Chen Weijie

Residual lead iodide, an unavoidable component in perovskite, is a double-edged sword that can exert either good or bad effects on perovskite solar cells. It can contribute to efficiency improvements by passivating defects but is also prone to cause instability due to photodegradation. Proper utilization, such as redistribution, elimination and transformation of residual lead iodide, can maximize its potential.

Abstract

It is widely believed that excess/residual lead iodide (PbI₂) can affect the performance of perovskite solar cells . Moderate PbI₂ can enhance efficiency by passivating defects, while extremely active PbI₂ leads to non-negligible hysteresis effects and reduces device stability. Although several efforts are made to investigate the role of excess PbI₂, its impact is still underestimated. Recent advances further demonstrate the extraordinary potential of modifying excess PbI₂; however, a comprehensive study is required to obtain a deeper understanding. Herein, the important breakthroughs regarding excess PbI₂ are reviewed and the mechanism of excess PbI₂ in terms of efficiency and stability is rethought. In addition, the origins, verification, and regulation of residual PbI₂ are summarized.

The researchers introduce a multifunctional potassium 4-chlorophenyltrifluoroborate salt as additives for perovskite precursor to improve the performance perovskite solar cells by passivating defects, promoting crystallization process of the perovskite film and suppressing non-radiative recombination in the film. The optimal devices show an enhanced efficiency of 24.50% with remarkable thermal and long-term stability.

Abstract

Despite the rapid developments are achieved for perovskite solar cells (PSCs), the existence of various defects in the devices still limits the further enhancement of the power conversion efficiency (PCE) and the long-term stability of devices. Herein, the efficient organic potassium salt (OPS) of para-halogenated phenyl trifluoroborates is presented as the precursor additives to improve the performance of PSCs. Studies have shown that the 4-chlorophenyltrifluoroborate potassium salt (4-ClPTFBK) exhibits the most effective interaction with the perovskite lattice. Strong coordination between BF₃ ⁻/halogen in anion and uncoordinated Pb²⁺/halide vacancies, along with the hydrogen bond between F in BF₃ ⁻ and H in FA⁺ are observed. Thus, due to the synergistic contribution of the potassium and anionic groups, the high-quality perovskite film with large grain size and low defect density is achieved. As a result, the optimal devices show an enhanced efficiency of 24.50%, much higher than that of the control device (22.63%). Furthermore, the unencapsulated devices present remarkable thermal and long-term stability, maintaining 86% of the initial PCE after thermal test at 80 °C for 1000 h and 95% after storage in the air for 2460 h.

Merging orbitals between the defect and perfect crystals within perovskites are found in chemosynthetic foldable hole-transporting materials (HTMs) that convert discrete island trap states to continuous electronic states, and the mini module achieves high efficiency and fill factor.

Abstract

Defective and perfect sites naturally exist within electronic semiconductors, and considerable efforts to reduce defects to improve the performance of electronic devices, especially in hybrid organic–inorganic perovskites (ABX₃), are undertaken. Herein, foldable hole-transporting materials (HTMs) are developed, and they extend the wavefunctions of A-site cations of perovskite, which, as hybridized electronic states, link the trap states (defective site) and valence band edge (perfect site) between the naturally defective and perfect sites of the perovskite surface, finally converting the discrete trap states of the perovskite as the continuous valence band to reduce trap recombination. Tailoring the foldability of the HTMs tunes the wavefunctions between defective and perfect surface sites, allowing the power conversion efficiency of a small cell to reach 23.22% and that of a mini-module (6.5 × 7 cm, active area = 30.24 cm²) to reach as high as 21.71% with a fill factor of 81%, the highest value reported for non-spiro-OMeTAD-based perovskite solar modules.

Publication date: July 2023

Source: Journal of Energy Chemistry, Volume 82

Author(s): Jianjun Sun, Wangchao Chen, Yingke Ren, Yunjuan Niu, Zhiqian Yang, Li'e Mo, Yang Huang, Zhaoqian Li, Hong Zhang, Linhua Hu

Monolithically integrated Cu(In,Ga)Se₂ (CIGS) modules suffer from power losses due to intrinsic shunt current along P1 scribing zone. By KF postdeposition treatment (PDT), the in-plane carrier mobility in CIGS significantly decreases compared to that upon NaF PDT, while the out-of-plane mobility is similar. Such anisotropic mobility is due to carrier scattering by wide-bandgap phases formed at grain boundary area.

The recent efficiency boosting of Cu(In,Ga)Se₂ (CIGS) solar cells is undoubtedly triggered by heavy alkali postdeposition treatments (PDTs). However, the effects are not obvious under monolithically integrated CIGS modules where various current-shunting sources can deteriorate the device performance. Herein, It is reported that KF PDT can effectively suppress the major shunting sources caused by P1 and P3 laser scribing for monolithic interconnection, reducing the cell-to-module (CTM) efficiency gap in CIGS photovoltaics. CIGS with NaF PDT exhibits nearly isotropic and high hole mobilities, causing a large CTM efficiency loss. CIGS with additional KF PDT, on the other hand, reveals much lower in-plane hole mobility than the out-of-plane component, significantly increasing the P1 shunt resistance without exacerbating the photocarrier extraction in the active area. It is suggested that such anisotropic charge transport is due to carrier scattering by low-conductivity phases at the CIGS grain boundaries. Furthermore, passivation of the front junction by KF PDT raises the tolerance to P3 scribing-induced damage, increasing the P3 shunt resistance while preserving the junction property unlike the NaF PDT case. The work implies that the recent trend of employing heavy alkali PDTs for a high-efficiency cell is also crucial for designing a high-efficiency CIGS module.

Perovskite optoelectronics are struggling from chronic instability. Polyvinyl acetate (PVAc)-treated poly(3,4-ethylenedioxythio-4phene:poly(styrene sulfonate) (PEDOT:PSS) is introduced with its highest advantage in the location of PVAc, which is the interface between perovskite and PEDOT:PSS layer and finally could lead to not only ameliorated J–V performance but robust stability under extreme atmosphere (AM 1.5G and 60 °C).

To achieve world's burgeoning appetite in obtaining high-energy conversion efficiency, not only perovskite semiconductor but also hole transporting material (HTM) takes a significant role as a game changer. The dopant of conventional organic HTM induces side effects of degradation, and inorganic HTM reacts or penetrates with the underlying perovskite layer. Considering those issues, poly(3,4-ethylenedioxythiophene:poly(styrene sulfonate) (PEDOT:PSS) as an alternative HTM has been explored in the field of perovskite solar cells with its outstanding hole transporting property. Herein, incorporation of polyvinyl acetate (PVAc) in PEDOT:PSS paves the way to wide applications in device structural perspective, as to say, in n–i–p structure. The presence of the ester group in PVAc donates the bonding site to the perovskite layer, which improves the adhesion, resulting in enhanced charge transport ability as well as device stability. PVAc-treated PEDOT:PSS device exhibited 20% higher power conversion efficiency (PCE) than the PVAc-free device and retained 80% of initial PCE after 1000 h under extreme conditions (AM 1.5G and 60 °C).

This work focuses on using a bi-interfacial HTL strategy and additive engineering to modulate the performance of MA, Br-free formamidine-based perovskite solar cells. Inverted structured devices with NiO _x -based HTLs achieve a high V _OC of 1.14 V and efficiency of 22.78%.

Lead halide-based perovskites solar cells (PSCs) are intriguing candidates for photovoltaic technology due to their high efficiency, low cost, and simple fabrication processes. Currently, PSCs with efficiencies of >25% are mainly based on methylammonium (MA)-free and bromide (Br) free, formamide lead iodide (FAPbI₃)-based perovskites, because MA is thermally unstable due to its volatile nature and Br incorporation will induce blue shift in the absorption spectrum. Therefore, MA-free, Br-free formamidine-based perovskites are drawing huge research attention in recent years. The hole transporting layer (HTL) is crucial in fabricating highly efficient and stable inverted p-i-n structured PSCs by enhancing charge extraction, lowering interfacial recombination, and altering band alignment, etc. Here, this work employs a NiO _x /PTAA bi-layer HTL combined with GuHCl (guanidinium hydrochloride) additive engineering and PEAI (phenylethylammonium iodide) passivation strategy to optimize the charge carrier dynamics and tune defects chemistry in the MA-free, Br-free RbCsFAPbI₃-based perovskite absorber, which boosts the device efficiency up to 22.78%. Additionally, the device retains 95% of its initial performance under continuous 1 sun equivalent LED light illumination at 45 °C for up to 500 h.

Polyvinyl pyrrolidone (PVP) is doped to PbI₂ and organic salt, so as to regulate the crystallization process of halide perovskite. PVP doping can reduce crystallite size to a certain extent, due to the confinement effect provided by the long polymer chains of PVP. Interestingly, such an effect is helpful for both efficiency and stability (especially the thermal stability) of perovskite solar cells.

Abstract

Polyvinyl pyrrolidone (PVP) is doped to PbI₂ and organic salt during two-step growth of halideperovskite. It is observed that PVP molecules can interact with both PbI₂ and organic salt, reduce the aggregation and crystallization of the two, and then slow down the coarsening rate of perovskite. As doping concentration increases from 0 to 1 mM in organic salt, average crystallite size of perovskite decreases monotonously from 90 to 34 nm; Surface fluctuation reduces from 259.9 to 179.8 nm at first, and then increases; Similarly, surface roughness decreases from 45.55 to 26.64 nm at first, and then rises. Accordingly, a kind of “confinement effect” is resolved to crystallite growth and surface fluctuation/roughness, which helps to build compact and uniform perovskite film. Density of trap states (t-DOS) is cut down by ≈60% at moderate doping  (0.2 mM). Due to the “confinement effect”, power conversion efficiency of perovskite solar cells is improved from 19.46 (±2.80) % to 21.50 (±0.99) %, and further improved to 24.11% after surface modification. Meanwhile, “confinement effect” strengthens crystallite/grain boundaries and improves thermal stability of both film and device. T ₈₀ of device increases to 120 h, compared to 50 h for reference ones.

A facile strategy was developed to improve the film quality of a solution processed nickel(II) nitrate hole transporting layer, which realized a record efficiency of 19.02 % for the binary blend bulk heterojunction organic solar cells.

Abstract

A facile strategy was developed here to improve the film quality of nickel-based hole transporting layer (HTL) for efficient organic solar cell (OSC) applications. To prevent the agglomeration of Ni(NO₃)₂ during film deposition, acetylacetonate was added into the precursor solution, which led to the formation of an amorphous and glass-like state. After thermal annealing (TA) treatment, the film-forming ability could be further improved. The additional UV-ozone (UVO) treatment continuously improved the film quality and increased the work function and conductivity of such HTL. The resulting TA & UVO modified Ni(NO₃)₂ & Hacac HTL produced highly efficient organic solar cells with exciting power conversion efficiencies of 18.42 % and 19.02 % for PM6 : BTP-eC9 and D18 : BTP-Th devices, respectively, much higher than the control PEDOT : PSS devices.

The bionic high-speed patterned (BHSP) meniscus coating process is introduced to induce the polymer chain-oriented deposition in the stretchable perovskite solar cells (PSCs), generating in the practical application of the stretchable PSCs and avoid the stress damage to the device. The stretchable PSCs achieve a stabilized power conversion efficiency of 20.04% (1.01 cm²) and 16.47% (9 cm²) with minor efficiency discrepancy.

Abstract

Polymer matrix is felicitously applied into the active layer and transporting layer of perovskite solar cells (PSCs) to enable a stretchable function. However, the chaotic deposition of polymer chains is the main cause for the inferior photoelectric performance. When the stretchable PSCs are in a working state, the stress cannot be removed effectively due to the random polymer chain deposition. The stress accumulation will cause irreversible damage to the stretchable PSCs. Herein, the structural bionics and patterned-meniscus coating technology are combined to print the polymer chain-oriented deposition in the stretchable PSCs. Based on this approach, the conducting polymer electrode is printed with both significant mechanical stability and conductivity. More importantly, the oriented polyurethane with self-healing property can enhance the crystal quality of perovskite films and repair perovskite cracks caused by stress destruction. Thus, the corresponding stretchable PSCs achieve a stabilized power conversion efficiency (PCE) of 20.04% (1.0 cm²) and 16.47% (9 cm²) with minor efficiency discrepancy. Notably, the stretchable PSCs can maintain 86% of the primitive PCE after 1000 cycles of bending with a stretch ratio of 30%. This directional growth of polymer chain strategy provides guidance for printing prominent-performance stretchable PSCs.

A family of isomeric small molecule donors based on benzodithiophene–terthiophene core with linear, the 1st carbon and 2nd carbon position branched butyl-based rhodanine are synthesized. SM-s-Bu:BO-4Cl-based ASM-OSCs show an impressive power conversion efficiency with over 16% and excellent storage stability with a T ₈₀ of over 1700 h, which is one of the top-level results among BTR-series small molecule donors in binary all-small-molecule organic solar cells.

Abstract

All-small-molecule organic solar cells (ASM-OSCs) are challenging for their inadequate efficiency and device stability due to their more susceptive morphology. Herein, a family of isomeric small molecule donors (SMDs) is synthesized based on the benzodithiophene–terthiophene core with linear, 1st carbon, and 2nd carbon position branched butyl-based rhodanine for ASM-OSCs, respectively. The single crystal of thiophene-substituted model T-s-Bu forms a more compact intermolecular packing with herringbone structure than slip-layered packing-based T-n-Bu and T-i-Bu. SM-i-Bu and SM-s-Bu show slightly blue-shifted absorption and deepened HOMO levels in the neat film compared to SM-n-Bu. SM-s-Bu:BO-4Cl blend films have distinct face-on packing orientations and suitable fibrous phase separation along with more apparent microcrystals. Finally, SM-s-Bu:BO-4Cl-based device yields an improved power conversion efficiency of 16.06% compared to 15.12% and 8.22% for SM-n-Bu:BO-4Cl and SM-i-Bu:BO-4Cl, which is one of the top-ranked results for BTR-series SMDs in binary ASM-OSCs. More importantly, the excellent storage stability with a T ₈₀ lifetime of over 1700 h and decent thermal stability is realized in SM-s-Bu:BO-4Cl. This work highlights that the isomeric terminal alkyl with a branching point directly connected to the backbone for SMDs is a promising strategy for improving the crystal packing and film morphology and achieving highly efficient and stable ASM-OSCs.

A nitroxide radical side chain substituted conjugated polymer, GDTA, employed as a solid additive to generally boost the power conversion efficiencies of organic solar cells from a broad range of photovoltaic material systems, especially for the nonfullerene acceptor-based cells, is reported.

Abstract

Nonfullerene-acceptor-based organic solar cells (NFA-OSCs) are now set off to the 20% power conversion efficiency milestone. To achieve this, minimizing all loss channels, including nonradiative photovoltage losses, seems a necessity. Nonradiative recombination, to a great extent, is known to be an inherent material property due to vibrationally induced decay of charge-transfer (CT) states or their back electron transfer to the triplet excitons. Herein, it is shown that the use of a new conjugated nitroxide radical polymer with 2,2,6,6-tetramethyl piperidine-1-oxyl side groups (GDTA) as an additive results in an improvement of the photovoltaic performance of NFA-OSCs based on different active layer materials. Upon the addition of GDTA, the open-circuit voltage (V _OC), fill factor (FF), and short-circuit current density (J _SC) improve simultaneously. This approach is applied to several material systems including state-of-the-art donor/acceptor pairs showing improvement from 15.8% to 17.6% (in the case of PM6:Y6) and from 17.5% to 18.3% (for PM6:BTP-eC9). Then, the possible reasons behind the observed improvements are discussed. The results point toward the suppression of the CT state to triplet excitons loss channel. This work presents a facile, promising, and generic approach to further improve the performance of NFA-OSCs.

Polymer solar cells (PSCs) with high-performance and -stretchability are developed by designing block copolymer donors comprising PM6 and elastomeric PDMS blocks (PM6-b-PDMS). High power conversion efficiency (PCE ≈ 18%) and stretchability (crack onset point > 18%) are demonstrated for the PM6-b-PDMS_19k-based PSC. The PM6-b-PDMS_19k-based intrinsically stretchable PSCs show superior mechanical stability (PCE retention > 80% at 32% strain) than the PM6-based and PM6:PDMS-blend-based devices.

Abstract

High power conversion efficiency (PCE) and stretchability are the dual requirements for the wearable application of polymer solar cells (PSCs). However, most efficient photoactive films are mechanically brittle. In this work, highly efficient (PCE = 18%) and mechanically robust (crack-onset strain (COS) = 18%) PSCs are acheived by designing block copolymer (BCP) donors, PM6-b-PDMSx (x = 5k, 12k, and 19k). In these BCP donors, stretchable poly(dimethylsiloxane) (PDMS) blocks are covalently linked with the PM6 blocks to effectively increase the stretchability. The stretchability of the BCP donors increases with a longer PDMS block, and PM6-b-PDMS_19k:L8-BO PSC exhibits a high PCE (18%) and 9-times higher COS value (18%) compared to that (COS = 2%) of the PM6:L8-BO-based PSC. However, the PM6:L8-BO:PDMS_12k ternary blend shows inferior PCE (5%) and COS (1%) due to the macrophase separation between PDMS and active components. In the intrinsically stretchable PSC, the PM6-b-PDMS_19k:L8-BO blend exhibits significantly greater mechanical stability PCE_80% ((80% of the initial PCE) at 36% strain) than those of the PM6:L8-BO blend (PCE_80% at 12% strain) and the PM6:L8-BO:PDMS ternary blend (PCE_80% at 4% strain). This study suggests an effective design strategy of BCP P _D to achieve stretchable and efficient PSCs.

The molecule-aggregate-domain transition dynamic process assisted by the volatile solid additive 2-hydroxy-4-methoxybenzophenone (2-HM) is demonstrated, the role of 2-HM in individual donor and acceptor systems is unlocked, and its function in altering the bulk heterojunction to achieve forefront ≈19% efficiency for binary organic nonfullerene solar cells is further revealed.

Abstract

Organic nonfullerene solar cells (ONSCs) have made unprecedented progress; however, morphology optimization of ONSCs is proven to be particularly challenging relative to classical fullerene-based devices. Here, a novel volatile solid additive (VSA), 2-hydroxy-4-methoxybenzophenone (2-HM), is reported for achieving high-efficiency ONSCs. 2-HM functions as a universal morphology-directing agent for several well-known PM6:Y6 series nonfullerene blends, viz. PM6:Y6, PM6:BTP-eC9, PM6:L8-BO, leading to a best efficiency of 18.85% at the forefront of reported binary ONSCs. VSAs have recently emerged, while the intrinsic kinetics is still unclear. Herein, a set of in situ and ex situ characterizations is employed to first illustrate the molecule-aggregate-domain transition dynamic process assisted by the VSA. More specifically, the role of 2-HM in individual donor PM6 and acceptor Y6 systems is unlocked, and the function of 2-HM in altering the PM6:Y6 bulk heterojunction blends is further revealed for enhanced photovoltaic performance. It is believed that the achievement brings not only a deep insight into emerging volatile solid additive, but also a new hope to further improve the molecular ordering, film microstructure, and relevant performance of ONSCs.

Publication date: 15 March 2023

Source: Joule, Volume 7, Issue 3

Author(s): Yi Yang, Jingwen Wang, Yunfei Zu, Qing Liao, Shaoqing Zhang, Zhong Zheng, Bowei Xu, Jianhui Hou

Nature Energy, Published online: 16 March 2023; doi:10.1038/s41560-023-01227-6

Nature Energy, Published online: 16 March 2023; doi:10.1038/s41560-023-01220-z

Herein, a simple method for growing 2D perovskites via a solid-phase reaction at the perovskite/carbon interface when fabricating carbon electrode using a hot-pressing process is presented. The in situ formed 2D perovskite interlayer not only passivates surface defects but also enables a seamless contact at perovskite/carbon interface and promotes carrier transport.

Carbon-based perovskite solar cells (C-PSCs) without hole transport layer have piqued the interest of researchers due to their low-cost fabrication processes and exceptional stability. However, the efficiency of C-PSCs lags far behind that of state-of-the-art metal-based devices, owing to an energy-level mismatch and poor interfacial contact at the interface between carbon electrode and perovskite layer. Herein, a simple method for performing a solid-phase reaction at the perovskite/carbon interface using a hot-pressing process is presented. Unlike the solution processes commonly used in PSCs to obtain 2D halide perovskite layers, butylammonium iodide (BAI) is introduced into carbon electrodes, which are then hot pressed onto 3D perovskite in this work. During hot pressing, BAI in the carbon electrode reacts with the 3D perovskite layer to form a 2D perovskite layer at the perovskite/carbon interface through a solid-phase reaction, resulting in a contiguous contact perovskite/carbon interface and better energy-level alignment. Charge recombination at the perovskite/carbon interface is greatly reduced thanks to the seamless contact and the in situ formed 2D perovskite layer as passivation and electron blocking layer. This strategy results in a high power conversion efficiency of up to 16.86% and significantly improved the device stability for C-PSCs.

Herein, a sequential surface modification strategy for high-fill-factor (over 85%) inverted perovskite solar cells through treatment on both wet and dry metal–halide perovskite film is reported using acetic acid and using 4-(dimethylamino) benzoic acid, respectively.

Even the most efficient inverted p–i–n architecture perovskite solar cells (PSCs) are still inferior to those with regular n–i–p architecture, which is mainly limited by interfacial loss. Herein, both wet and dry metal–halide perovskite films are regulated through organic molecules–assisted sequential interfacial engineering for high-performance inverted PSCs. In specific, organic acetic acid treatment on the wet film potently regulates the nucleation and crystallization of perovskite films. Then, further loading 4-(dimethylamino)benzoic acid on the dry perovskite film creates a passivating agent layer to suppress defect formation, leading to more phase-pure and conductive perovskite films. Combined experimental and theoretical results illustrate that such sequential treatment is beneficial for decreasing surface trap states, non-radiative recombination, and carrier transport loss. As a result, the target inverted PSC exhibits an unprecedented high fill factor (FF) of 85.31% together with a champion efficiency of 21.37%, which is greatly improved relative to the reference (FF of 79.60%, and efficiency of 19.40%). It should be noted that such a high FF is among the highest report and corresponding to 94.38% of the Shockley–Queisser limited FF (90.39%) of PSCs with a bandgap of 1.576 eV. In addition, the storage stability against moisture of target inverted PSCs is remarkably enhanced.

The introduction of 3-AzTca regulates the mineralization of PbI₂ and perovskite by strengthening the metallic Pb frame, thereby reducing the defects and improving the environmental stability of PbI₂ and perovskite film. The champion perovskite solar cell achieves a low voltage deficit of 0.37 V, an efficiency of 22.79%, and enhanced stability.

Abstract

Both the uncoordinated Pb²⁺ and excess PbI₂ in perovskite film will create defects and perturb carrier collection, thus leading to the open-circuit voltage (V _OC) loss and inducing rapid performance degradation of perovskite solar cells (PSCs). Herein, an additive of 3-aminothiophene-2-carboxamide (3-AzTca) that contains amide and amino and features a large molecular size is introduced to improve the quality of perovskite film. The interplay of size effect and adequate bonding strength between 3-AzTca and uncoordinated Pb²⁺ regulates the mineralization of PbI₂ and generates low-dimensional PbI₂ phase, thereby boosting the crystallization of perovskite. The decreased defect states result in suppressed nonradiative recombination and reduced V _OC loss. The power conversion efficiency (PCE) of modified PSC is improved to 22.79% with a high V _OC of 1.22 V. Moreover, the decomposition of PbI₂ and perovskite films is also retarded, yielding enhanced device stability. This study provides an effective method to minimize the concentration of uncoordinated Pb²⁺ and improve the PCE and stability of PSCs.

In this study, polysuccinimide is used as the additive in printable mesoscopic perovskite solar cells. It improves the perovskite crystallinity and its carbonyl groups strongly coordinate with Pb²⁺, which can effectively passivate defects. As a result, the device has an average V _OC increases over 40 mV and the champion device has a PCE of 18.84%

Abstract

Due to the low cost and excellent potential for mass production, printable mesoscopic perovskite solar cells (p-MPSCs) have drawn a lot of attention among other device structures. However, the low open-circuit voltage (V _OC) of such devices restricts their power conversion efficiency (PCE). This limitation is brought by the high defect density at perovskite grain boundaries in the mesoporous scaffold, which results in severe nonradiative recombination and is detrimental to the V _OC. To improve the perovskite crystallization process, passivate the perovskite defects, and enhance the PCE, additive engineering is an effective way. Herein, a polymeric Lewis base polysuccinimide (PSI) is added to the perovskite precursor solution as an additive. It improves the perovskite crystallinity and its carbonyl groups strongly coordinate with Pb²⁺, which can effectively passivate defects. Additionally, compared with its monomer, succinimide (SI), PSI serves as a better defect passivator because the long-chained macromolecule can be firmly anchored on those defect sites and form a stronger interaction with perovskite grains. As a result, the champion device has a PCE of 18.84%, and the V _OC rises from 973 to 1030 mV. This study offers a new strategy for fabricating efficient p-MPSCs.

The methylenediaminium dichloride (MDACl₂) is used to control the crystallization of wide-bandgap pure-iodine FA_0.5Cs_0.5PbI₃ perovskite films. The MDACl₂ can control the whole crystallization process of perovskite films, including both nucleation and crystal growth. The dual effects of MDACl₂ contribute to the improved crystallization quality of the perovskite films, resulting in a high efficiency of 18.52% for carbon-based perovskite solar cells.

Abstract

Wide-bandgap perovskite is a vital part of perovskite-based tandem solar cells. Currently, wide-bandgap perovskites are typically based on mixed-halide (I/Br) materials, but suffer from photoinduced phase separation. The pure-iodide formamidine/cesium (FA/Cs) based FA _x Cs_{1− x} PbI₃ perovskites with high Cs content are good candidates, whereas the control of crystallization is challenging due to the complex crystallization kinetics. Here, pure-iodide FA_0.5Cs_0.5PbI₃ wide-bandgap perovskite solar cells is reported. As an acidic diammonium salt, methylenediaminium dichloride (MDACl₂) is applied as an additive to control the whole crystallization process of perovskite films, including both nucleation and crystal growth. Starting from the solution chemistry, the MDACl₂ additive with acidity and strong solvation properties can effectively regulate the chemical composition of perovskite precursor, thus inhibiting the growth of undesired 1D intermediates during the nucleation process. Besides, the incorporation of larger-sized MDA²⁺ into the lattice compensates for the tolerance factor and accelerates the ion exchange reaction between FA⁺ and Cs⁺ in the crystal growth process. As a result, the crystallinity of the perovskite films is significantly improved, benefitting from the dual function of MDACl₂. Finally, the efficiency of hole transport layer-free carbon electrode-based wide-bandgap perovskite solar cells reaches 18.52%, which is the highest reported so far.

New small molecule donors with 2D symmetric/asymmetric hybrid cyclopentyl-hexyl side chains are developed for high performance all-small-molecular organic solar cell (ASM-OSCs). This synergistic strategy endows the blends with controlled intermolecular interaction, donor/acceptor interfacial energetics, and suitable nanoscale bicontinuous phase separation, and enables the device to exhibit a power conversion efficiency of 16.46%.

Abstract

All small molecule organic solar cells (ASM-OSCs) have numerous advantages but lower power conversion efficiencies (PCEs) than their polymer equivalents, which is largely due to the suboptimal nanoscale network structure in a bulk heterojunction (BHJ). Herein, new small molecule donors with symmetric/asymmetric hybrid cyclopentyl-hexyl side chains are designed, accounting for manipulated intermolecular interactions and BHJ morphology. Theoretical and experimental results reveal that the asymmetric cyclopentyl-hexyl side chains modification has a significant influence on potential energy surface and intermolecular interaction that can ensure preferable molecular assembly and regulate the D/A interfacial energetics, thus boosting the exciton dissociation and charge transport when pairing with a wide-used acceptor L8-BO. Concurrently, a nanoscale bicontinuous interpenetrating network with optimal domain size can be fully evolved in the BHJ layer. As a consequence, the As-TCp-based binary device achieves a superior PCE of 16.46% in comparison to that of the controlled symmetric counterparts S-BF (14.92%) and A-TCp (15.77%), and ranks one of best performance among ASM-OSCs. This study demonstrates that precise manipulation of the cyclo-alkyl chain in combination with the asymmetric 2D side chain strategy is an effective synergistic approach to control intermolecular interaction and nanoscale bicontinuous phase separation for achieving high-performance ASM-OSCs.

In this work, an innovative in situ etching treatment method to reduce surface defects of CsPbI_2.85Br_0.15 perovskite films by using methanol without additional passivator is proposed. A slight excess of PbI₂ is generated on perovskite surface, which is beneficial to form gradient energy level alignment. Eventually, a champion CsPbI_2.85Br_0.15 inorganic perovskite solar cell with efficiency of 19.34% is achieved.

Abstract

Inorganic perovskite solar cells (IPSCs) have developed rapidly due to their good thermal stability and the bandgap suitable for perovskite/silicon tandem solar cells. However, the large open-circuit voltage (V_OC) deficit derived from the surface defects and the energy level structure mismatch impede the development of device performance, especially in the P-I-N structure IPSCs. Herein, an innovative in situ etching (ISE) treatment method is proposed to reduce surface defects through methanol without additional passivator. It is found that the perovskite films treated with methanol result in a slight excess of PbI₂ on the surface and inserted into the grain boundaries. Therefore, the successful decrease of surface defects by methanol and the passivation of grain boundary defects by PbI₂ greatly reduce the trap density of perovskite films. And the larger work function of PbI₂ contributes to the energy band of perovskite surface bending downward and forms gradient energy level alignment at the I/N interface, which accelerates extraction of charge carriers. As a result, the efficiency of CsPbI_2.85Br_0.15 inverted IPSC is enhanced from 16.00% to 19.34%, which is one of the mostly efficient IPSCs. This work provides an original idea without additional passivator to manage the defects of inorganic perovskite.