‐phase stability and high moisture sensitivity. Herein, a nonionic additive of polyethyleneimine (PEI) with multiple amino groups is introduced to form hydrogen bond with I⁻/Br⁻ ions and coordinate with Pb²⁺/Cs⁺ ions simultaneously. The strong interplay between PEI and CsPbI₂Br achieves a well‐controlled grain size, reduced defects, and reinforced phase structure of CsPbI₂Br film, which boosts the power conversion efficiency (PCE) of perovskite solar cells to 15.48%. The hydrophobic long alkyl chain of PEI greatly improves the humidity resistance, retaining 81.9% of initial PCE of zjr unsealed device under 20 ± 5% relative humidity (RH) for 500 h. Remarkably, a PCE of 13.37% is achieved by the device based on CsPbI₂Br–PEI film processed under ambient condition (≈22% RH, ≈25 °C).

Publication date: 17 June 2020

Source: Joule, Volume 4, Issue 6

Author(s): Shengfan Wu, Jie Zhang, Zhen Li, Danjun Liu, Minchao Qin, Sin Hang Cheung, Xinhui Lu, Dangyuan Lei, Shu Kong So, Zonglong Zhu, Alex.K.-Y. Jen

Publication date: 20 May 2020

Source: Joule, Volume 4, Issue 5

Author(s): Yan Jiang, Shih-Chi Yang, Quentin Jeangros, Stefano Pisoni, Thierry Moser, Stephan Buecheler, Ayodhya N. Tiwari, Fan Fu

Publication date: Available online 23 April 2020

Source: Joule

Author(s): Nicole Moody, Samuel Sesena, Dane W. deQuilettes, Benjia Dak Dou, Richard Swartwout, Joseph T. Buchman, Anna Johnson, Udochukwu Eze, Roberto Brenes, Matthew Johnston, Christy L. Haynes, Vladimir Bulović, Moungi G. Bawendi

The technology of pulsed laser irradiation in liquid from a solid target to liquid is pioneered, yielding liquid ternary supranano‐(<10 nm) alloys with a unique core–shell structure. The decoration of such supranano‐alloys as an electron mediator at grain boundaries promotes the electron extraction and transfer of the hybrid perovskite film of a perovskite solar cell and drives the efficiency up to 22.03%.

Abstract

Creating colloids of liquid metal with tailored dimensions has been of technical significance in nano‐electronics while a challenge remains for generating supranano (<10 nm) liquid metal to unravel the mystery of their unconventional functionalities. Present study pioneers the technology of pulsed laser irradiation in liquid from a solid target to liquid, and yields liquid ternary nano‐alloys that are laborious to obtain via wet‐chemistry synthesis. Herein, the significant role of the supranano liquid metal on mediating the electrons at the grain boundaries of perovskite films, which are of significance to influence the carriers recombination and hysteresis in perovskite solar cells, is revealed. Such embedding of supranano liquid metal in perovskite films leads to a cesium‐based ternary perovskite solar cell with stabilized power output of 21.32% at maximum power point tracing. This study can pave a new way of synthesizing multinary supranano alloys for advanced optoelectronic applications.

A low‐temperature crystallization strategy of CsPbIBr₂ perovskite solar cells is reported. The additive n‐butylammonium iodide (BAI) is incorporated into the perovskite precursor to improve crystallinity, optimize morphology, and passivate defects at 160 °C. As a result, a high‐level PCE of 10.78% with a high open‐circuit voltage (V _OC) of 1.25 V is achieved.

Inorganic cesium lead halide perovskite solar cells (PSCs) have been widely explored due to their outstanding thermal stability and photovoltaic performance. However, the application and development of CsPbIBr₂‐based PSCs is still hindered by major challenges such as high fabrication temperature and large voltage loss. To address these difficulties, additive engineering is conducted using n‐butylammonium iodide (BAI). It is found that it not only improves the crystallization and morphology of perovskite layers but also substantially decreases the annealing temperature. In addition, the BAI incorporation decreases trap state density and restrains nonradiative recombination. As such, a high power conversion efficiency (PCE) of 10.78% is achieved, 21% higher compared with that of the control sample (8.88%). It should be noted that this is particularly high for the CsPbIBr₂ PSCs fabricated at low temperatures (<200 °C) that are required for flexible devices based on polymeric substrates.

In article number https://doi.org/10.1002/aenm.2020008232000823, Carr Hoi Yi Ho, Franky So and co‐workers presented a simple yet highly compatible interconnecting layer for organic tandem solar cells. All double‐junction tandem devices with different active layers show high reproducibility and efficiencies in several laboratories. Among these tandem devices, an excellent power conversion efficieny of 16.1% is achieved. In addition, most of the tandem devices achieve more than 40% enhancement from the single‐junction solar cell.

In this article, a forward‐looking perspective is given to develop new approaches for the issues related to lead in hybrid perovskites. The currently used remediation tools for the sanitization of soil and water are described and discussed to transfer these technologies to hybrid perovskite photovoltaic cells. Finally, the impact of lead content is assessed in comparison with existing lead based‐technologies.

Abstract

Hybrid Perovskite (HP) semiconductors have been skyrocketing the field of new generation photovoltaics and expanding into advanced optoelectronics. Perovskite photovoltaics (PV) can give a tremendous push to the green energy transition, which calls for efficient, low cost, but also environmentally friendly solutions. Halide perovskites present a serious drawback related to the presence of toxic materials, i.e., lead, with its associated health and environment concerns. These concerns severely hamper their commercialization. So far, only a few viable alternatives to Pb have been found, which lag behind in terms of power conversion efficiency. Here, a forward‐looking perspective is developed presenting different potential strategies to overcome the environmental and health issues related to the use and release of lead for operative HP solar cells. The possible lead‐leakage paths and related “remediation” tools are reviewed, and possible strategies are collated with a view to beginning a new era of lead containing HP devices. Finally, through a comparison with existing lead‐based technology, a comparative study is presented to provide the tools that are essential for a real evaluation of the impact of lead content on HP commercialization.

An optimal power conversion efficiency (PCE) of 17.4% is achieved in the optimized ternary organic photovoltaics (OPVs) with two well‐compatible acceptors (BTP‐4F‐12 and MeIC) and one wide bandgap donor (PM6), resulting from simultaneously improved J _SC, fill factor (FF), and V _OC. The energy loss of ternary OPVs is minimized compared with the two binary OPVs, which is an important development for PCE improvement of ternary OPVs.

Abstract

A power conversion efficiency (PCE) of 16.2% is achieved in PM6:BTP‐4F‐12 based organic photovoltaics (OPVs). On the basis of efficient binary OPVs, a series of ternary OPVs are constructed by incorporating MeIC as the third component. The open circuit voltages (V _OCs) of ternary OPVs can be gradually increased along with the incorporation of MeIC, suggesting the formation of an alloy state between BTP‐4F‐12 and MeIC with good compatibility. The energy loss (E _loss) of ternary OPVs can be decreased compared with that of two binary OPVs, contributing to the V _OC improvement of ternary OPVs. The short circuit current density (J _SC) and fill factor (FF) of ternary OPVs can also be simultaneously enhanced with MeIC content up to 10 wt% in acceptors, leading to 17.4% PCE of the optimized ternary OPVs. The J _SC and FF improvement of ternary OPVs is thought to result from the optimized ternary active layers with more efficient photon harvesting, exciton dissociation and charge transport. The 17.4% PCE and 79.2% FF is among the top values of ternary OPVs. This work indicates that a ternary strategy is an emerging method to simultaneously minimize E _loss and optimize photon harvesting as well as improve the morphology of active layers for realizing performance improvement for OPVs.

An aryl diammonium iodide: PDMAI is demonstrated first to be highly promising to enhance open‐circuit voltage, short‐circuit current, and stability of FAMAPbI₃ based perovskite solar cells through surface passivation. Theoretical calculation suggests a stronger energy binding between PDMAI and perovskite surface. This work provides a new passivation strategy for efficient and stable perovskite solar cells.

Abstract

Surface passivation is increasingly one of the most prominent strategies to promote the efficiency and stability of perovskite solar cells (PSCs). However, most passivation molecules hinder carrier extraction due to poorly conductive aggregation between perovskite surface and carrier transportation layer. Herein, a novel molecule: p‐phenyl dimethylammonium iodide (PDMAI) with ammonium group on both terminals is introduced, and its passivation effect is systematically investigated. It is found that PDMAI can mitigate defects at the surface and promote carrier extraction from perovskite to the hole transporting layer, leading to a lift of open‐circuit voltage of 40 mV. Profiting from superior PDMAI passivation, the average efficiency of PSCs has been elevated from 19.69% to 20.99%. As demonstrated with density functional theory calculations, PDMAI probably tends to anchor onto the perovskite surface with both NH₃I tails, and enhances the adhesion and contact to perovskite layer. The exposed hydrophobic aryl core protects perovskite against detrimental environmental factors. In addition, the alkyl component between aryl and ammonium groups is demonstrated to be essentially vital in triggering passivation function, which offers the guidance for the design of passivation molecules.

This work reports a compatible strategy to enhance the efficiency of planar n–i–p Sb₂Se₃ solar cells through Sb₂Se₃ surface modification and an architecture with oriented 1D van der Waals material, trigonal selenium (t‐Se). The p‐type t‐Se layer functionally works as a surface passivation and hole transport material. The all‐inorganic device structure enables high efficiency and superb stability.

Abstract

Environmentally benign and potentially cost‐effective Sb₂Se₃ solar cells have drawn much attention by continuously achieving new efficiency records. This article reports a compatible strategy to enhance the efficiency of planar n–i–p Sb₂Se₃ solar cells through Sb₂Se₃ surface modification and an architecture with oriented 1D van der Waals material, trigonal selenium (t‐Se). A seed layer assisted successive close spaced sublimation (CSS) is developed to fabricate highly crystalline Sb₂Se₃ absorbers. It is found that the Sb₂Se₃ absorber exhibits a Se‐deficient surface and negative surface band bending. Reactive Se is innovatively introduced to compensate the surface Se deficiency and form an (101) oriented 1D t‐Se interlayer. The p‐type t‐Se layer promotes a favored band alignment and band bending at the Sb₂Se₃/t‐Se interface, and functionally works as a surface passivation and hole transport material, which significantly suppresses interface recombination and enhances carrier extraction efficiency. An efficiency of 7.45% is obtained in a planar Sb₂Se₃ solar cell in superstrate n–i–p configuration, which is the highest efficiency for planar Sb₂Se₃ solar cells prepared by CSS. The all‐inorganic Sb₂Se₃ solar cell with t‐Se shows superb stability, retaining ≈98% of the initial efficiency after 40 days storage in open air without encapsulation.

A composite consisting of 1D cation‐doped TiO₂ brookite nanorod embedded by 0D fullerene is investigated as a top modification buffer for inverted perovskite photovoltaic (IP‐PV) cells. The resultant IP‐PV displays an efficiency exceeding 22% with a favorable stability. This work opens up more opportunities in expanding the material inventory for charge transfer layer in perovskite solar cells development and application.

Abstract

Simultaneously achieving high efficiency and high durability in perovskite solar cells is a critical step toward the commercialization of this technology. Inverted perovskite photovoltaic (IP‐PV) cells incorporating robust and low levelized‐cost‐of‐energy (LCOE) buffer layers are supposed to be a promising solution to this target. However, insufficient inventory of materials for back‐electrode buffers substantially limits the development of IP‐PV. Herein, a composite consisting of 1D cation‐doped TiO₂ brookite nanorod (NR) embedded by 0D fullerene is investigated as a top modification buffer for IP‐PV. The cathode buffer is constructed by introducing fullerene to fill the interstitial space of the TiO₂ NR matrix. Meanwhile, cations of transition metal Co or Fe are doped into the TiO₂ NR to further tune the electronic property. Such a top buffer exhibits multifold advantages, including improved film uniformity, enhanced electron extraction and transfer ability, better energy level matching with perovskite, and stronger moisture resistance. Correspondingly, the resultant IP‐PV displays an efficiency exceeding 22% with a 22‐fold prolonged working lifetime. The strategy not only provides an essential addition to the material inventory for top electron buffers by introducing the 0D:1D composite concept, but also opens a new avenue to optimize perovskite PVs with desirable properties.

A composite consisting of 1D cation‐doped TiO₂ brookite nanorod embedded by 0D fullerene is investigated as a top modification buffer for inverted perovskite photovoltaic (IP‐PV) cells. The resultant IP‐PV displays an efficiency exceeding 22% with a favorable stability. This work opens up more opportunities in expanding the material inventory for charge transfer layer in perovskite solar cells development and application.

Abstract

Simultaneously achieving high efficiency and high durability in perovskite solar cells is a critical step toward the commercialization of this technology. Inverted perovskite photovoltaic (IP‐PV) cells incorporating robust and low levelized‐cost‐of‐energy (LCOE) buffer layers are supposed to be a promising solution to this target. However, insufficient inventory of materials for back‐electrode buffers substantially limits the development of IP‐PV. Herein, a composite consisting of 1D cation‐doped TiO₂ brookite nanorod (NR) embedded by 0D fullerene is investigated as a top modification buffer for IP‐PV. The cathode buffer is constructed by introducing fullerene to fill the interstitial space of the TiO₂ NR matrix. Meanwhile, cations of transition metal Co or Fe are doped into the TiO₂ NR to further tune the electronic property. Such a top buffer exhibits multifold advantages, including improved film uniformity, enhanced electron extraction and transfer ability, better energy level matching with perovskite, and stronger moisture resistance. Correspondingly, the resultant IP‐PV displays an efficiency exceeding 22% with a 22‐fold prolonged working lifetime. The strategy not only provides an essential addition to the material inventory for top electron buffers by introducing the 0D:1D composite concept, but also opens a new avenue to optimize perovskite PVs with desirable properties.

The salt of the cation (Mes₂B⁺; Mes: mesitylene) and the anion [B(C₆F₅)₄]⁻ is introduced as superior p‐type dopant for organic semiconductors. The doping mechanism involves electron transfer from the semiconductor to Mes₂B⁺, and the positive charge is stabilized by [B(C₆F₅)₄]⁻. For poly(3‐hexylthiophene), the anion even stabilizes bipolarons. The effective electron affinity of Mes₂B⁺[B(C₆F₅)₄]⁻ is estimated to be 5.9 eV.

Abstract

Molecular doping allows enhancement and precise control of electrical properties of organic semiconductors, and is thus of central technological relevance for organic (opto‐) electronics. Beyond single‐component molecular electron acceptors and donors, organic salts have recently emerged as a promising class of dopants. However, the pertinent fundamental understanding of doping mechanisms and doping capabilities is limited. Here, the unique capabilities of the salt consisting of a borinium cation (Mes₂B⁺; Mes: mesitylene) and the tetrakis(penta‐fluorophenyl)borate anion [B(C₆F₅)₄]⁻ is demonstrated as p‐type dopant for polymer semiconductors. With a range of experimental methods, the doping mechanism is identified to comprise electron transfer from the polymer to Mes₂B⁺, and the positive charge on the polymer is stabilized by [B(C₆F₅)₄]⁻. Notably, the former salt cation leaves during processing and is not present in films. The anion [B(C₆F₅)₄]⁻ even enables the stabilization of polarons and bipolarons in poly(3‐hexylthiophene), not yet achieved with other molecular dopants. From doping studies with high ionization energy polymer semiconductors, the effective electron affinity of Mes₂B⁺[B(C₆F₅)₄]⁻ is estimated to be an impressive 5.9 eV. This significantly extends the parameter space for doping of polymer semiconductors.

Nature Chemistry, Published online: 06 July 2020; doi:10.1038/s41557-020-0488-2

The strength of electrostatic interactions in semiconductors strongly affects their performance in optoelectronic devices. Now, doping two-dimensional naphthalene-based lead halide perovskites with tetrachloro-1,2-benzoquinone has been shown to introduce donor–acceptor interactions within the organic network, without disrupting the inorganic sublattice. This in turn altered the energy of the materials’ electron–hole electrostatic Coulomb interactions.

An optimal power conversion efficiency (PCE) of 17.4% is achieved in the optimized ternary organic photovoltaics (OPVs) with two well‐compatible acceptors (BTP‐4F‐12 and MeIC) and one wide bandgap donor (PM6), resulting from simultaneously improved J _SC, fill factor (FF), and V _OC. The energy loss of ternary OPVs is minimized compared with the two binary OPVs, which is an important development for PCE improvement of ternary OPVs.

Abstract

A power conversion efficiency (PCE) of 16.2% is achieved in PM6:BTP‐4F‐12 based organic photovoltaics (OPVs). On the basis of efficient binary OPVs, a series of ternary OPVs are constructed by incorporating MeIC as the third component. The open circuit voltages (V _OCs) of ternary OPVs can be gradually increased along with the incorporation of MeIC, suggesting the formation of an alloy state between BTP‐4F‐12 and MeIC with good compatibility. The energy loss (E _loss) of ternary OPVs can be decreased compared with that of two binary OPVs, contributing to the V _OC improvement of ternary OPVs. The short circuit current density (J _SC) and fill factor (FF) of ternary OPVs can also be simultaneously enhanced with MeIC content up to 10 wt% in acceptors, leading to 17.4% PCE of the optimized ternary OPVs. The J _SC and FF improvement of ternary OPVs is thought to result from the optimized ternary active layers with more efficient photon harvesting, exciton dissociation and charge transport. The 17.4% PCE and 79.2% FF is among the top values of ternary OPVs. This work indicates that a ternary strategy is an emerging method to simultaneously minimize E _loss and optimize photon harvesting as well as improve the morphology of active layers for realizing performance improvement for OPVs.

A small molecule of 4,4′,4″,4′″‐(pyrazine‐2,3,5,6‐tetrayl) tetrakis (N,N‐bis(4‐methoxyphenyl) aniline) (PT‐TPA) is applied to effectively p‐dope the FA _x MA_{1− x} PbI₃ (FA:HC(NH₂)₂; MA:CH₃NH₃) perovskite surface, with obvious conductivity and carrier concentration increase. After applying PT‐TPA into perovskite solar cells, the doping‐induced band bending at the perovskite surface facilitates hole extraction to the hole‐transport layer and expels electrons toward the cathode, which reduces surface charge recombination. The optimized devices demonstrate a stabilized efficiency of 22.9%.

Abstract

Tailoring the doping of semiconductors in heterojunction solar cells shows tremendous success in enhancing the performance of many types of inorganic solar cells, while it is found challenging in perovskite solar cells because of the difficulty in doping perovskites in a controllable way. Here, a small molecule of 4,4′,4″,4″′‐(pyrazine‐2,3,5,6‐tetrayl) tetrakis (N,N‐bis(4‐methoxyphenyl) aniline) (PT‐TPA) which can effectively p‐dope the surface of FA _x MA_{1− x} PbI₃ (FA: HC(NH₂)₂; MA: CH₃NH₃) perovskite films is reported. The intermolecular charge transfer property of PT‐TPA forms a stabilized resonance structure to accept electrons from perovskites. The doping effect increases perovskite dark conductivity and carrier concentration by up to 4737 times. Computation shows that electrons in the first two layers of octahedral cages in perovskites are transferred to PT‐TPA. After applying PT‐TPA into perovskite solar cells, the doping‐induced band bending in perovskite effectively facilitates hole extraction to hole transport layer and expels electrons toward cathode side, which reduces the charge recombination there. The optimized devices demonstrate an increased photovoltage from 1.12 to 1.17 V and an efficiency of 23.4% from photocurrent scanning with a stabilized efficiency of 22.9%. The findings demonstrate that molecular doping is an effective route to control the interfacial charge recombination in perovskite solar cells which is in complimentary to broadly applied defect passivation techniques.