Chen Weijie

Highly efficient hole transport layer-free low bandgap mixed Pb–Sn perovskite solar cells are realized using a binary additive system composed of CuSCN and GlyHCl. The improved charge transport and suppressed nonradiative recombination across the hole extractive interface have a marked impact on device performance, achieving the highest efficiency reported to date of 20.1%.

Abstract

The development of high-performance hole transport layer (HTL)-free perovskite solar cells (PSCs) with a simplified device structure has been a major goal in the commercialization of PSCs due to the economic advantage of low manufacturing cost. Unfortunately, low bandgap (E _g) mixed Pb–Sn perovskites, which have promising utility for constructing efficient all-perovskite tandem solar cells, have rarely been explored in simplified HTL-free device configurations. In this study, efficient band bending and defect engineering at the interface between perovskite and indium tin oxide (ITO) are realized via a binary additive system using copper thiocyanate (CuSCN) and glycine hydrochloride (GlyHCl). Using mixed Pb–Sn perovskites decorated with crystalline p-type CuSCN, the energy level alignment at the hole extractive interface is modulated in favor of hole extraction, simultaneously increasing hole mobility. Suppressed nonradiative carrier recombination in the perovskite bulk, or across the charge extractive interface, is further achieved by GlyHCl without disturbing the efficient hole transfer characteristics. Notably, a more optimized band alignment is achieved at the hole extractive interface with the addition of GlyHCl. The HTL-free mixed Pb–Sn PSC shows an efficiency up to 20.1% under forward bias with negligible hysteresis, comparable to state-of-the-art high-performance full-structured mixed Pb–Sn PSCs.

Cs₂Pb(SCN)₂Br₂, an all-inorganic pseudo-halide 2D phase perovskite single crystal, is grown by an antisolvent vapor-assisted crystallization method at room temperature. It exhibits a reversible first-order phase transformation to CsPbBr₃ at 450 K. Cs₂Pb(SCN)₂Br₂ has a low exciton binding energy (160 meV). The demonstrated photodetector produces respectable responsivity (8.46 mA W⁻¹) and detectivity (1.2 × 10¹⁰ Jones) at 0.5 V.

Abstract

Most of the reported 2D Ruddlesden–Popper (RP) lead halide perovskites with the general formula of A _{n +1}B _n X_{3 n +1} (n = 1, 2, …) comprise layered perovskites separated by A-site-substituted organic spacers. To date, only a small number of X-site-substituted RP perovskites have been reported. Herein, the first inorganic-cation pseudohalide 2D phase perovskite single crystal, Cs₂Pb(SCN)₂Br₂, is reported. It is synthesized by the antisolvent vapor-assisted crystallization (AVC) method at room temperature. It exhibits a standard single-layer (n = 1) Ruddlesden–Popper structure described in space group of Pmmn (#59) and has a small separation (d = 1.69 Å) between the perovskite layers. The SCN⁻ anions are found to bend the 2D Pb(SCN)₂Br₂ framework slightly into a kite-shaped octahedron, limiting the formation of a quasi-2D perovskite structure (n > 1). This 2D single crystal exhibits a reversible first-order phase transformation to 3D CsPbBr₃ (Pm3m #221) at 450 K. It has a low exciton binding energy of 160 meV—one of the lowest for 2D perovskites (n = 1). A Cs₂Pb(SCN)₂Br₂-single-crystal photodetector is demonstrated with respectable responsivity of 8.46 mA W⁻¹ and detectivity of ≈1.2 × 10¹⁰ Jones at a low bias voltage of 0.5 V.

This review presents state-of-the-art developments in 2D/3D heterostructure perovskite solar cells (PSCs) using surface passivation. The basic crystal structure, surface passivation strategy/process, optoelectronic properties, enhanced stability, and outstanding performance based on 2D/3D PSCs are systematically discussed. In addition, some emerging challenges and critical thoughts for 2D/3D PSCs are proposed to provide insights into follow-up studies.

Abstract

3D perovskite solar cells (PSCs) have shown great promise for use in next-generation photovoltaic devices. However, some challenges need to be addressed before their commercial production, such as enormous defects formed on the surface, which result in severe SRH recombination, and inadequate material interplay between the composition, leading to thermal-, moisture-, and light-induced degradation. 2D perovskites, in which the organic layer functions as a protective barrier to block the erosion of moisture or ions, have recently emerged and attracted increasing attention because they exhibit significant robustness. Inspired by this, surface passivation by employing 2D perovskites deposited on the top of 3D counterparts has triggered a new wave of research to simultaneously achieve higher efficiency and stability. Herein, we exploited a vast amount of literature to comprehensively summarize the recent progress on 2D/3D heterostructure PSCs using surface passivation. The review begins with an introduction of the crystal structure, followed by the advantages of the combination of 2D and 3D perovskites. Then, the surface passivation strategies, optoelectronic properties, enhanced stability, and photovoltaic performance of 2D/3D PSCs are systematically discussed. Finally, the perspectives of passivation techniques using 2D perovskites to offer insight into further improved photovoltaic performance in the future are proposed.

Photoelectrochemical water splitting to hydrogen is a clean process that can achieve green hydrogen. Herein, highly efficient unassisted solar water-splitting devices based on perovskite/silicon tandem solar cells protected by high-transmittance and chemical stability quartz glass are presented, which exhibit a solar–to-hydrogen efficiency of 19.68%.

Photoelectrochemical (PEC) water splitting to hydrogen is a clean process that can achieve green hydrogen. However, the integrated PEC devices have some problems, such as serious incident light loss, poor stability, and high cost. Here, the low-cost perovskite/silicon tandem cell instead of the costly III−V tandem cell as the light absorber is used, combined with high-transmittance quartz glass as a protective layer forming an unassisted solar water-splitting device. Quartz glass can minimize incident light loss and prevent electrolyte corrosion of solar cells. A solar-to-hydrogen efficiency of 19.68% is achieved, and the performance can be maintained for 20 h without noticeable change. This structure design provides a novel integrated solar water-splitting system.

Anchoring acetylcholine on the surface of a perovskite film regulates the band-edge state near the valence band maximum of the surface and inhibits the migration of halogen ions. Consequently, the voltage loss and stability of corresponding perovskite solar cells are greatly improved, suggesting a new direction toward their further commercialization.

Abstract

Although incorporating multiple halogen (bromine) anions and alkali (rubidium) cations can improve the open-circuit voltage (V _oc) of perovskite solar cells (PSCs), severe voltage loss and poor stability have remained pivotal limitations to their further commercialization. In this study, acetylcholine (ACh⁺) is anchored to the surface of a quadruple-cation perovskite to provide additional electron states near the valence band maximum of the perovskite surface, thereby enhancing the band alignment and minimizing the V _oc loss significantly. Moreover, the quaternary ammonium and carbonyl units of ACh⁺ passivate the antisite and vacancy defects of the organic/inorganic hybrid perovskite. Because of strong interactions between ACh⁺ and the perovskite, the formation of lead clusters and the migration of halogen anions in the perovskite film are suppressed. As a result, the device prepared with ACh⁺ post-treatment delivers a power conversion efficiency (PCE) (21.56%) and a value of V _oc (1.21 V) that are much higher than those of the pristine device, along with a twofold decrease in the hysteresis index. After storage for 720 h in humid air, the device subjected to ACh⁺ treatment maintained 70% of its initial PCE. Thus, post-treatment with ACh⁺ appears to be a useful strategy for preparing efficient and stable PSCs.

This study reports on novel solution-processed fullerene derivatives, namely indene-C60-propionic acid butyl ester and indene-C60-propionic acid hexyl ester, as the interlayers in narrow-bandgap perovskite solar cells as well as tandem solar cells. Their effects on the performance and non-radiative recombination in the devices are systematically studied.

Abstract

Interfacial engineering is the key to high-performance perovskite solar cells (PSCs). While a wide range of fullerene interlayers are investigated for Pb-based counterparts with a bandgap of >1.5 eV, the role of fullerene interlayers is barely investigated in Sn-Pb mixed narrow-bandgap (NBG) PSCs. In this work, two novel solution-processed fullerene derivatives are investigated, namely indene-C60-propionic acid butyl ester and indene-C60-propionic acid hexyl ester (IPH), as the interlayers in NBG PSCs. It is found that the devices with IPH-interlayer show the highest performance with a remarkable short-circuit current density of 30.7 mA cm⁻² and a low deficit in open-circuit voltage. The reduction in voltage deficit down to 0.43 V is attributed to reduced non-radiative recombination that the authors attribute to two aspects: 1) a higher conduction band offset of ≈0.2 eV (>0 eV) that hampers charge-carrier-back-transfer recombination; 2) a decrease in trap density at the perovskite/interlayer/C₆₀ interfaces that results in reduced trap-assisted recombination. In addition, incorporating the IPH interlayer enhances charge extraction within the devices that results in considerable enhancement in short-circuit current density. Using a NBG device with an IPH interlayer, a respectable power conversion efficiency of 24.8% is demonstrated in a four-terminal all-perovskite tandem solar cell.

Large organic piperazine cations are incorperated into 3D FASnI₃ lattice to form a FA_{1 − 2 y} PZ_{2 y} Sn_{1− y} I₃ (0 ≤ y ≤ 0.25) structure, which effectively suppresses bulk defect formation and guarantees the continuity of [SnI₆] octahedral structures to promote the device photovoltaic performance with reduced bulk defects and unobstructed carrier transport.

Abstract

Despite Sn-based perovskite solar cells (PSCs) prevailing over lead-free candidates, the Sn vacancies (V_Sn) and Sn⁴⁺ defects seriously deteriorate device photovoltaic performance. The presently reported methods can only effectively achieve surface defect passivation, and it is of great challenge and fundamental importance to develop efficient strategy to deal with the intrinsic defects located inside the lattice. Herein, a novel bulk defect suppression strategy is proposed, introducing large organic piperazine cations (PZ²⁺) into the lattice of 3D FASnI₃ perovskite to restrain the generation of bulk defects. The incorporation of PZ²⁺ results in forming a FA_{1−2 y} PZ_{2 y} Sn_{1− y} I₃ (0 ≤ y ≤ 0.25) structure with no reduction in dimensionality, which guarantees the continuity of [SnI₆] octahedral structures with unobstructed carrier transport and reduced charged defects. The potent interactions between PZ²⁺ and [SnI₆] structures enhance V_Sn formation energy and effectively suppress bulk defect formation. As a result, the FASnI₃+1%PZ films exhibit optimized crystalline quality, decreased background carrier density, lower p-type self-doping, and reduced trap state density. Benefiting from the above advantages, the FASnI₃+1%PZ device achieves an optimal PCE of 9.15% and unencapsulated device maintains over 95% of initial PCE after aging for 1000 h in N₂ golvebox. The bulk defect suppression strategy provides fire-new building bricks toward high-performance Sn-based PSCs.

Acetic acid (HAc) is first introduced to reduce the supersaturated concentration of the precursor solution to form pre-nucleation clusters, thus inducing rapid nucleation. In particular, the introduction of HAc can inhibit the oxidation of Sn²⁺ and reduce the loss of I^-. HAc-assisted device deliver a champion efficiency of 12.26%, maintaining ≈90% of initial efficiency after storage in nitrogen over 3000 h.

Abstract

Tin-based halide perovskites attract incremental attention due to the favorable optoelectronic properties and ideal bandgaps. However, the poor crystalline quality is still the biggest challenge for further progress in tin-based perovskite solar cells (PVSCs) due to the unfavorable defects and uncontrollable crystallization kinetics. Here, acetic acid (HAc) is first introduced to reduce the supersaturated concentration of the precursor solution to preferentially form pre-nucleation clusters, thus inducing rapid nucleation for effective regulation of crystallization kinetics. In particular, the hydrogen ion and acetate ion contained in HAc can effectively inhibit the oxidation of Sn²⁺, and the hydrogen bonding interaction between HAc and iodide ion (I^-) greatly reduces the loss of I^-, which guarantees the I^-/Sn²⁺ stoichiometric ratio of the corresponding perovskite film close to theoretical value, thus effectively reducing the defect density and maintaining the perfect crystal lattice. Consequently, the HAc-assisted tin-based PVSCs achieve a champion power conversion efficiency of 12.26% with superior open-circuit voltage up to 0.75 V. Moreover, the unencapsulated device maintains nearly 90% of the initial PCE even after 3000 h storage in nitrogen atmosphere. This demonstrated strategy enables to prepare high-quality tin-based perovskite film with lower defect density and lattice distortion.

A new design strategy for exploring colloidal quantum dot (CQD)/polymer interfaces is proposed: an additional interfacial layer is incorporated between the CQD/polymer bilayer structures. The interfacial layer between CQD and polymer reduces the localized charge accumulation, suppressing bimolecular recombination. The optimized hybrid devices show a maximum power conversion efficiency of 13.74% and retains over 90% of its initial performance for 402 days under ambient condition without any treatment.

Abstract

Emerging semiconducting materials including colloidal quantum dots (CQDs) and organic molecules have unique photovoltaic properties, and their hybridization can result in synergistic effects for high performance. For realizing the full potential of CQD/organic hybrid devices, controlling interfacial properties between the CQD and organic matter is crucial. Here, the electronic band between the CQD and the polymer layers is carefully modulated by inserting an interfacial layer treated with several types of ligands. The interfacial layer provides a cascading conduction band offset (ΔE _C), and reduces local charge accumulation at CQD/polymer interfaces, thereby suppressing bimolecular recombination; a thin thiol-treated interfacial layer (≈6 nm) decreases shallow traps, resulting in higher short-circuit current (J _SC) and fill factor of hybrid solar cells. Based on these results, a high performance CQD/polymer hybrid solar cell is introduced that demonstrates a power conversion efficiency of 13.74% under AM 1.5 solar illumination. The hybrid device retains more than 90% of its initial performance after 402 days under ambient conditions.

Herein, a low-dimensional intermediate-assisted growth (LDIAG) method is reported to deposit high quality CsPbI₂Br film in ambient atmosphere by introducing imidazolium halide to control both nucleation and growth kinetics. The obtained CsPbI₂Br solar cell shows an efficiency of 17.26% and excellent long-term stability with ≈86% of its initial efficiency retained after being exposed to the ambient environment for 1000 h.

Abstract

Inorganic CsPbI₂Br perovskite is promising for solar cell applications due to its excellent thermal stability and optoelectronic characteristics. Unfortunately, the current high-efficiency CsPbI₂Br perovskite solar cells (PSCs) are mostly fabricated in an inert atmosphere due to their instability to moisture. Herein, a low-dimensional intermediate-assisted growth (LDIAG) method is reported for the deposition of CsPbI₂Br film in ambient atmosphere by introducing imidazole halide (IMX: IMI and IMBr) into the precursor solution to control both nucleation and growth kinetics. The IMX first combines with PbI₂ in the precursor film to form a 2D intermediate which then gradually releases PbI₂ to slowly form high-quality CsPbI₂Br film during annealing. It is found that the LDIAG method produces a uniform, highly crystalline, pinhole-free, and stable CsPbI₂Br film with low defect density. Consequently, the solar cell efficiency is increased to as high as 17.26%, one of the highest for this type of device. Furthermore, the bare device without any encapsulation shows excellent long-term stability with ≈86% of its initial efficiency retained after being exposed to the ambient environment for 1000 h. This work provides a perspective to tune the intermediate phases and crystallization pathway for high-performance inorganic PSCs formed under ambient conditions.

Herein, a scalable and high-performance silver electrode that can serve as a printable replacement to evaporated silver electrodes commonly used in literature is presented. Devices with newly developed electrodes achieve almost the same power conversion efficiencies as evaporated ones. Higher shunt resistances than their vacuum counterparts are also observed and thus perform significantly better under low light conditions.

One of the issues that have caused a wide performance gap between commercially available organic photovoltaic (OPV) modules and the hero cells in literature lies in the lack of printable and roll-to-roll process compatible high-performance top electrodes. This work takes an unorthodox approach to this issue by developing a printable silver nanoparticle (AgNP) film top electrode that can achieve a similar performance as evaporated ones (EvapAg). It illustrates the developmental process from ink formulation to the critical processing conditions that are tailored for OPV devices procedurally. The resultant cells and modules with AgNP electrodes have achieved almost the same power conversion efficiencies (≈90%) as those with evaporated silver electrodes, as demonstrated for multiple material systems, printing methods, as well as layouts. Under low light condition, AgNP cells perform even significantly better than EvapAg ones, due to their lower leakage currents. More importantly, this work has demonstrated that fully printed OPV modules can achieve similar performance as small scale OPV cells with evaporated electrodes when both the electrical and optical performance of their top electrodes are comparable. With the latest generation of materials, this approach offers an attractive alternative for manufacturing of highly efficient OPV modules at large scale.

Interfacial modification is a universal way to improve the device performance of perovskite solar cells (PSCs). However, the effect of ending groups in non-fullerene acceptors (NFAs) for interfacial passivation is still under investigation. Herein, ending groups in NFAs are found to be important in interfacial modification. The findings of this work could provide insights into designing passivation materials for high efficiency PSCs.

The defects in organic–inorganic halide perovskite films are detrimental to device efficiency and the stability of perovskite solar cells (PSCs). Interfacial modification is a universal way to passivate defects and improve device performance. However, the effect of terminal groups in non-fullerene acceptors (NFAs) on interfacial passivation in PSCs is still under investigation. Here, we demonstrate that ending groups of NFAs play an important role in interfacial modification. By comparing four different non-fullerene molecules with different ending groups (ITCC, ITIC, IT-M, IT-4F) applied as passivation layer, we found that devices with ITCC showed better performance, which was attributed to the assistance of the S atom in the ending group of ITCC enhancing adsorption to the perovskite surface compared to the ITIC case, leading to a tighter contact with the perovskite layer and better charge transfer. As a result, in FA_0.85MA_0.15Pb(I_0.85Br_0.15)₃ based PSCs, we achieved a power conversion efficiency of 21.21% and an open-circuit voltage of 1.15 V. Meanwhile, the device with ITCC showed extraordinary stability, maintaining more than 90% initial efficiency after 2000 h. The findings of this work could provide deeper insights into designing novel passivation materials at molecular scale for high efficiency and stable PSCs.

Herein, we probe that oxide thin films grown by atomic layer deposition (ALD) at low temperatures are efficient electron-transporting layers for co-evaporated perovskite solar cells (PSCs). The PSCs achieved power conversion efficiencies above 19%. We show that the low-temperature processed ALD SnO₂ is very promising for flexible and large-area PSCs and mini-modules.

In this work, we explore the potentials and the characteristics of electron-transporting layers (ETL) grown by atomic layer deposition (ALD) at low temperature in co-evaporated perovskite solar cells (PSCs). The thermal-based ALD process has been investigated by tuning the main growing conditions as the number of cycles and the growth temperature. We show that un-annealed ALD-SnO₂ thin films grown at temperatures between 80 °C and 100 °C are efficient ETL in n.i.p co-evaporated MAPbI₃ PSCs which can achieve power conversion efficiencies (PCEs) consistently above 18%. Moreover, the champion PSC achieved a PCE of 19.30% at 120 °C with 150 cycles. We show that the low-temperature processed ALD SnO₂ is very promising for flexible, large-area PSCs and mini-modules. We also report the first co-evaporated PSCs employing low temperature processed ALD ZnO with PCEs approaching 18%. This work demonstrates the potential of the low-temperature ALD deposition method as a potential route to fabricate efficient PSCs at low temperatures.

Microwave irradiation allows a quick low-temperature crystallization of nickel oxide within minutes. Moreover, the doping of In and Sn metal ions diffused from the indium tin oxide layer takes place, leading to unique chemical compositions. The perovskite solar cells with the microwave-annealed nickel oxides show better photovoltaic performances.

Solution-processed nickel oxide (NiO _x ) requires high temperatures (≈300 °C) and a long time (up to 1 h) to crystallize from precursors. Herein, thin films of NiO _x are successfully crystallized at significantly low processing temperatures of ≈130 °C within a few minutes utilizing microwave irradiation. Microwave-annealed NiO _x (MWA-NiO _x ) shows high electrical conductivity and transmittance comparable with those of conventional thermally annealed NiO _x (CTA-NiO _x ). NiO _x crystallization occurs by ohmic heating mechanisms in the indium tin oxide layer, which simultaneously facilitates the diffusion of In and Sn metal cations into the NiO _x layer. Consequently, the chemical composition in the MWA-NiO _x layer shows that both Ni²⁺ and Ni^>3+ species are reduced, which is infeasible with CTA processes, where a decrease in one species necessitates an increase in another. MWA-NiO _x is incorporated as a hole transport layer in triple-cation perovskite (Cs_0.05(MA_0.17FA_0.83)_0.95Pb(I_0.83Br_0.17)₃)-based solar cells. The short-circuit current and open-circuit voltage are enhanced compared with those of CTA-NiO _x devices owing to the combined effects of enhanced conductivity, reduced Ni^>3+ composition, and better energy-level alignment. This proposed crystallization technique of using microwave irradiation could be an effective alternative to conventional processes in improving the suitability of NiO _x for optoelectronic applications.

Perovskite solar cells deliver high efficiencies, but are often made from high-cost bespoke chemicals, such as the archetypical hole-conductor, 2,2′,7,7′-tetrakis(N,N-di-p-methoxy-phenylamine)-9-9′-spirobifluorene, spiro-OMeTAD. In this work, new charge-transporting carbazole-based enamine molecules are reported.

Perovskite solar cells deliver high efficiencies, but are often made from high-cost bespoke chemicals, such as the archetypical hole-conductor, 2,2′,7,7′-tetrakis(N,N-di-p-methoxy-phenylamine)-9-9′-spirobifluorene (spiro-OMeTAD). Herein, new charge-transporting carbazole-based enamine molecules are reported. The new hole conductors do not require chemical oxidation to reach high power conversion efficiencies (PCEs) when employed in n-type-intrinsic-p-type perovskite solar cells; thus, reducing the risk of moisture degrading the perovskite layer through the hydrophilicity of oxidizing additives that are typically used with conventional hole conductors. Devices made with these new undoped carbazole-based enamines achieve comparable PCEs to those employing doped spiro-OMeTAD, and greatly enhanced stability under 85 °C thermal aging; maintaining 83% of their peak efficiency after 1000 h, compared with spiro-OMeTAD-based devices that degrade to 26% of the peak PCE within 24 h. Furthermore, the carbazole-based enamines can be synthesized without the use of organometallic catalysts and complicated purification techniques, lowering the material cost by one order of magnitude compared with spiro-OMeTAD. As a result, we calculate that the overall manufacturing costs of future photovoltaic (PV) modules are reduced, making the levelized cost of electricity competitive with silicon PV modules.

A conjugated polyelectrolyte, TPAFS-TMA is synthesized based on rational molecular design for a hole transport layer (HTL) in perovskite solar cells (PeSCs). The excellent compatibility and well-matched energy levels with perovskite, pH-neutral, semiconducting, optical transparency, and defect passivating properties of TPAFS-TMA suggest its potential as an ideal HTL for large-area PeSCs.

Abstract

π-Conjugated polyelectrolytes (CPEs) have been studied as interlayers on top of a separate hole transport layer (HTL) to improve the wetting, interfacial defect passivation, and crystal growth of perovskites. However, very few CPE-based HTLs have been reported without rational molecular design as ideal HTLs for perovskite solar cells (PeSCs). In this study, the authors synthesize a triphenylamine-based anionic CPE (TPAFS-TMA) as an HTL for p-i-n-type PeSCs. TPAFS-TMA has appropriate frontier molecular orbital (FMO) levels similar to those of the commonly used poly(bis(4-phenyl)-2,4,6-trimethylphenylamine) (PTAA) HTL. The ionic and semiconducting TPAFS-TMA shows high compatibility, high transmittance, appropriate FMO energy levels for hole extraction and electron blocking, as well as defect passivating properties, which are confirmed using various optical and electrical analyses. Thus, the PeSC with the TPAFS-TMA HTL exhibits the best power conversion efficiency (PCE) of 20.86%, which is better than that of the PTAA-based device (PCE of 19.97%). In addition, it exhibits negligible device-to-device variations in its photovoltaic performance, contrary to the device with PTAA. Finally, a large-area PeSC (1 cm²) and mini-module (3 cm²), showing PCEs of 19.46% and 18.41%, respectively, are successfully fabricated. The newly synthesized TPAFS-TMA may suggest its great potential as an HTL for large-area PeSCs.

The phase segregation of mixed-halide perovskite solar cells induces a locally shifted bandgap, hinders the charge-carrier transport, and increases the bulk recombination. By suppressing the phase segregation, the open-circuit voltage is improved from 1.15 to 1.20 V.

Abstract

Wide bandgap (E _g) mixed-halide perovskite has attracted much attention for applications in photovoltaic devices. However, devices featuring this type of perovskite are often subject to a large voltage deficit due to the occurrence of phase segregation, which limits the relevant devices’ access to high performances. Here, the correlation of the phase segregation and voltage losses for wide-E _g mixed-halide perovskite solar cells (PSCs) is clarified by experiments and simulations. Taking 1.67 eV E _g mixed-halide perovskite as an example, it is confirmed experimentally that the control devices produce a poor physical morphology, a locally widened E _g, and an inferior electrical response. By suppressing the phase segregation, the open-circuit voltage (V _oc) can be boosted from 1.15 to 1.20 V, which is a high value for the 1.67 eV E _g mixed-halide PSCs. An electrical simulation of phase segregation reveals that the performance degeneration can be attributed to the bulk recombination due to the energy level mismatch of the varied E _gs. Moreover, a theoretical perspective is produced to expatiate on the strategies for the high V _oc of wide-E _g PSCs. This study brings deep guidance to unlock the potential for high-performance mix-halide PSCs.

Publication date: 15 December 2021

Source: Joule, Volume 5, Issue 12

Author(s): Jiang Liu, Erkan Aydin, Jun Yin, Michele De Bastiani, Furkan H. Isikgor, Atteq Ur Rehman, Emre Yengel, Esma Ugur, George T. Harrison, Mingcong Wang, Yajun Gao, Jafar Iqbal Khan, Maxime Babics, Thomas G. Allen, Anand S. Subbiah, Kaichen Zhu, Xiaopeng Zheng, Wenbo Yan, Fuzong Xu, Michael F. Salvador

A mechanochemical route to prepare stoichiometric-pure and air-stable δ-FAPbI₃ powders is developed, which can be stored for more than 10 months in ambient environment. Redissolving the δ-FAPbI₃ powders can generate a high concentration of large-sized polyiodide colloids, which can serve as nuclei to promote heterogeneous nucleation for perovskite films. As a result, a competitive solar cell efficiency of 24.22% is achieved.

Abstract

A prerequisite for commercializing perovskite photovoltaics is to develop a swift and eco-friendly synthesis route, which guarantees the mass production of halide perovskites in the industry. Herein, a green-solvent-assisted mechanochemical strategy is developed for fast synthesizing a stoichiometric δ-phase formamidinium lead iodide (δ-FAPbI₃) powder, which serves as a high-purity precursor for perovskite film deposition with low defects. The presynthesized δ-FAPbI₃ precursor possesses high concentration of micrometer-sized colloids, which are in favor of preferable crystallization by spontaneous nucleation. The resultant perovskite films own preferred crystal orientations of cubic (100) plane, which is beneficial for superior carrier transport compared to that of the films with isotropic crystal orientations using “mixture of PbI₂ and FAI” as precursors. As a result, high-performance perovskite solar cells with a maximum power conversion efficiency of 24.2% are obtained. Moreover, the δ-FAPbI₃ powder shows superior storage stability for more than 10 months in ambient environment (40 ± 10% relative humidity), being conducive to a facile and practical storage for further commercialization.