JIALINGBO

Addition of dual additive of methylammonium chloride (MACl) and CsCl in the FAPbI₃ perovskite precursor solution with a molar ratio of [MACl]/[CsCl] = 2 results in a higher power conversion efficiency and better stability than the single additive, due mainly to the further reduction in trap density and increase in resistance for charge recombination.

Abstract

Additive engineering is one of the most efficient approaches to improve not only photovoltaic performance but also phase stability of formamidinium (FA)-based perovskite. Chlorine-based additives, such as methylammonium chloride (MACl), have been in general used to improve phase stability of FAPbI₃, which however often leads to loss of open-circuit voltage V _oc, accompanied by instability of the perovskite phase due to the volatile nature of the MA cation. A dual additive strategy for improving V _oc and thereby the overall efficiency are reported here. The mixing ratio of MACl to CsCl is varied from [MACl]/[CsCl] = 4 to 1, where V _oc increases with decreasing the ratio and best performance is achieved from [MACl]/[CsCl] = 2. As compared to the single source of MACl, the addition of CsCl reduces trap density and increases resistance against charge recombination, which is responsible for the increased V _oc. Moreover, defect passivation achieved by dual additive enables better stability than the single additive MACl as confirmed by long-term stability tests with unencapsulated devices for 50 days under relative humidity of about 40% at room temperature. The best power conversion efficiency of 23.22% is achieved by dual additive, which is higher than that for single additive of MACl or CsCl.

A fatigue‐free layered hybrid perovskite ferroelectric, (C₆H₅CH₂NH₃)₂CsPb₂Br₇, is demonstrated for exploration of photovoltaic non‐volatile memories.

Abstract

Through a functional unit‐transmutation strategy, a fatigue‐free layered hybrid perovskite ferroelectric (C₆H₅CH₂NH₃)₂CsPb₂Br₇ (BCPB) has been developed, which demonstrates stable spontaneous polarization (P _s) of 6.5 μC cm⁻² and high Curie temperature up to 425 K. Meanwhile, BCPB shows splendid bulk photovoltaic effect (BPVE) properties with noticeable zero‐bias photocurrent density (5 μA cm⁻²), and high on/off switching ratio of current (over 3×10⁵); these merits even overmatch the most known ferroelectric semiconductor BiFeO₃. The unique structure with self‐regulated net electrical charged layers gives rise to the fatigue‐free feature of P _s and BPVE (no significant fatigue after 10⁸ polarity switching cycles), promoting the potential applications of BCPB in photovoltaic non‐volatile memories. This work offers an efficient approach for exploring fatigue‐free semiconducting ferroelectrics as well as excavates their further applications in next‐generation electronic devices.

An organic small-molecule semiconductor, DPh-DNTT, can be utilized as a dopant-free hole transporting material (HTM) for highly efficient and stable inverted perovskite solar cells due to its temperature-dependent molecular orientation. By decreasing the deposition temperature, DPh-DNTT films with a dominant face-on orientation are achieved, which exhibit improved out-of-plane hole mobility and excellent perovskite device performance without the incorporation of double-edged dopants.

Abstract

Crystallized p-type small-molecule semiconductors have great potential as an efficient and stable hole transporting materials (HTMs) for perovskite solar cells (PSCs) due to their relatively high hole mobility, good stability, and tunable highest occupied molecular orbitals. Here, a thienoacene-based organic semiconductor, 2,9-diphenyldinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DPh-DNTT), is thermally evaporated and employed as the dopant-free HTM that can be scaled up for large-area fabrication. By controlling the deposition temperature, the molecular orientation is modulated into a dominant face-on orientation with π–π stacking direction perpendicular to the substrate surface, maximizing the out-of-plane carrier mobility. With an engineered face-on orientation, the DPh-DNTT film shows an improved out-of-plane mobility of 3.3 × 10⁻² cm² V⁻¹ s⁻¹, outperforming the HTMs reported so far. Such orientation-reinforced mobility contributes to a remarkable efficiency of 20.2% for CH₃NH₃PbI₃ inverted PSCs with enhanced stability. The results reported here provide insights into engineering the orientation of molecules for the dopant-free organic HTMs for PSCs.

MAPbI₃ crystal growth in the films made by drop‐casting is regulated by changing the temperature. At low temperature (60 °C), the crystals are (110) oriented, needle‐like. At high temperature (>120 °C), the crystals are (200) oriented, presenting round grains. The different crystal growth mode leads to quite different film morphology and photovoltaic performance.

Abstract

Drop‐casting was used to make MAPbI₃ films for solar cells. The crystal growth in drop‐cast MAPbI₃ films was regulated by adjusting temperature. A mechanism for the formation of different morphology was proposed by combining in situ crystal‐growth study with XRD measurements. The crystals in the films made at low temperature (60 °C) and high temperature (≥120 °C) are (110) and (200) oriented, respectively. The different crystal growth mode leads to quite different film morphology. Compared with spin‐coating, drop‐casting shows much better tolerance to humidity. MAPbI₃ solar cells made under 88 % humidity delivered a PCE of 18.17 %, which is the highest PCE for perovskite solar cells made under >70 % humidity without antisolvent assistance.

Thermodynamically stable β‐CsPbI₃ nanocrystals are prepared, and they are demonstrated to function as a stable, efficient red‐emitting layer. With incorporation of poly(maleic anhydride‐alt‐1‐octadecene), the β‐CsPbI₃ further exhibits reduced deep defects of Pb_Cs, increased exciton binding energy, and reduced longitudinal‐optical phonon energy. Red‐emitting perovskite light‐emitting diodes (PeLEDs) based on β‐CsPbI₃ achieve both high external quantum efficiency and superior operational stability.

Abstract

The long‐term operational stability of perovskite light‐emitting diodes (PeLEDs), especially red PeLEDs with only several hours typically, has always faced great challenges. Stable β‐CsPbI₃ nanocrystals (NCs) are demonstrated for highly efficient and stable red‐emitting PeLEDs through incorporation of poly(maleic anhydride‐alt‐1‐octadecene) (PMA) in synthesizing the NCs. The PMA can chemically interact with PbI₂ in the precursors via the coupling effect between O groups in PMA and Pb²⁺ to favor crystallization of stable β‐CsPbI₃ NCs. Meanwhile, the cross‐linked PMA significantly reduces the Pb_Cs anti‐site defect on the surface of the β‐CsPbI₃ NCs. Benefiting from the improved crystal phase quality, the photoluminescence quantum yield for β‐CsPbI₃ NCs films remarkably increases from 34% to 89%. The corresponding red‐emitting PeLEDs achieves a high external quantum efficiency of 17.8% and superior operational stability with the lifetime, the time to half the initial electroluminescence intensity (T ₅₀) reaching 317 h at a constant current density of 30 mA cm⁻².

B-site substituted 2D Ca₂Nb_{3− x} Ta _x O₁₀ (x = 0, 0.5, 1, 1.5) perovskite oxides are successfully prepared by liquid exfoliation. The photodetectors based on them exhibit a tunable spectral response with the change of the Ta content. The Ca₂Nb_2.5Ta_0.5O₁₀ photodetector outperforms other samples, exhibiting a boosted responsivity compared to pristine Ca₂Nb₃O₁₀ photodetector due to the trap-induced high photoconductive gain.

Abstract

2D Dion-Jacobson perovskite oxides, featuring fascinating optical and electric properties, exhibit great potential in optoelectronic devices. However, the device sensitivity and spectral selectivity are limited. Herein, B-site substituted calcium niobate Ca₂Nb_{3− x} Ta _x O₁₀ (x = 0, 0.5, 1, 1.5) nanosheets are prepared by liquid exfoliation. The photodetectors (PDs) based on these nanosheets exhibit tunable spectral response by tailoring the band gap of the nanosheets. All the Ta-substituted PDs show increased photocurrent and enhanced responsivity, among which the Ca₂Nb_2.5Ta_0.5O₁₀ PD exhibits the optimal performance with a photocurrent of 31.4 µA, a high on–off ratio of 5.6 × 10⁴ and a boosted responsivity of 469.5 A W⁻¹ at 1.0 V toward 295 nm, which is over 7000-fold higher than that of pristine Ca₂Nb₃O₁₀ PD. It is proposed that the significantly optimized responsivity is ascribed to the enhanced photoconductive gain that mainly originates from the introduction of the trap states by the B-site substitution. Nevertheless, excess substitution is detrimental to the responsivity and the response speed. This work demonstrates that the rational control of B-site substitution tailors the band gap and modulates the charge-carrier behaviors in 2D perovskite oxides, which provides an effective avenue for achieving high-performance PDs with tunable spectral response and excellent responsivity.

Herein, a coordination strategy is reported for the formation of a highly compact CuSCN hole-transporting layer by retarding fast crystallization via constructing intermediate adducts. CuSCN thin films prepared from a unique intermediate adduct CuSCN-(Cl-Py) show a high quality, which facilitates efficient hole extraction and suppressed charge recombination in perovskite solar cells, resulting in an enhanced device efficiency.

The preparation of a high-quality CuSCN thin film is very important to guarantee its efficient performance in an electronic device. Herein, a coordination strategy is reported for the formation of a highly compact CuSCN hole-transporting layer by retarding fast crystallization via constructing intermediate adducts, and investigated its application for perovskite solar cells (PSCs). Specifically, the strong coordination bond between CuSCN and pyridine derivate ligands results in the formation of a stable intermediate phase, which is further converted to compact CuSCN layers under thermal annealing. The configuration of the intermediate phase is demonstrated to be crucial for the subsequent assembly of high-quality CuSCN layers and results in an improved performance of the devices. CuSCN thin films crystallized from an intermediate adduct, CuSCN-(Cl-Py), with a rippled sheet configuration show an exceptional surface uniformity and high hole mobility, which facilitates efficient hole extraction and suppresses charge recombination in PSCs, resulting in an enhanced device efficiency of 19.19%. That is the highest value of the inverted planar PSCs using CuSCN as a hole-transporting layer to the best of the authors’ knowledge. This novel coordination strategy can be expected to be used in the preparation of other inorganic charge transporting materials for electronic devices.

Nanoscale photovoltaic characterization of a hybrid organic–inorganic halide perovskite solar cell reveals an elevated open-circuit voltage and suppressed short-circuit photocurrent near grain boundaries. Complementary ionic strain and surface potential mapping indicate that these photovoltaic properties are associated with local ion accumulation and band bending.

Abstract

Although hybrid organic–inorganic halide perovskite solar cells have achieved extraordinary improvements over the past few years, questions remain about the role of grain boundaries. This article reports on the nanoscale point-by-point current–voltage mapping of photovoltaic characteristics in inverted methylammonium lead triiodide perovskite solar cells. These measurements reveal an increased open-circuit voltage and shunt resistance, along with a suppressed short-circuit photocurrent at grain boundaries and nearby regions. Support from nanoscale ionic strain and surface potential mapping suggests that local ion accumulation and downward band bending can facilitate charge separation, but hinder charge collection at grain boundaries.

Perovskite Solar Cells

In article number 2000621, Wei Wang, Zongping Shao, and co‐workers introduced a gentle butyl acrylate additive into MAPbI₃‐based perovskite solar cells to enhance the efficiency and stability by improving perovskite film quality, constructing suitable energy level alignment and increasing charge carrier lifetime. Consequently, the device with butyl acrylate additive delivers a high power conversion efficiency of 20.0% and superior moisture/thermal stability under ambient conditions.

A facile yet effective thioamides passivation strategy is proposed to suppress defects at the surface and grain boundary of CsSnI₃ perovskite, which reduces the deep level trap density from undercoordinated Sn²⁺ and Sn²⁺ oxidation. The surface passivated CsSnI₃ perovskite solar cell (PSC) delivers a efficiency of 8.20% which is the highest among all lead‐free all‐inorganic PSCs.

Abstract

Despite remarkable progress in hybrid perovskite solar cells (PSCs), the concern of toxic lead ions remains a major hurdle in the path towards PSC's commercialization; tin (Sn)‐based PSCs outperform the reported Pb‐free perovskites in terms of photovoltaic performance. However, it is of a particularly great challenge to develop effective passivation strategies to suppress Sn(II) induced defect densities and oxidation for attaining high‐performance all‐inorganic CsSnI₃ PSCs. Herein, a facile yet effective thioamides passivation strategy to modulate defect state density at surfaces and grain boundaries in CsSnI₃ perovskites is reported. The thiosemicarbazide (TSC) with SCN functional groups can make strong coordination interaction with charge defects, leading to enhanced electron cloud density around defects and increased vacancy formation energies. Importantly, the surface passivation can reduce the deep level trap state defect density originated from undercoordinated Sn²⁺ ion and Sn²⁺ oxidation, significantly restraining nonradiative recombination and elongating the carrier lifetime of TSC treated CsSnI₃ PSCs. The surface passivated all‐inorganic CsSnI₃ PSCs based on an inverted configuration delivers a champion power conversion efficiency (PCE) of 8.20%, with a prolonged lifetime over 90% of initial PCE, after 500 h of continuous illumination. The present strategy sheds light on surface defect passivation for achieving highly efficient all‐inorganic lead‐free Sn‐based PSCs.

Half‐mixed Pb‐Sn perovskite solar cells with significantly improved performance and stability are prepared by introducing an ionic imidazolium tetrafluoroborate additive. The synergistic effects of IM cation and tetrafluoroborate anion enable efficient defect passivation at grain boundaries, reducing leakage current, and enlargement in grain size with relaxed lattice strain simultaneously, thereby exerting a remarkable impact on device performance and stability.

Abstract

Narrow‐bandgap mixed Pb‐Sn perovskite solar cells (PSCs) have great feasibility for constructing efficient all‐perovskite tandem solar cells, in combination with wide‐bandgap lead halide PSCs. However, the power conversion efficiency of mixed Pb‐Sn PSCs still lags behind lead‐based counterparts. Here, additive engineering using ionic imidazolium tetrafluoroborate (IMBF₄) is proposed, where the imidazolium (IM) cation and tetrafluoroborate (BF₄) anion efficiently passivate defects at grain boundaries and improve crystallinity, simultaneously relaxing lattice strain, respectively. Defect passivation is achieved by the chemical interaction between the IM cation and the positively charged under‐coordinated Pb²⁺ or Sn²⁺ ions, and lattice strain relaxation is realized by lattice expansion with the intercalation of BF₄ anions into the perovskite lattice. As a result, the synergistic effects of the cation and anion in the IMBF₄ additive greatly enhance the optoelectronic performance of half‐mixed Pb‐Sn perovskites, leading to much longer carrier lifetimes. The best‐performing half‐mixed Pb‐Sn PSC shows an efficiency above 19% with negligible hysteresis, while retaining over 90% of its initial efficiency after 1000 h in a nitrogen‐filled glovebox and showing a lifetime to 80% degradation of 53.5 h under continuous illumination.

Perovskite single crystals (PVSK SCs) without detrimental grain boundaries and defects possess orders of magnitude larger diffusion length, carrier lifetime, and lower trap density in comparison with PVSK polycrystalline films. In this review, the recent progress of synthesis methods of PVSK SCs and their application in optoelectronic devices is summarized.

Abstract

Recently, lead halide perovskite (PVSK) polycrystalline films have drawn much attention as photoactive material and scored tremendous achievements in solar cells, photodetectors, light‐emitting diodes, and lasers owing to their engrossing optoelectronic properties and facile solution‐processed fabrication. However, large amounts of grain boundaries unfavorably induce ion migration, surface defect, and poor stability, impeding PVSK polycrystalline film‐based optoelectronic devices from practical application. In comparison with the polycrystalline counterparts, PVSK single crystals (SCs) with lower trap density serve as a better platform for not only fundamental research but also device applications. In light of this, the idea of using PVSK single crystals (SCs) to construct the optoelectronic devices is then proposed. Since then, a series of synthesis methods of PVSK SCs have emerged. In this review, recent progress of synthesis method of PVSK SCs is tried to be summarized and their advantages and limitations are analyzed. And then, the optoelectronic properties including carrier dynamic, defects, ion migration, and instability issues in these 3D and 2D PVSK SCs are overviewed and accordingly the proper device configurations of corresponding solar cells, photodetectors, X‐ray, γ‐ray detectors, etc., are proposed. It is believed that this review can provide the guidance for the further development of PVSK SCs and their applications.

Moisture instability and unscalable fabrication protocols remain unsolved issues that hinder the application of FACs‐based perovskite solar cells. Here, high‐quality FACsPbI₃ films are fabricated by crown ether tailoring (which chelated with Cs⁺/Pb²⁺ ions) to inhibit the moisture invasion and stabilize the a ‐phase FACsPbI₃, producing large‐area perovskite films and with solar module performance.

Abstract

FACs‐based (FA⁺, formamidinium and Cs⁺, cesium) perovskite solar cells have gained great attention due to their remarkable light and thermal stabilities toward practical application of perovskite modules. However, the moisture instability and difficulty in scalable fabrication are still the main obstacles blocking their photovoltaic applications in current status. Here, the employment of novel interaction between crown ether with metal cations is introduced to tailor the uniform growth and inhibit moisture invasion during the crystallization of α‐phase FACsPbI₃, yielding the successful synthesis of high‐quality perovskite films in a large scale. Consequently, perovskite solar cells (PSC) modules in the total area of 4 × 4 and 10 × 10 cm² are readily fabricated with respective champion efficiencies of 16.69% and 13.84% and excellent stability over 1000 h. This facile scaling‐up strategy assisted by crown ether has shown great promise for pursuing efficient and highly stable large‐area PSC modules.

The potential of wide bandgap perovskite solar cells is often limited by low open‐circuit voltages. By tuning the lowest‐unoccupied molecular‐orbital of electron transport layers via the use of different fullerenes and fullerene blends, open‐circuit voltages exceeding 1.35 V in CH₃NH₃Pb(I_0.8Br_0.2)₃ device without loss in fill factor leading to a high V _oc FF product of 1.10 V are demonstrated.

Abstract

Nonradiative recombination processes are the biggest hindrance to approaching the radiative limit of the open‐circuit voltage for wide bandgap perovskite solar cells. In addition to high bulk quality, good interfaces and good energy level alignment for majority carriers at charge transport layer‐absorber interfaces are crucial to minimize nonradiative recombination pathways. By tuning the lowest‐unoccupied molecular‐orbital of electron transport layers via the use of different fullerenes and fullerene blends, open‐circuit voltages exceeding 1.35 V in CH₃NH₃Pb(I_0.8Br_0.2)₃ device are demonstrated. Further optimization of mobility in binary fullerenes electron transport layers can boost the power conversion efficiency as high as 18.9%. It is noted in particular that the V _oc fill factor product is >1.096 V, which is the highest value reported for halide perovskites with this bandgap.

A facile strategy of employing an acceptor‐analogue is developed to efficiently reduce trap density to a magnitude of 10¹⁵ cm⁻³ for organic photovoltaic materials, which is comparable to and even lower than those of some inorganic counterparts, and boosts the power conversion efficiency of organic solar cells up to 17.8%.

Abstract

Typical organic semiconductor materials exhibit a high trap density of states, ranging from 10¹⁶ to 10¹⁸ cm⁻³, which is one of the important factors in limiting the improvement of power conversion efficiencies (PCEs) of organic solar cells (OSCs). In order to reduce the trap density within OSCs, a new strategy to design and synthesize an electron acceptor analogue, BTPR, is developed, which is introduced into OSCs as a third component to enhance the molecular packing order of electron acceptor with and without blending a polymer donor. Finally, the as‐cast ternary OSC devices employing BTPR show a notable PCE of 17.8%, with a low trap density (10¹⁵ cm⁻³) and a low energy loss (0.217 eV) caused by non‐radiative recombination. This PCE is among the highest values for single‐junction OSCs. The trap density of OSCs with the BTPR additives, as low as 10¹⁵ cm⁻³, is comparable to and even lower than those of several typical high‐performance inorganic/hybrid counterparts, like 10¹⁶ cm⁻³ for amorphous silicon, 10¹⁶ cm⁻³ for metal oxides, and 10¹⁴ to 10¹⁵ cm⁻³ for halide perovskite thin film, and makes it promising for OSCs to obtain a PCE of up to 20%.

A moiré interference structure augments light‐diffraction channels, leading to elongated optical paths, and “folds” sunlight into the perovskite layer. Besides, the sets of moiré diffracted light achieve “1 + 1 = 3” comparing to the single diffraction grating. Therefore, moiré perovskite solar cells are constructed by way of a commercial DVD disc, resulting in a champion efficiency up to 20.17% (MAPbI₃) and 21.76% ((FAPbI₃)_{1‐ x} (MAPbBr₃) _x ).

Abstract

Light harvesting is crucial for thin‐film solar cells. To substantially reduce optical loss in perovskite solar cells (PSCs), hierarchical light‐trapping nano‐architectures enable absorption enhancement to exceed the conventional upper limit and have great potential for achieving state‐of‐the art optoelectronic performances. However, it remains a great challenge to design and fabricate a superior hierarchical light‐trapping nano‐architecture, which exhibits extraordinary light‐harvesting ability and simultaneously avoids deteriorating the electrical performance of PSCs. Herein, colorful efficient moiré‐PSCs are designed and fabricated incorporating moiré interference structures by the imprinting method with the aid of a commercial DVD disc. It is experimentally and theoretically demonstrated that the light harvesting ability of the moiré interference structure can be well manipulated through changing the rotation angle (0°–90°). The boosted short‐circuit current is credited to augment light diffraction channels, leading to elongated optical paths, and fold sunlight into the perovskite layer. Moreover, the imprinting process suppresses the trap sites and voids at the active‐layer interfaces with eliminated hysteresis. The moiré‐PSC with an optimized 30° rotation angle achieves the best enhancement of light harvesting (28.5% higher than the pristine), resulting in efficiencies over 20.17% (MAPbI₃) and 21.76% ((FAPbI₃)_{1‐ x} (MAPbBr₃) _x ).

Perovskite Solar Cells In their Communication on page 6294, Jing Cao et al. report the preparation of a nickel phthalocyanine decorated with four methoxyethoxy units and its application as a hole‐transporting material in perovskite solar cells.

A simple boric acid assisted strategy is used to tailor the morphology and optoelectronic properties of NiO _x with a solar cell efficiency over 21%, a high open‐voltage of 1.131 V, and a high fill factor of 80.9%. Enhanced hole extraction and transport are responsible for the high performance inverted planar methylammonium lead iodide photovoltaic devices.

Metal halide perovskite solar cells (PSCs) have emerged as one of the most promising photovoltaic technologies. For inverted planar PSCs, nickel oxide (NiO _x ) layers, as inorganic p‐type semiconductors, are competitive hole transport layers (HTLs) because of their low cost, chemical stability, and easy preparation. However, their inferior device performance still lags behind the devices using organic HTLs. Herein, a boric acid‐assisted strategy for NiO _x HTLs is reported that enables compact film deposition and electronic modulation. Boron doping can enhance conductivity and deepen the valence band edge, leading to efficient hole extraction and transport. A methylammonium lead iodide (MAPbI₃) photovoltaic device based on our strategy achieves an optimized efficiency of 21.40% with a high open voltage of 1.131 V and a high fill factor of 80.9% with negligible hysteresis, as well as excellent stability.

Herein, a new and dopant‐free polymeric hole‐transporting layer, i.e., poly{2,7‐[(5,5‐bis(3′,7′‐dimethyloctyl)‐5 H‐1,8‐dithia‐as‐indacenone]‐alt‐5,5‐[5′,6′‐bis(octyloxy)‐4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole]} (PDTIDTBT), for mesoscopic perovskite solar cells is synthesized and the efficiency and stability of the cells are improved as compared with spiro‐based devices.

Addressing the stability issue in perovskite solar cells (PSCs) is a crucial step for commercialization purposes. Finding a novel and stable hole‐transporting layer (HTL) is one of the most effective strategies to solve this problem. Herein, a new polymeric HTL, namely poly{2,7‐[(5,5‐bis(3′,7′‐dimethyloctyl)‐5 H‐1,8‐dithia‐as‐indacenone]‐alt‐5,5‐[5′,6′‐bis(octyloxy)‐4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole]} (PDTIDTBT) is synthesized, indicating a great hole‐transporting property as compared with the commonly used 2,2′,7,7′‐tetrakis[N,N‐di(4‐methoxyphenyl)amino]‐9,9′‐spirobifluorene (spiro‐OMeTAD) HTL. This polymer shows good mobility with suitable band alignment with respect to the triple A‐cation perovskite film, which is comparable with the state‐of‐art polymeric HTLs. Therefore, mesoscopic PSCs are fabricated by PDTIDTBT HTL and considered interface engineering technique using a thin layer of poly(methyl methacrylate) (PMMA) at the perovskite/HTL interface. Based on these modifications, a PSC with a maximum power conversion efficiency (PCE) of 19.89% is achieved, higher than the PCE of the spiro‐based PSC (19.28%). In addition, the PDTIDTBT‐based PSCs show excellent operational and ambient stability better than the spiro ones.

The application of additive engineering in tin perovskite solar cells is reviewed, from the aspects of the structures and properties of tin perovskite, additives used for stabilizing divalent Sn²⁺, purifying the tin source to improving the crystalline quality. In addition, challenges and perspectives are proposed to promote the performance of tin perovskite solar cells.

Perovskite solar cells (PSCs) have emerged as one of the third-generation photovoltaic technologies. However, the toxicity issue of the lead element in perovskite absorbers hinders their large-scale production. Thus, exploiting lead-free perovskite materials becomes an important solution to overcome this challenge. Among all the candidates, tin perovskites have advanced rapidly in recent years due to their low toxicity, favorable bandgap, and high carrier mobility. After a few years of development, the highest power conversion efficiency (PCE) of tin PSCs has exceeded 13%, which is mainly attributed to the breakthroughs arising from additive engineering of the Sn perovskite layer. Herein, the role of additive engineering in the research community of tin PSCs is emphasized. First, the crystal structure, electronic characteristics, and the chemical instability of Sn perovskites are introduced. Next, additives used for stabilizing the Sn²⁺ components, purifying SnI₂ sources, and improving the crystal quality of perovskite films are discussed in detail. Finally, challenges and perspectives are laid out to advance the properties of tin halide perovskites for further improving the device efficiency and stability.

Notable developments of SnO₂ as an electron‐selective layer for efficient perovskite solar cells (PSCs) are reviewed, along with an overview of the fabrication methods and interfacial passivation routes. Furthermore, techno‐economic and toxicology analyses of SnO₂ are discussed for possible large‐scale deployment of PSCs. Finally, the role of SnO₂ in scaled module and tandem solar cell production is revealed.

Abstract

Perovskite solar cells (PSCs) have become a promising photovoltaic (PV) technology, where the evolution of the electron‐selective layers (ESLs), an integral part of any PV device, has played a distinctive role to their progress. To date, the mesoporous titanium dioxide (TiO₂)/compact TiO₂ stack has been among the most used ESLs in state‐of‐the‐art PSCs. However, this material requires high‐temperature sintering and may induce hysteresis under operational conditions, raising concerns about its use toward commercialization. Recently, tin oxide (SnO₂) has emerged as an attractive alternative ESL, thanks to its wide bandgap, high optical transmission, high carrier mobility, suitable band alignment with perovskites, and decent chemical stability. Additionally, its low‐temperature processability enables compatibility with temperature‐sensitive substrates, and thus flexible devices and tandem solar cells. Here, the notable developments of SnO₂ as a perovskite‐relevant ESL are reviewed with emphasis placed on the various fabrication methods and interfacial passivation routes toward champion solar cells with high stability. Further, a techno‐economic analysis of SnO₂ materials for large‐scale deployment, together with a processing‐toxicology assessment, is presented. Finally, a perspective on how SnO₂ materials can be instrumental in successful large‐scale module and perovskite‐based tandem solar cell manufacturing is provided.

Publication date: June 2021

Source: Nano Energy, Volume 84

Author(s): Dong Yang, Xiaorong Zhang, Yuchen Hou, Kai Wang, Tao Ye, Jungjin Yoon, Congcong Wu, Mohan Sanghadasa, Shengzhong (Frank) Liu, Shashank Priya

A simple, solution-processed, highly transparent, and cost-effective polyelectrolyte hole transport layer (HTL) consisting of copper (II) poly(styrene sulfonate) (Cu:PSS) is introduced and employed in inverted perovskite solar cells. Easily reduced Cu²⁺ counter-ions balance the negative charges on the PSS polyelectrolyte backbone, supporting p-doping at the interface with the perovskite and Cu:PSS and allowing efficient extraction of p-type carriers at the anode.

Abstract

One effective strategy to improve the performance of perovskite solar cells (PSCs) is to develop new hole transport layers (HTLs). In this work, a simple polyelectrolyte HTL, copper (II) poly(styrene sulfonate) (Cu:PSS), which comprises easily reduced Cu²⁺ counter-ions with an anionic PSS polyelectrolyte backbone is investigated. Photoelectron spectroscopy reveals an increase in the work function of the anode and upward band bending effect upon incorporation of Cu:PSS in PSC devices. Cu:PSS shows a synergistic effect when mixed with polyethylenedioxythiophene: polystyrenesulfonate (PEDOT:PSS) in various proportions and results in a decrease in the acidity of PEDOT:PSS as well as reduced hysteresis in completed devices. Cu:PSS functions effectively as a HTL in PSCs, with device parameters comparable to PEDOT:PSS, while mixtures of Cu:PSS with PEDOT:PSS shows greatly improved performance compared to PEDOT:PSS alone. Optimized devices incorporating Cu:PSS/PEDOT:PSS mixtures show an improvement in efficiency from 14.35 to 19.44% using a simple CH₃NH₃PbI₃ active layer in an inverted (P-I-N) geometry, which is one of the highest values yet reported for this type of device. It is expected that this type of HTL can be employed to create p-type contacts and improve performance in other types of semiconducting devices as well.

Core/shell metal halide perovskite nanocrystals show enhanced stability and optical properties, which are beneficial for their applications in lighting and displays, solar cells, photodetectors, lasing, photocatalysis, and biomedical imaging. In this review, recent advances in synthetic strategies and shell growth of core/shell nanocrystals are reviewed, and their enhanced material properties and emerging applications are discussed.

Abstract

Core/shell structured metal halide perovskite nanocrystals (NCs) are emerging as a type of material with remarkable optical and electronic properties. Research into this field has been developing and expanding rapidly in recent years, with significant advances in the studies of the shell growth mechanism and in understanding of properties of these materials. Significant enhancement of both the stability and the optical performance of core/shell perovskite NCs are of particular importance for their applications in optoelectronic technologies. In this review, the recent advances in core/shell structured perovskite NCs are summarized. The band structures and configurations of core/shell perovskite NCs are elaborated, the shell classification and shell engineering approaches, such as perovskites and their derivative shells, semiconductor shell, oxide shell, polymer shell, etc. are reviewed, and the shell growth mechanisms are discussed. The prospective of these NCs in lighting and displays, solar cells, photodetectors, and other devices is discussed in the light of current knowledge, remaining challenges, and future opportunities.