Chen Weijie

Publication date: October 2022

Source: Nano Energy, Volume 101

Author(s): Qiuju Jiang, Pengwei Han, Haijun Ning, Jiaquan Jiang, Hui Chen, Yonghong Xiao, Chun-Rong Ye, Jinming Chen, Man Lin, Feng He, Xiao-Chun Huang, Qinghe Wu

Thermalization loss limits the efficiency of OSCs. By integrating with wide bandgap CsPbI₂Br, a tandem solar cell is demonstrated with a remarkable voltage of 2.116 V with ≈0.001 V voltage loss through a TA-free process in depositing of organic rear cell. This work demonstrates the great potential of tandem solar cell incorporating perovskite and organic absorber.

Abstract

Organic solar cells (OSCs) based on polymer donor and non-fullerene acceptor achieve power conversion efficiency (PCE) more than 19% but their poor absorption below 550 nm restricts the harvesting of high-energy photons. In contrast, wide bandgap all-inorganic perovskites limit the absorption of low-energy photons and cause serious below bandgap loss. Therefore, a 2-terminal (2T) monolithic perovskite/organic tandem solar cell (TSC) incorporating wide bandgap CsPbI₂Br is demonstrated as front cell absorber and organic PM6:Y6 blend as rear cell absorber, to extend the absorption of OSCs into high-energy photon region. The perovskite sub-cell, featuring a sol–gel prepared ZnO/SnO₂ bilayer electron transporting layer, renders a high open-circuit voltage (V _OC). The V _OC is further enhanced by employing thermal annealing (TA)-free process in the fabrication of rear sub-cell, demonstrating a record high V _OC of 2.116 V. The TA-free Ag/PFN-Br interface in organic sub-cell facilitates charge transport and restrains nonradiative recombination. Consequently, a remarkable PCE of 20.6% is achieved in monolithic 2T-TSCs configuration, which is higher than that of both reported single junction and tandem OSCs, demonstrating that tandem with wide bandgap all-inorganic perovskite is a promising strategy to improve the efficiency of OSCs.

The intercalation of perovskite quantum dots between perovskites and NiO _x hole transport layers is introduced to promote steric arrangements and electronic properties of NiO _x nanoparticles. The performances of NiO _x -based n-i-p perovskite solar devices are significantly improved, realizing high efficiency (21.59%) and excellent stability (sustaining 85 °C/85% RH aging test).

Abstract

Power conversion efficiency (PCE) and long-term stability are two vital issues for perovskite solar cells (PSCs). However, there is still a lack of suitable hole transport layers (HTLs) to endow PSCs with both high efficiency and stability. Here, NiO _x nanoparticles are promoted as an efficient and 85 °C/85%-stable inorganic HTL for high-performance n-i-p PSCs, with the introduction of perovskite quantum dots (QDs) between perovskite and NiO _x as systematic interfacial engineering. The QD intercalation enhances film morphology and assembly regulation of NiO _x HTLs . Due to structure–function correlations, hole mobility within NiO _x HTL is improved. And the hole extraction from perovskite to NiO _x is also facilitated, resulting from reduced trap states and optimized energy level alignments. Hence, the promoted NiO _x -based n-i-p PSCs exhibit high PCE (21.59%) and excellent stability (sustaining 85 °C aging in air without encapsulation). Furthermore, encapsulated solar modules with QDs-promoted NiO _x HTLs show impressive stability during 85 °C/85% aging test for 1000 hours. With high transparency, QDs-promoted NiO _x is also demonstrated to be an advanced HTL for semitransparent PSCs. This work develops promising NiO _x inorganic HTL in n-i-p PSCs for manufacturing next-generation photovoltaic devices.

Using 4-fluoro-phenylethylammonium iodide as a dual-functional agent, a synergetic strategy is proposed to effectively enhance the crystallinity, passivate the defects, and suppress nonradiative recombination of a wide-bandgap perovskite. Excellent power conversion efficiency up to 19.1% is achieved for the modified perovskite solar cells with improved moisture stability.

Abstract

Wide-bandgap (WBG) perovskite solar cells (PSCs) suffer from severe voltage loss, which significantly limits the enhancement of photovoltaic performance. Here, 4-fluoro-phenylethylammonium iodide (FPEAI) is used as a dual-functional agent for oriented crystallization and comprehensive passivation of WBG PSCs. The additive of FPEAI promotes crystals to grow along with the (100) orientation with improved crystallinity and to spontaneously form Ruddlesden–Popper 2D perovskite on the grain boundary and surface of 3D crystals, which can passivate defects and protect the perovskite film from moisture erosion as well as suppressed ion migration. In addition, the 2D/3D heterostructure induces a matched energy-level alignment, which mitigates the detrimental interfacial charge recombination at the interface of the 3D perovskite and hole transport layer. Consequently, the modified WBG PSCs exhibit an improved open-circuit voltage to 1.3 V and a fill factor of 77.8%, leading to a remarkable power conversion efficiency of 19.1% with negligible hysteresis. Furthermore, the WBG PSCs maintain 85% of the original efficiency after 1000 h in air, demonstrating outstanding humidity stability. This work indicates that FPEAI can be used as a dual-functional agent to significantly enhance the efficiency of WBG PSCs.

2D conjugated covalent organic frameworks, TTDA-TAPB-COF and TTDA-TTA-COF, are designed to simultaneously suppress charge recombination and decomposition of perovskite materials. The champion perovskite solar cell with TTDA-TTA-COF exhibits a power conversion efficiency of 23.35% and excellent long-term stability. To the best of one's knowledge, this is the highest efficiency in perovskite solar cells using the strategy of crystalline organic frameworks.

Abstract

The power conversion efficiency (PCE) of perovskite solar cells (PSCs) has rapidly increased over the past 10 years. However, along with further efficiency improvements, it is necessary to improve the long-term stability of perovskite materials, which limits the commercialization of PSCs. Therefore, it is urgent to find ways to simultaneously suppress charge recombination and degradation of perovskite materials. Here, two covalent organic frameworks (COFs) are synthesized by reacting thieno[3,2-b]thiophene-2,5-dicarbaldehyde (TTDA) with 1,3,5-tris(4-aminophenyl)benzene (TAPB) or 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TTA). The addition of these two COFs to the perovskite layer allows for more efficient charge separation through spatially separated frontier orbitals, and can also inhibit the degradation of the FAPbI₃ layer and the formation of δ-FAPbI₃. The PSCs with TTDA-TTA-COF exhibit higher efficiency and open-circuit voltage than those with TTDA-TAPB-COF. This is attributed to the better crystallization of perovskites induced by stronger well-conjugated properties and π–π interactions in TTDA-TTA-COF. The champion PSC with TTDA-TTA-COF exhibits a PCE of 23.35% and excellent long-term stability. To the best of one's knowledge, this is the highest efficiency among PSCs fabricated using crystalline organic frameworks as additives. This work provides a new route to fabricate efficient and stable PSCs by incorporating proper COFs.

A sticker-type ultra-thin perfluoropolyether anti-reflective film (SUPA) is fabricated through a two-step peeling propagation method. The SUPA-assisted rigid and flexible perovskite solar cell guarantees high short-circuit current density (rigid ≈26.63 mA cm⁻², flexible ≈23.05 mA cm⁻²) and power conversion efficiency (rigid ≈24.31%, flexible ≈20.05%) with mechanical and long-term stability.

Abstract

Sticker-type anti-reflective (AR) film is a powerful route to achieve the highest efficiency and commercialization of perovskite solar cells (PSCs) by improving the light transition efficiency (LTE). However, conventionally used AR film has high flexural rigidity owing to its limitation of material and thickness, thereby hindering its application to high-efficiency flexible devices. This paper proposes a sticker-type ultra-thin perfluoropolyether (PFPE) AR film (SUPA) made of PFPE (n = 1.34) that is fabricated through a well-designed two-step peeling propagation method. The proposed SUPA demonstrates superior properties in terms of LTE (≈98.3%) and film thickness (≈20 µm), exhibiting the best performance among the existing AR films for PSCs. The SUPA-assisted rigid and flexible PSC guarantees high short-circuit current density (rigid ≈26.63 mA cm⁻², flexible ≈23.05 mA cm⁻²) and power conversion efficiency (rigid ≈24.31%, flexible ≈20.05%). The SUPA sustains over 97.5% of its initial transmittance under exposure to the light (168 h) and damp heat condition (1000 h), and devices with SUPA show remarkable flexibility maintaining their initial efficiency after 10 000 cycles of a bending test (2 mm radius).

The authors design and synthesize a new benzo[1,2-b:4,5-b′]difuran (BDF)-based polymer donor named D18-Fu. The D18-Fu-based devices can achieve an excellent efficiency of 17.07% with a high fill factor (FF) of 80.4%, both of which are the highest values among those of BDF polymer-based devices.

Abstract

In the field of non-fullerene organic solar cells (OSCs), most of the promising polymer donors are based on benzo[1,2-b:4,5-b′]dithiophene (BDT) units while benzo[1,2-b:4,5-b′]difuran (BDF)-based polymers have drawn less attention since the efficiencies of BDF polymer-based devices are generally lower than those of BDT polymer-based ones. In this contribution, the BDT unit in a polymer donor named D18 is replaced with a BDF unit, and a new polymer named D18-Fu is synthesized. As a highly-crystalline molecule named Y6-1O is chosen as the acceptor, the efficiency of binary devices based on D18-Fu can reach 16.38%. Furthermore, when one of fullerene derivatives PC₇₁BM is added, the ternary devices based on D18-Fu achieve an efficiency of 17.07% and a high fill factor (FF) of 80.4%, both of which are the highest values among those of BDF polymer-based devices. For comparison, D18-based ternary devices show an inferior efficiency of 15.61% mainly due to the lower FF of 73.9%. Subsequent characterization reveals that D18-Fu possesses a more coplanar molecular geometry, leading to better morphology and higher charge mobility for a promising FF. The high performance shown in this work demonstrates the potential role of BDF units in the design of polymer donors for highly efficient OSCs.

Organic solar cells (OSCs) are a promising next-generation photovoltaic technology with many unique advantages. This Minireview highlights the recent advances in material design and cutting-edge devices. Particular attention is paid to a few research directions toward practical applications of OSCs.

Abstract

Single-junction organic solar cells (OSCs) have made significant progress in recent years. Innovations in material design and device optimization have improved the power conversion efficiencies to over 19 %. In this Minireview, based on recent advances, we discuss molecular design strategies to tune the absorption spectrum, energy level, and intermolecular aggregation as well as highlight the role of molecular electrostatic potential in decreasing energy loss. Then, we introduce the latest progress in four types of OSCs composed of different donor:acceptor combinations: polymer donor:small-molecule acceptor, all-polymer, all-small-molecule, and small-molecule donor:polymer acceptor. Finally, the challenges of OSCs in practical applications, including material cost, stability, and multi-function integration, are discussed.

Through the film post-treatment process, N-hydroxysuccinimide is introduced into the perovskite/spiro-OMeTAD interface without damaging the perovskite films. N-hydroxysuccinimide molecules are located at perovskite grain boundary and surface with good compability with the perovskite crystal network, which forms an effective barrier at the grain boundary to prevent the permeation of moisture. The efficiency and stability of the device are significantly enhanced.

Nonradiative recombination on perovskite surface and grain boundary largely constrains the efficiency and stability of photovoltaic devices. Surface passivation has proven to be the most effective strategy to suppress photogenerated carrier recombination. Herein, functional N-hydroxysuccinimide (NHS) is incorporated in perovskite films by suppressing nonradiative losses both in surface and in grain boundary. The NHS molecules are located at the perovskite grain boundary and surface with good compability with the perovskite crystal network, which forms an effective barrier at the grain boundary to prevent the permeation of moisture. Equally important, the interactions between the CO group in NHS and perovskite undercoordinated groups (Pb²⁺ or Pb clusters) reduce the surface defects of the perovskite, yielding a minimal energy loss. The prolonged lifetime of carriers with NHS-treated perovskites prevents the carrier quenching at the perovskite grain boundary and interface. As a result, open-circuit voltage of the solar cell is up to 1.13 V with a power conversion efficiency (PCE) of 22.21%. The stability of the device is also significantly improved, wherein devices with NHS retain 81% of the initial PCE after 1000 h at room temperature.

Publication date: October 2022

Source: Nano Energy, Volume 101

Author(s): Cheng Wang, Maning Liu, Sunardi Rahman, Hannu Pekka Pasanen, Jingshu Tian, Jianhui Li, Zhifeng Deng, Haichang Zhang, Paola Vivo

Transparent conductive oxide- and dopant-free asymmetric structured crystalline silicon heterojunction solar cells are designed to minimize the optical parasitic absorption losses by using rubidium fluoride/aluminum electron-selective contact and molybdenum oxide/silver hole-selective contact. Combined with the use of a thin titanium oxide interlayer to passivate the electron-selective contact interface, an efficiency of 22.9% is realized.

Abstract

Minimizing the optical parasitic absorption loss in hydrogenated amorphous silicon (a-Si:H) and transparent conductive oxide (TCO) layers is considered an effective approach to further improve the power conversion efficiencies (PCEs) of crystalline silicon heterojunction (SHJ) solar cells. In this work, carrier-selective passivating contacts for both polarities, e.g., alkali fluoride/aluminum electron-selective contact and transition metal oxide/silver hole-selective contact, are used to completely replace the doped a-Si:H layers in SHJ solar cell, forming a totally TCO- and dopant-free asymmetric structure. By minimizing the charge carrier transporting and recombination losses on the front-side electron-selective contact through interface engineering, an improved photovoltaic performance with a short-circuit current density of 40.5 mA cm⁻², an open-circuit voltage of 0.709 V, and a fill factor of 79.6% is realized, resulting in a final PCE exceeding 22.9%. The successful demonstration of this work provides an effective way to further boost the efficiency, as well as reduce the cost of SHJ solar cells with a TCO-free and doped a-Si:H-free configuration, using a moderate and simplified fabrication process.

The efficient Ag/MgF₂/Ag micro-cavity electrode is constructed to demonstrate vivid colors of blue, green, and red by adjusting the thickness of the MgF₂ dielectric layer. Meanwhile, the colorful semitransparent organic solar cells based on micro-cavity electrodes achieve considerable power conversion efficiencies of 13.15%, 13.03%, and 12.83% for blue, green, and red devices, respectively.

Organic solar cells (OSCs) own unique advantages such as solution process, low cost, mechanical flexibility, and colorful semitransparency, making them preferable candidates to realize building-integrated photovoltaics. To meet the requirements of architectural aesthetics, the Fabry–Perot micro-cavity electrode is a good choice to achieve flexible color tunability. Herein, a Ag/MgF₂/Ag micro-cavity is constructed to act as a spectral selective transmission electrode. The micro-cavity electrodes demonstrate high peak transmittance in specific wavelengths (blue, green, and red) by adjusting the thickness of dielectric layer MgF₂, enabling the optimized colorful OSCs with blue, green, and red colors to exhibit high power conversion efficiencies of 13.15%, 13.03%, and 12.83% with peak transmittance of 35.5%, 33.7%, and 21.9%, respectively. Impressive results imply that our Ag/MgF₂/Ag micro-cavity electrodes possess great potential in practical colorful semitransparent OSCs applications.

The high-valence Eu³⁺ was applied in carbon-based printable mesoscopic inorganic CsPbBr₃ perovskite solar cells (PSCs) for the first time. The high open-circuit voltage and stability of the device demonstrate that the CsPbBr₃ PSC is a promising device to drive the water electrolysis device.

The all-inorganic CsPbBr₃ perovskite exhibits the possibility of overcoming the substantial nonideal thermal, humidity, and photostability of hybrid organic–inorganic perovskite solar cells (PSCs) in photoelectronic devices. Specifically, the rapid development of CsPbBr₃ perovskite has delivered device efficiencies >10%. However, the mismatched energy band alignment and bad crystallization quality are still potential obstacles for the superior performance of PSCs. Herein, by employing n-type doping, trivalent europium cation is successfully introduced into the CsPbBr₃ lattice. The better energy-level alignment leads to further reduction of voltage losses. Besides, the large and uniform grains resulting from the improvement of crystallization after doping decrease the grain boundaries and reduce the nonradiative recombination center. The quality of the film improves substantially, which significantly enhances the photoabsorption and the short-circuit current density. The efficiency of the carbon-based printable mesoscopic PSCs is improved from 7.5% to 8.06% with 3 mol% Eu³⁺ doping, resulting in high open-circuit voltage of 1.41 V. Based on the device with effective area of 1 cm² and 60.075 cm², the record power conversion efficiency of 5.41% and 1.14% is obtained. The device also displays excellent stability with driving water electrolysis.

Herein, fabrication of 2D-perovskite films with narrow phase distribution is reported. Introducing 3-amino-4-phenol-sulfonic acid additive into the precursor forms an intermediate through strong coordination between –SO₃H group and Pb²⁺, allowing preferential self-assembly of vertically-oriented n = 3 and 4 phases. A photovoltaic efficiency of 14.34%, open-circuit voltage of 1.20 V and excellent ambient stability (T ₉₆) of 1440 h are achieved.

2D Ruddlesden–Popper perovskites have risen to prominence as stable and efficient photovoltaic materials because of their structural diversity, rich photophysics, and low moisture ingression. However, thin films processed from stoichiometric precursor solutions possess a broad phase distribution of different number of inorganic layers with random crystal orientation, crippling device performance. The effect of methylammonium chloride (MACl) and 3-amino-4-phenolsulfonic acid (APSA) on the fabrication of perpendicularly oriented (PEA)₂MA₄Pb₅I₁₆ films with narrow phase distribution using antisolvent and hot-casting processing techniques is investigated. MACl plays a critical role in suppressing parasitic n ≤ 2 and 3D-like phases. APSA performs the dual function of trap passivation and further narrowing phase polydispersity through strong coordination with Pb²⁺. Ex situ grazing-incident wide-angle X-Ray scattering (GIWAXS) and ultrafast spectroscopic characterization reveal uniformly mixed-phase distribution with disordered orientation in antisolvent treated films, while additive-assisted hot-casting treatment results in oriented, reverse-graded phase distribution, i.e., small-n on the film surface and large-n at the bottom. Arising thin films enable efficient p–i–n solar cells with an efficiency of 14.34%, and a V _oc of 1.20 V, retaining 96% initial efficiency after 1440 h under ambient conditions (RH = 50–60%) without encapsulation.

The poly[4,8-bis(5-(2-hexyldecyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene][5,5′-bis(7-(4-(2-butyloctyl)thiophen-2-yl)-6-fluorobenzo[c][1,2,5]thiadiazol-4-yl)-2,2′-bithiophene] (PDBD-FBT) polymer is used as a donor material for organic photovoltaics by the advantage of increasing crystallinity and improving face-on packing when the thermal treatment is applied on regioregular polymers. These characteristics are proved by the improved photoconversion efficiency and thickness tolerance of the organic photovoltaics.

To successfully develop a regioregular polymer, poly[4,8-bis(5-(2-hexyldecyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene][5,5′-bis(7-(4-(2-butyloctyl)thiophen-2-yl)-6-fluorobenzo[c][1,2,5]thiadiazol-4-yl)-2,2′-bithiophene] (PDBD-FBT), a symmetric monomer synthesized in high yield by tin homo-coupling reactions. PDBD-FBT is suitable as a donor material in organic photovoltaics (OPVs) because it shows high crystallinity and strong face-on packing properties. These properties were amplified by thermal annealing (TA). This causes a power conversion efficiency (PCE) enhancement in PDBD-FBT-based OPVs. Using PDBD-FBT as a polymer donor and 2,2′-((2Z,2′Z)-((12,13-bis(2-heptylundecyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2″,3″:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno[2′,3′:4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (Y6-HU) as an electron acceptor, a PCE of 7.91% was achieved without any additive and TA at optimized active layer film thickness of approximately 100 nm. After TA, a PCE of 12.53% was achieved with a 58% increase compared with the reference devices. Owing to the strong crystallinities, trap-assisted recombination occurs by excessively formed grain boundaries; however, efficient exciton dissociation sufficiently covers these drawbacks. Even in the approximately 340 nm-thick film condition, this tendency is more pronounced (73% PCE enhancement is observed from 6.17% to 10.69% of PCE in the without and with TA devices, respectively). Our study demonstrates that it is possible to manufacture thickness-insensitive OPVs based on regioregular polymers with strong crystallinity and face-on characteristics, thereby providing a solution to the thickness variation of large-area organic solar cell modules.

PCE of 16.35% is achieved in ternary polymer solar cells (PSCs) with D18-Cl:Y11:Y5 as photoactive layers. The good compatibility and similar lowest unoccupied molecular orbital levels of Y11 and Y5 enable the formation of the alloyed state for efficient electron transport in ternary photoactive layers. Energy transfer from Y5 to Y11 should improve the exciton utilization in ternary blend PSCs.

Ternary polymer solar cells (PSCs) consist of two structurally similar fullerene-free small molecules as acceptors (Y11 and Y5), and D18-Cl as polymer, which have better photovoltaic performance relative to D18-Cl:Y11 binary PSC. The enhanced photovoltaic performance of the binary PSCs is mainly attributed to the significantly enhanced short circuit current density (J _SC) and slightly enhanced fill factor. The enhanced J _SC value is due to the 45 nm blueshift of the absorption peak of Y5 relative to Y11, which facilitates more efficient absorption of photons in the visible light-wavelength band. Another reason for the enhanced J _SC is the efficient charge transport and reduced exciton coupling. Meanwhile, the Y5 film has higher crystallinity and smaller lamellar spacing and π–π stacking distance relative to the Y11 film, and 35% of Y5 instead of Y11 is beneficial to improve the surface morphology, phase separation size, and crystallinity of the ternary photoactive layer. Therefore, the best ternary PSC shows higher open-circuit voltage values relative to the D18-Cl:Y6 binary reference PSC and higher J _SC values relative to the D18-Cl:Y11 binary PSC. Thus, blend fullerene-free small molecules with similar molecular structures and different optical and electronic properties as acceptor materials are new insights for the development of ternary PSCs.

Solvent engineering is a new paradigm for improving the efficiency and stability of perovskite solar cells (PSCs). The incorporation of a pure-solvent interlayer between the SnO₂ electron transport layer and perovskite can increase the PSC efficiency, as an effective strategy for interfacial engineering of PSCs.

Interfacial engineering is extensively used to reduce the interfacial loss caused by surface recombination, improve the crystallinity of the active absorption layer, and enhance the long-term stability of perovskite solar cells (PSCs). Solution processing techniques, such as spin coating and dip coating, are commonly used to deposit the interfacial layer because of their cost-effectiveness and simplicity. Although determining suitable solutes for use in these processes is important, selecting appropriate solvents is also crucial. Herein, commonly used solvents are investigated to determine optimal solvents for solution processing by categorizing them into nonpolar and polar groups. The results suggest that the efficiency of the PSCs can be increased by simple solvent treatment. In particular, the efficiencies of systems subjected to hexane (nonpolar) and ethanol (polar) treatment are significantly improved (17.31% and 17.44%, respectively) compared with that of a control device (16.24%). Herein, the effects of pure solvents on the SnO₂–perovskite interface are confirmed and an important direction for investigations that adopt solution processing to improve the efficiency of PSCs, such as research on interlayers and self-assembled monolayers, is suggested.

The composition of perovskite materials is regulated based on its ion migration characteristics. It is found that the codoping of appropriate methylammonium and Cs cation in the formamidinium-rich perovskite is favorable for highly efficient and stable perovskite solar cells. The optimized triple-cation FA_0.90Cs_0.04MA_0.06PbI₃ devices maintain 87% of the initial efficiency after operating for 1800 h.

The degradation of the perovskite solar cells (PSCs) is closely related to phase decomposition, phase separation, and structural collapse, which mainly originates from the intrinsic ion migration under light soaking and thermal stress. Herein, the composition of perovskite materials is regulated based on its ion migration characteristics. By systematically studying the effect of A-site cations on the ion migration and photothermal stability of organic–inorganic hybrid perovskite materials, it is found that the codoping of appropriate methylammonium (MA) and Cs cation in the formamidinium (FA)-rich perovskite is favorable for the highly efficient and stable PSCs. The optimized triple-cation FA_0.90Cs_0.04MA_0.06PbI₃ exhibits significantly improved photothermal stability in comparison with the double-cation and Br-containing perovskite materials. Moreover, the optimized triple-cation device demonstrates excellent operation stability at maximum power tracking, and maintains 87% of initial efficiency after 1800 h.

Herein, an optimization strategy of electron transport layer based on hydrogen bond is proposed. 1,8-Octanediol (DOH) can form hydrogen bonds with PDINN, which reduces the work function of the electrode and optimizes the carrier transport process, so that the binary all-small-molecule organic solar cells obtain a high power conversion efficiency (PCE) of 15.88% with enhanced thermal stability.

All-small-molecule organic solar cells (ASM-OSCs) have the advantages of simple structure, easy purification, and small-batch variation, thus showing broad prospects for commercialization. However, less research has been conducted on the transport layer of ASM-OSCs, resulting in a low match between the active and transport layers, which limits the increase of the power conversion efficiency (PCE) of the device. Therefore, an electron transport layer (ETL) optimization strategy is proposed to improve device performance by introducing 1,8-Octanediol (DOH) into the conventional ETL of PDINN to form intermolecular hydrogen bonds, which can reduce the work function of the electrode and accelerate the electron transport. By depositing the optimized ETL on BTR-Cl:Y6-based active layer, the ASM-OSC achieves a champion PCE of 15.88% with excellent thermostability. Moreover, DOH-doped PDINN endows the ASM-OSC with good tolerance to the film thickness of the ETL. When the thickness of the ETLs is increased from 10 to 50 nm, the PCE of the optimized device still maintains at 81.68% of the highest value, demonstrating great potential for large-area and industrial production. These results suggest that the hydrogen bond-based interface optimization strategy is a simple and efficient way to enhance the performance of ASM-OSCs.

The crab-shape molecule named BCP-3N is synthesized to chelate with insufficiently coordinated Pb ions in perovskite films. In synergy with the green antisolvent ethanol (EtOH) to orient the growth of perovskite, the internal stability and power conversion efficiency (PCE) of inverted perovskite solar cells are simultaneously improved, with a record PCE of 20.98% using alcohol as polar antisolvent.

Defects at the perovskite grain boundaries and the interfaces between perovskite and charge transport layers in perovskite solar cells (PSCs) are a curse of nonradiative recombination losses and device degradation channels. Herein, the custom design and synthesis of a multifunctional small molecule (N ²,N ⁹-bis(3-(dimethylamino)propyl)-4,7-diphenyl-1,10-phenanthroline-2,9-dicarboxamide (BCP-3N) featured by the π-conjugated phenanthroline and an array of lone-pair electron donor atoms from the carbonyl and amine groups are reported. The BCP-3N is used as a Lewis base to multidentate passivate the undercoordinated Pb²⁺ ions forming an ultrathin tunnel layer, in synergy with ethanol as a green antisolvent to simultaneously orient the growth of perovskite, resulting in a significantly reduced defect density in perovskite films. With BCP-3N, a significant increase in open-circuit voltage (V _oc = 1.12 V) is achieved of inverted (p–i–n structure) PSCs, along with a record power conversion efficiency of ≈21% among alcohol antisolvent processed cells. Also, attested are a much higher illumination and humidity stability of the BCP-3N-based device. Combined experimental and theoretical studies have uncovered the multifunctional roles of BCP-3N in stabilizing high-quality Cs–FA–MA triple-cation mixed perovskites under light, bias, and humidity stresses, enlightening the molecular design for PSCs.

A bottom-up multifunctional modification strategy, which is implemented in introducing Lewis base ligand molecules containing different carbonyl numbers into SnO₂ colloidal solution, is developed. The modified device achieves an impressive efficiency up to 23.35%, which is significantly higher than 21.59% of the reference device.

The defects of perovskite and SnO₂ layers, interfacial energy barrier, and high grain boundary density impede further development of perovskite solar cells. Herein, a bottom-up versatile modification strategy, which is implemented via introducing Lewis base ligand molecules containing different numbers of carbonyls (urea, propanedioic acid, and barbituric acid [BA]) into SnO₂ colloidal solution, is reported. All modifiers exhibit positive but different defect passivation effects for both SnO₂ and perovskite layers. The defect passivation effect can be rationally modulated by tuning the number of carbonyls and is directly proportional to the number of carbonyls. The enlargement sequence of the grain size is the same as that of the defect passivation effect. Meanwhile, the interfacial energy barrier, charge accumulation, and hysteresis are mitigated after modification, which is principally attributed to improved energy band alignment, reduced interfacial defects, and improved electrical properties of SnO₂ films. The BA-modified device achieves an impressive efficiency up to 23.35%, which is significantly higher than 21.59% of the reference device. In addition, the modified devices demonstrate enhanced moisture and thermal stabilities.

Semitransparent organic solar cells offer potentially more opportunities in areas of self-powered greenhouses and building-integrated photovoltaic systems. The use of a combination of solution-processable gold nanobipyramids-based hole transporting layer and a low/high dielectric constant double layer optical coupling layer for improving the cell performance over the two competing indexes of power conversion efficiency and average visible transmittance is reported.

Abstract

Semitransparent organic solar cells (ST-OSCs) offer potentially more opportunities in areas of self-powered greenhouses and building-integrated photovoltaic systems. In this work, the effort to use a combination of solution-processable gold nanobipyramids (AuNBPs)-based hole transporting layer and a low/high dielectric constant double layer optical coupling layer (OCL) for improving the performance of ST-OSCs over the two competing indexes of power conversion efficiency (PCE) and average visible transmittance (AVT) is reported. The fabrication and characterization of the ST-OSCs are guided, at design and analyses level, using the theoretical simulation and experimental optimization. The use of a low/high dielectric constant double layer OCL helps enhancing the visible light transparency while reflecting the near-infrared (NIR) photons back into the photoactive layer for light harvesting. NIR absorption enhancement in the ST-OSCs is realized through the AuNBPs-induced localized surface plasmon resonance (LSPR). The weight ratio of the polymer donor to nonfullerene acceptor in the bulk heterojunction is adjusted to realize the maximum NIR absorption enhancement, enabled by the AuNBPs-induced LSPR, achieving the high-performance ST-OSCs with a high PCE of 13.15% and a high AVT of 25.9%.

BDA can make full use of the two ammonium cations for passivation and strengthen the absorption of BDA onto the V _FA defect as well as enhance the formation energy of V _FA, and thereby anchor the perovskite surfaces, so as to improve the photovoltaic performance of rigid and flexible devices.

Abstract

Organic ammonium salts have been widely used for defect passivation to suppress nonradiative charge recombination in perovskite solar cells (PSCs). However, they are prone to form undesirable in-plane favored 2D perovskites with poor charge transport capability that hamper device performance. Herein, the defects passivation role of alkyldiammonium including 1.6-hexamethylenediamine dihydriodide (HDAI₂), 1,3-propanediamine dihydriodide (PDAI₂), and 1.4-butanediamine dihydriodide (BDAI₂) for formamidinium-cesium perovskite is systematically investigated. With help of density functional theory (DFT) calculations, BDA with suitable size can synergistically passivate two defect sites on perovskite surfaces, showing the best defect passivation effect among the above three alkyldiammonium salts. Perovskite films based on BDAI₂ modification are found to keep the 3D perovskite phase with considerably reduced trap-state density, and enhanced carrier extraction. As a result, the BDAI₂-modified devices deliver impressive efficiencies of 23.1% and 20.9% for inverted PSCs on the rigid and flexible substrates, respectively. Moreover, the corresponding encapsulated rigid devices maintain 92% of the initial efficiency after operating under continuous 1-sun illumination with the maximum power point tracking for 1000 h. Furthermore, the mechanical flexibility of the BDAI₂-modified flexible device is also improved due to the release of residual stress.

A pyridine-functionalized fullerene derivative, fullerene-n-butyl-pyridine (C₆₀-BPy), is developed to functionalize the interface between the tin perovskite and C₆₀ electron transport layer, which can simultaneously achieve defect passivation and energy level adjustment. The resulting devices have achieved the highest PCE of 14.14% with excellent light and heat stability.

Abstract

In tin perovskite solar cells (PSCs), fullerene (C₆₀) and fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are commonly utilized electron transport materials. However, the energetic disorder, inadequate passivation, and energy level mismatch of C₆₀ and PCBM limit the improvement of power conversion efficiency (PCE) and lifespan of tin PSCs. In this work, a multifunctional interface manipulation strategy is developed by introducing a pyridine-functionalized fullerene derivative, fullerene-n-butyl-pyridine (C₆₀-BPy), into the interface between the tin perovskite and the electron transport layer (ETL) to improve the photovoltaic performance and stability of tin PSCs. The C₆₀-BPy can strongly anchor on the perovskite surface via coordination interactions between the pyridine moiety and the Sn²⁺ ion, which not only reinforces the passivation of the trap-state within the tin perovskite film, but also regulates the interface energy level alignment to reduce non-radiative recombination. Moreover, the improved interface binding and carrier transport properties of C₆₀-BPy contribute to superior device stability. The resulting devices have achieved the highest PCE of 14.14% with negligible hysteresis, and are maintained over 95% of their initial PCE under continuous one-sun illumination for 1000 h.