JIALINGBO

Residual PbI₂ at the bottom of perovskites can damage the efficiency and stability of fully-textured perovskite/silicon tandem solar cells. Here, a thermal-evaporated CsBr layer is introduced between the perovskite and hole transport layers to interact with residual PbI₂ and construct a gradient perovskite absorber for optimized energy level alignment. Tandem device efficiency of 27.48% and stability in nitrogen over 10 000 h are obtained.

Abstract

The perovskite/silicon tandem solar cell (PK/c-Si TSC) is a reasonable choice that can break through the efficiency limitations of silicon cells. Here, the p-i-n perovskite solar cell is conformally grown by the evaporation–solution combination technique on fully-textured silicon heterojunction cells to realize two-terminal PK/c-Si TSCs. Due to the adverse effect of the residual PbI₂ at the bottom of the perovskite bulk on device performance, a thermal-evaporated CsBr thin layer is introduced between the perovskite layer and the hole transport layer to construct a gradient perovskite absorber for optimized energy level alignment, so as to improve the open-circuit voltage and fill factor of the device. Finally, the PK/c-Si tandem cell achieves an efficiency of 27.48% and is stable in nitrogen over 10 000 h.

The hydrophobic Er@C₈₂ is a bifunctional additive to the 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamino)-9,9′-spirobifluorene (Spiro-OMeTAD) hole transport layer that can enhance the photovoltaic performance and the stability of perovskite solar cells (PSCs) simultaneously.

Perovskite solar cells (PSCs) based on 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamino)-9,9′-spirobifluorene Spiro-OMeTAD hole transport layer (HTL) have achieved a huge success in power conversion efficiency (PCE), but the required lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) dopant in Spiro-OMeTAD HTL is hygroscopic, not only impairing the charge transport but also inducing the instability of PSCs. Herein, Er@C₈₂, which consists of a hydrophobic fullerene cage encapsulating an Er³⁺ ion, is first introduced as a novel additive to modify the Li-TFSI-based Spiro-OMeTAD HTL. By adding a tiny amount of Er@C₈₂ (0.09 mg mL⁻¹) in the Spiro-OMeTAD HTL, the PSC exhibits an efficiency promotion from 17.53% to 19.22%. The PCE enhancement is mainly attributed to the improved film quality of HTL after adding Er@C₈₂, which promotes the oxidation of Spiro-OMeTAD, resulting in faster hole transport and less charge recombination. Simultaneously, the hydrophobic Er@C₈₂ and the improved film quality of HTL lead to a dramatically enhanced stability of PSCs. Accordingly, the Er@C₈₂-modified devices can maintain over 70% and 80% of the initial efficiencies after exposure in air for 400 h and in an Ar atmosphere for 2000 h, respectively. Therefore, this bifunctional Er@C₈₂ additive provides a promising pathway for fabricating highly efficient and stable PSCs.

In this study it is reported an electroluminescent solar cell using CsPbI₃ quantum dots (QDs) via solid-state-ligand exchange process using organic ligand triphenyl phosphite; the device achieves a champion efficiency of 15.21%, and an overall electric power to light conversion efficiency of 3.80% in red light-emitting diode function, a record value for QD photovoltaics.

Abstract

All-inorganic CsPbX₃ (X = Cl, Br, I, or mixed halides) perovskite quantum dots (QDs) exhibit tunable optical bandgaps and narrow emission peaks, which have received worldwide interest in the field of both photovoltaics (PVs) and light-emitting diodes (LEDs). Herein, it is reported a discovery that CsPbI₃ perovskite QD solar cell can simultaneously deliver high PV performance and intense electroluminescence. In specific, the multifunctional CsPbI₃ QD film is fabricated through a simple yet efficient solid-state-ligand exchange process using a tailored organic ligand triphenyl phosphite (TPPI). The function of QD surface manipulation using TPPI here is proven to be twofold, balancing the carrier transport and effectively passivating the QD surface to produce conductive and emissive QD film. The CsPbI₃ perovskite QD solar cell delivers a champion efficiency of 15.21% with improved open circuit voltage and high fill factor. Concurrently functioning as a red LED, the CsPbI₃ perovskite QD solar cell outputs electric power to light conversion efficiency approaching 4%, a record value for QD electroluminescent PVs. The results here indicate that these versatile perovskite QDs may be a promising candidate for fabricating multifunctional optoelectronic devices.

The authors report a novel strategy co-modulation of crystallization and co-passivation of defects for FAPbI₃ perovskite solar cell, which gives a high PCE of 21.6% for the modified PSC (only 16.5% for the control device).

Abstract

Enhancing crystallinity, passivating the grain boundary and interfacial defects have been validated to be critical for improving the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). Herein, a synergetic co-modulation and co-passivation strategy is proposed to simultaneously enhance crystallinity and passivate the grain boundary and surface defects of FAPbI₃ based PSCs. The 4-fluoro-phenethylammonium iodide (4-F-PEAI) added in precursor solution and poly (9-vinylcarbazole) (PVK) added in antisolvent can jointly modulate the crystallization of FAPbI₃ films. The 4-F-PEAI-derived 2D perovskite, which is spontaneously formed at the grain boundaries of FAPbI₃, can passivate the defects effectively. In the meantime, PVK left on top of a FAPbI₃ layer can passivate the surface defects and meanwhile function as an interfacial barrier layer between FAPbI₃ and hole transport layer (HTL) to mitigate the detrimental interfacial charge recombination. With the holistic benefit of the enhanced crystallinity, reduced defects and trap sites, and mitigated non-radiative recombination and suppressed ion migration, the encouraging PCEs up to 21.6% is achieved for the resulting modified PSCs. Additionally, this strategy endows the device with notably enhanced operational stability under continuous exposure to illumination, with more than 84% of the initial PCE being maintained after continuous illumination for 800 h.

Phthalide and 1-Iodooctadecane synergistic optimization successfully passivates cation and anion defects, effectively mitigates carrier non-radiative recombination and consequently results in perovskite solar cells high-efficiency of 22.27% and excellent stability.

Abstract

The carrier non-radiative recombination and instability of device caused by the inherent defects are main factors limiting development of perovskite solar cells (PSCs). During the fabrication process of a PSC device, perovskite films often produce Pb⁰ and I⁰ defects. This paper reports a strategy for synergistic optimization of perovskite films by defects passivation and surface modification. The doping of phthalide (PT) in the Pb-rich (CH(NH₂)₂)_1−x(CH₃NH₃)_xPbI₃ film can passivate lead cation defects, and the modification of 1-iodooctadecane (1-IO) can reduce halogen anion defects and improve stability of PSCs owing to its hydrophobicity. The PT and 1-IO optimized device achieves a power conversion efficiency (PCE) of 22.27%. The optimized PSCs remain 93.2% of the initial PCE when placed in air environment (relative humidity of 10%, 25 °C) more than 70 days. The PT and 1-IO synergistic optimization provides a novel strategy for improving the performance and stability of PSCs.

Recent developments of the quinoxaline-based D–A copolymers for the applications as polymer donor in polymer solar cells and as hole transport material in perovskite solar cells are reviewed.

Abstract

Polymer solar cells (PSCs) have achieved great progress recently, benefiting from the rapid development of narrow bandgap small molecule acceptors and wide bandgap conjugated polymer donors. Among the polymer donors, the D–A copolymers with quinoxaline (Qx) as A-unit have received increasing attention since the report of the low-cost and high-performance D–A copolymer donor based on thiophene D-unit and difluoro-quinoxalline A-unit in 2018. In addition, the weak electron-deficient characteristic and the multiple substitution positions of the Qx unit make it an ideal A-unit in constructing the wide bandgap polymer donors with different functional substitutions. In this review article, recent developments of the Qx-based D–A copolymer donors, including synthetic method of the Qx unit, backbone modulation, side chain optimization, and functional substitution of the Qx-based D–A copolymers, are summarized and discussed. Furthermore, the application of the Qx-based D–A copolymers as hole transport material in perovskite solar cells (pero-SCs) is also introduced. The focus mainly on the molecular design strategies and structure–properties relationship of the Qx-based D–A copolymers, aiming to provide a guideline for developing high-performance Qx-based D–A copolymers for the applications as donor in PSCs and as hole transport material in pero-SCs.

To enhance the photovoltaic performances of perovskite solar cells, an in-depth understanding of recombination processes in full devices is necessary. To gain this insight, transient opto-electronic measurements are applied, revealing that in full devices a superposition of first-, second-, and third-order recombination fully describes the recombination adequately, nonradiative first-order recombination dominating under solar illumination conditions.

Abstract

Ideally, the charge carrier lifetime in a solar cell is limited by the radiative free carrier recombination in the absorber which is a second-order process. Yet, real-life cells suffer from severe nonradiative recombination in the bulk of the absorber, at interfaces, or within other functional layers. Here, the dynamics of photogenerated charge carriers are probed directly in pin-type mixed halide perovskite solar cells with an efficiency >20%, using time-resolved optical absorption spectroscopy and optoelectronic techniques. The charge carrier dynamics in complete devices is fully consistent with a superposition of first-, second-, and third-order recombination processes, with no admixture of recombination pathways with non-integer order. Under solar illumination, recombination in the studied solar cells proceeds predominantly through nonradiative first-order recombination with a lifetime of 250 ns, which competes with second-order free charge recombination which is mostly if not entirely radiative. Results from the transient experiments are further employed to successfully explain the steady-state solar cell properties over a wide range of illumination intensities. It is concluded that improving carrier lifetimes to >3 µs will take perovskite devices into the radiative regime, where their performance will benefit from photon-recycling.

A surface reconstruction strategy is proposed to optimize the surface defect states and crystallization dynamics in an all-inorganic perovskite/organic two-terminal tandem solar cell, leading to efficient hole transport and charge recombination in the interconnecting layer. Finally, a power conversion efficiency of 21.04% and robust operational stability are obtained.

Abstract

The construction of monolithic two-terminal tandem solar cells (2T TSCs) offers the possibility of pursuing high power conversion efficiency (PCE) by overcoming the single-junction Shockley–Queisser limit in photovoltaics. However, little attention is paid to simultaneously improve the stability by utilizing the complementary properties of various photoactive layers. Here, beyond the stacked photoactive layers featuring complementary absorption, all-inorganic perovskite (CsPbI_1.8Br_1.2) is chosen as the photoactive layer of the front wide-bandgap subcell for its intrinsic high thermal stability and ultraviolet (UV)-filtering function to address the burn-in and UV degradation of organic rear subcells. To realize their monolithic integration, the charge recombination efficiency in the interconnecting layer (ICL) between the two types of subcells is tentatively improved by surface reconstruction of all-inorganic perovskite using trimethylammonium chloride. The repaired CsPbI_1.8Br_1.2 surface enables effective suppression of nonradiative recombination and facilitates hole transport, providing efficient charge recombination in the ICL in the 2T TSC. As a result, the all-inorganic perovskite/organic 2T TSC delivers a promising PCE of 21.04%, accompanied by an ultrahigh open-circuit voltage (V _oc) of 2.05 V, which is nearly equal to the superposition of the respective V _oc values of the subcells. More importantly, the 2T TSC simultaneously shows outstanding operational and UV stabilities.

Advanced D-π-D: Two chrysene-based azahelicenes-BA7 and DA6-were constructed and linked with the electron donor bis(9-methyl-9H-carbazol-3-yl)amine (BMCA) to afford D-π-D-type hole-transporting materials for perovskite solar cells. The higher efficiency of the DA6-BMCA-based device may be attributed to its extended S-shaped double helical π-conjugated system.

Abstract

Chrysene is a readily available material for exploring new polycyclic aromatic hydrocarbons (PAHs). In this study, two chrysene based azahelicenes, nine-membered BA7 and ten-membered DA6, are constructed by intermolecular oxidative annulation of 6-aminochrysene and intramolecular annulation of N ⁶,N ¹²-bis(1-chloronaphthalen-2-yl)chrysene-6,12-diamine, respectively. The hexylated BA7 and DA6 and their brominated products were undoubtedly characterized by single crystal XRD. Subsequent amination with bis(9-methyl-9H-carbazol-3-yl)amine (BMCA) electron donor afforded D-π-D-type semiconductors BA7-BMCA and DA6-BMCA with beneficial properties to act as hole transport materials for perovskite solar cell. Compared with 19.4 % champion power conversion efficiency (PCE) of BA7-BMCA based device, a higher PCE of 20.2 % for DA6-BMCA counterpart may be attributed to its S-shaped double helicene-like linker with extended π-conjugated system.

Doped hole-transporting materials from spiro cores involving 9H-quinolinophenoxazine (spiro-POZ) and 9H-quinolinophenothiazine (spiro-PTZ) show outstanding stability, retaining over 84% of their initial efficiency after more than 300 days of exposure to ambient conditions, and 94% of the power conversion efficiency values after 1200 h under continuous 1 sun illumination.

The improvement of the long-term stability of perovskite-based solar cells (PSCs) toward commercialization is closely linked to the development of cutting-edge charge-transporting materials. The progress on the design and the synthesis of new hole-transporting materials (HTMs) is synergistically attaining both top efficiencies and promising stability. Herein, the synthesis and characterization of two doped-HTMs based on electron-rich spiranic cores, namely, 9H-quinolinophenoxazine (spiro-POZ) and 9H-quinolinophenothiazine (spiro-PTZ), are presented. The novel HTMs exhibit excellent solubility, optimal highest occupied molecular orbital energy, and excellent thermal stability with glass transition temperatures higher than those for spiro-OMeTAD. [(FAPbI₃)_0.87(MAPbBr₃)_0.13]_0.92[CsPbI₃]_0.08-based solar cells using the new spiro-type HTMs deliver power conversion efficiencies (PCEs) around 17% for mesoporous cells, and higher than 18% in planar configurations, matching the PCE of spiro-OMeTAD. Remarkably, doped spiro-POZ and spiro-PTZ exhibit excellent long-term stability in planar devices, retaining over 84% of their initial efficiency after more than 300 days of exposure to ambient conditions. Furthermore, after 1200 h under continuous 1 sun illumination, the PCE of the PSCs based on spiro-POZ and spiro-PTZ decreases by only 6%.

Stability and toxicity of PSCs are bottleneck challenges for their commercial development. Herein, biomimetic Di-g molecules are introduced to the encapsulated FPSCs as the interface layer, which improves the efficiency of 1.01 cm² FPSCs up to 20.29%. Importantly, they demonstrate excellent mechanical stability and lead leakage suppression, the efficiency maintains 85% of initial value without ion leakage under 10 000 bending cycles.

Abstract

Although outstanding power conversion efficiency (PCE) has been achieved in flexible perovskite solar cells, unsatisfactory operational stability and toxicity caused by the moisture transmittance of polymer packaging are still the bottleneck challenges that limit their applications. Herein, inspired by the non-selective permeability of inactivated cell membrane, the diphosphatidyl-glycerol (Di-g) is tactfully introduced as a self-shield interface upon the perovskite layer. 96% of lead leakage is suppressed because the amphipathic Di-g can simultaneously bind tightly to the divalent lead ion and afford an interfacial water-resistance. More importantly, the gradient distribution of lattice residual stress perpendicular to the substrate are optimized. The resultant flexible devices achieve a PCE of 20.29% and 15.01% at effective areas of 1.01 and 21.82 cm² respectively, yielding excellent environmental and mechanical stability. This strategy exhibits the feasibility of developing interfacial encapsulation to stabilize scalable PSCs with negligible lead leakage.

An extended π-conjugated organic spacer, namely TTDMAI, is successfully developed as spacers for 2D Dion–Jacobson perovskites. A champion efficiency of 18.82% is demonstrated due to the improved film quality and preferred crystal vertical orientation thanks to the templated grain growth by the large crystal nuclei size in the precursor solution.

Abstract

2D Dion–Jacobson (DJ) perovskites have become an emerging photovoltaic material with excellent structure and environmental stability due to their lacking van der Waals gaps relative to 2D Ruddlesden–Popper perovskites. Here, a fused-thiophene-based spacer, namely TTDMAI, is successfully developed for 2D DJ perovskite solar cells. It is found that the DJ perovskite using TTDMA spacer with extended π-conjugation length exhibits high film quality, large crystal size and preferred crystal vertical orientation induced by the large crystal nuclei in precursor solution, resulting in lower trap density, reduced exciton binding energy and oriented charge transport. As a result, the optimized 2D DJ perovskite device based on TTDMA (nominal n = 4) delivers a champion PCE up to 18.82%. Importantly, the unencapsulated device based on TTDMA can sustain average 99% of their original efficiency after being stored in N₂ for 4400 h (over 6 months). Moreover, light, thermal, environmental and operational stabilities are also significantly improved in comparison with their 3D counterparts.

Pure formamidinum (FA)-based 2D perovskite solar cells (PSCs) achieve a record power conversion efficiency (PCE) of 21.07% (certified over 20%), the highest efficiency for low-dimensional PSCs (n ≤ 10) reported to date, together with the improved device stability. The high-efficiency device exhibits a narrowed bandgap and unique 2D–3D intermixing phase distribution for improved light absorption and superior charge transport.

Abstract

Owing to their insufficient light absorption and charge transport, 2D Ruddlesden–Popper (RP) perovskites show relatively low efficiency. In this work, methylammonium (MA), formamidinum (FA), and FA/MA mixed 2D perovskite solar cells (PSCs) are fabricated. Incorporating FA cations extends the absorption range and enhances the light absorption. Optical spectroscopy shows that FA cations substantially increase the portion of 3D-like phase to 2D phases, and X-ray diffraction (XRD) studies reveal that FA-based 2D perovskite possesses an oblique crystal orientation. Nevertheless, the ultrafast interphase charge transfer results in an extremely long carrier-diffusion length (≈1.98 µm). Also, chloride additives effectively suppress the yellow δ-phase formation of pure FA-based 2D PSCs. As a result, both FA/MA mixed and pure FA-based 2D PSCs exhibit a greatly enhanced power conversion efficiency (PCE) over 20%. Specifically, the pure FA-based 2D PSCs achieve a record PCE of 21.07% (certified at 20%), which is the highest efficiency for low-dimensional PSCs (n ≤ 10) reported to date. Importantly, the FA-based 2D PSCs retain 97% of their initial efficiency at 85 °C persistent heating after 1500 h. The results unambiguously demonstrate that pure-FA-based 2D PSCs are promising for achieving comparable efficiency to 3D perovskites, along with a better device stability.

The electron transport layer (ETL) plays a crucial part in extracting electrons and optimizing interfacial contact for perovskite solar cells (PVSCs). Herein, the EVA is introduced into PC₆₁BM to promote the orderly molecular stacking of ETLs. The PC₆₁BM:EVA-based MAPbI₃ PVSCs deliver a champion efficiency of 19.32% and regain 80% of initial efficiency after storage under 52% humidity for 1500 h.

Abstract

The electron transport layer (ETL) plays a crucial part in extracting electron carriers while optimizing the interfacial contact of perovskite/electrode in planar heterojunction perovskite solar cells (PVSCs). Despite various ETLs being designed for efficient PVSCs, there exists hardly any research on the effect of molecular stacking order on device performance. Herein, poly(ethylene-co-vinyl acetate) (EVA) is employed as the [6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM) solution additive. The strong binding energy between EVA with PC₆₁BM promotes the molecular stacking order of ETLs, which alleviates the morphology inhomogeneity, possesses a matched energy level, blocks ion migration, and improves the water–oxygen barrier of perovskite devices. The blade-coated MAPbI₃-based PVSCs achieve a power conversion efficiency (PCE) of 19.32% with positive reproducibility and negligible hysteresis, as well as maintain 90% and 80% of the initial PCE after storage under inert and ambient conditions (52% humidity) for 1500 h without encapsulation. This strategy also improves the champion PCE of CsFAMA-based PVSCs to 20.33%. These findings demonstrate that the regulation of molecular stacking order is a valid approach to optimize interfacial charge-carrier recombination in PVSCs, which meet the demand for high-performance ETL in large-area PVSCs and improve the upscaling of the fabrication technology toward practical applications.

A sputtered NiO _x seed layer is employed to promote the adsorption of [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz) self-assembled monolayers. The resulting high-density MeO-2PACz provides an increased passivation, an enhanced hole-selectivity, a favorable energy-level alignment, and a robust physical contact between perovskite and indium tin oxide. The corresponding inverted perovskite solar cell exhibits an impressive efficiency of 19.9%.

Self-assembled monolayers (SAMs) have emerged as effective carrier transport layers in perovskite (PVK) solar cells because of their unique ability to manipulate interfacial property, as well as simple processing and scalable fabrication. However, the defects and pinholes derived from their sensitive adsorption process inevitably deteriorate the final device performance. Herein, a sputtered nickel oxide (NiO _x ) interlayer is used as a seed layer to promote the adsorption of the [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz) SAM on the indium tin oxide (ITO) substrate. The promoted adsorption is attributed to the enhanced tridentate binding between MeO-2PACz and NiO _x relative to the conventional bidentate binding between MeO-2PACz and ITO. In addition, the NiO _x modification can simultaneously improve the passivation ability and hole-selectivity of the MeO-2PACz, provide a favorable energy-level alignment at the ITO/PVK interface, and prevent a direct contact between PVK and ITO. As a consequence, this NiO _x -seeded MeO-2PACz hole transport layer enables a significantly enhanced power conversion efficiency of 19.9% in comparison with 18.4% of the control device. This work provides an effective strategy to improve the performance of the SAM-based photoelectric device.

This study introduces an octyl-diammonium lead iodide (ODAPbI₄) interlayer onto the hole-transporting layer, which significantly reduces nonradiative recombination of wide-bandgap perovskite devices, enhancing the efficiency of wide-bandgap devices beyond 21%. By coupling a semitransparent device with a Cu₂ZnSn(S,Se)₄ (CZTSSe) cell, a four terminal perovskite/CZTSSe tandem cell with a power conversion efficiency of 22.27% is achieved.

Abstract

Wide-bandgap perovskites have attracted substantial attention due to their important role in serving as a top absorber in tandem solar cells (TSCs). However, wide-bandgap perovskite solar cells (PVSCs) typically suffer from severe non-radiative recombination loss and therefore exhibit high open-circuit voltage (V _OC) deficits. To address these issues, a 2D octyl-diammonium lead iodide interlayer is adopted onto the hole-transporting layer to induce the formation of an ultrathin quasi-2D perovskite that is close to the hole-selective interface. This approach not only accelerates hole transfer and retards hole accumulation but also reduces the trap density in the perovskite layer on top, thereby efficiently suppresses non-radiative recombination pathways. Consequently, the champion wide-bandgap device (≈1.66 eV) exhibits a power conversion efficiency (PCE) of 21.05% with a V _OC of 1.23 V, where the V _OC deficit of 0.43 V is among the lowest values for inverted wide-bandgap PVSCs. Moreover, by stacking a semi-transparent perovskite top cell on a 1.1 eV Cu₂ZnSn(S,Se)₄ (CZTSSe) bottom cell, a 22.27% PCE was achieved on a perovskite/CZTSSe four-terminal tandem solar cell, paving the way for all-solution-processed, low-cost, and efficient TSCs with mitigated energy loss in the wide-bandgap top cells.

Nature Communications, Published online: 24 September 2021; doi:10.1038/s41467-021-25644-x

Electro-strictive strain in 3D polycrystalline perovskite is observed, which can lead to an accelerated ion migration under operational conditions. The 1D–3D perovskite, that is, 1D BnPbI₃ perovskite, spatially distributed in the 3D perovskite film and compensating the dangling bonds in the grain boundaries, can effectively inhibit electro-strictive responses and unbalanced charge carrier extraction, realizing ultralong operational stability.

Abstract

3D organic–inorganic hybrid halide perovskite solar cells (pero-SCs) inherently face severe instability issue due to ion migration under operational conditions. This ion migration inevitably results from the decomposition of ionic bonds under lattice strain and is accelerated by the existence of excess charge carriers. In this study, a 1D–3D mixed-dimensional perovskite material is explored by adding an organic salt with a bulk benzimidazole cation (Bn⁺). The Bn⁺ can induce 3D perovskite crystalline growth with the preferred orientation and form a 1D BnPbI₃ perovskite spatially distributed in the 3D perovskite film. For the first time, the electro-strictive response, which has a significant influence on the lattice strain under an electric field, is observed in polycrystalline perovskite. The 1D–3D perovskite can effectively suppress electro-strictive responses and unbalanced charge carrier extraction, providing an intrinsically stable lattice with enhanced ionic bonds and fewer excess charge carriers. As a result, the ion migration behavior of the p-i-n 1D–3D based pero-SC is dramatically suppressed under operational conditions, showing ultra-long-term stability that retains 95.3% of its initial power conversion efficiency (PCE) under operation for 3072 h, and simultaneously achieving an excellent PCE with a hysteresis-free photovoltaic behavior.

A molten-salt-assisted crystallization (MSAC) strategy is developed to improve the grain growth of all-inorganic perovskite films. MSAC enables more active mass transfer and interaction among precursor colloids. Devices based on the MSAC strategy show much increased efficiency to as high as 19.83% with open-circuit voltage as high as 1.2 V.

Abstract

Dynamic manipulation of crystallization is pivotal to the quality of polycrystalline films. A molten-salt-assisted crystallization (MSAC) strategy is presented to improve grain growth of the all-inorganic perovskite films. Compared with the traditional solvent annealing, MSAC enables more intensive mass transfer by means of convection and diffusion, which is beneficial to the interaction among the precursor colloids and to inducing in-plane growth of perovskite grains, resulting in the formation of high-quality perovskite films with suppressed pinhole and crack formation. Additionally, the introduction of molten salt alters the intermediate phases, and thus changes the crystallization pathways by reducing the energy barrier to produce films with desired optical and electrical properties. As a result, the MSAC strategy endows the devices with champion steady-state output efficiency of 19.83% and open-circuit voltage (V _oc) as high as 1.2 V, among the highest for this type of solar cell, thanks to its effectively reduced V _oc deficit.

One-step antisolvent-free hot-coating method is successfully used to fabricate Sn–Pb perovskite solar cells (PSCs) for the first time. Multiple cations are introduced to control the crystallization of the Sn–Pb film which produces PSCs with a champion power conversion efficiency over 15% and robust shelf stability. A novel ecofriendly approach for the fabrication of Sn–Pb PSCs is provided.

Pb-based perovskite solar cells (PSCs) have shown great potential in next-generation photovoltaics. However, the toxicity of Pb remains a big concern. Partial replacement of Pb with Sn is shown to reduce the toxicity of PSCs without considerably compromising the device performance. Currently, Sn–Pb single-junction PSCs have realized a champion power conversion efficiency (PCE) of 21.7%, whereas all perovskite tandem PSCs with a Pb–Sn device as the bottom cell have achieved a PCE of 25.5%. However, the fabrication process of Sn–Pb PSCs is still not ecofriendly due to the use of hazardous organic solvents and antisolvents. Herein, for the first time, a one-step antisolvent-free method is developed to fabricate a high-quality Sn–Pb perovskite film using methylammonium acetate (MAAc) ionic liquid as a green solvent. The crucial effects of multiple organic halides (MOHs) on the crystallization process and characteristics of the Sn–Pb film are comprehensively investigated. After optimizing the film fabrication parameters, PSCs with a champion PCE of 15.42% can be achieved. Moreover, the device exhibits robust stability that shows negligible PCE loss after being stored in N₂ for 720 h. A new avenue to promote the ecofriendly fabrication of efficient Sn–Pb PSCs is opened up.