liuxinye

This work mainly focuses on materials composition and working mechanism of the hydroiodic acid (HI) hydrolysis‐derived intermediate compound DMAI/DMAPbI _x . Importantly, the main component of the CsPbI₃ film prepared by such precursor is proved to be still inorganic. Finally, the optimized CsPbI₃ film–based device shows significantly enhanced stability in ambient environment with a high power conversion efficiency of 17.32%.

Abstract

Introducing hydroiodic acid (HI) as a hydrolysis‐derived precursor of the intermediate compounds has become an increasingly important issue for fabricating high quality and stable CsPbI₃ perovskite solar cells (PSCs). However, the materials composition of the intermediate compounds and their effects on the device performance remain unclear. Here, a series of high‐quality intermediate compounds are prepared and it is shown that they consist of DMAI/DMAPbI _x . Further characterization of the products show that the main component of this system is still CsPbI₃. Most of the dimethylammonium (DMA⁺) organic component is lost during annealing. Only an ultrasmall amount of DMA⁺ is doped into the CsPbI₃ and its structure is stabilized. Meanwhile, excessive DMA⁺ forms Lewis acid–base adducts and interactions with Pb²⁺ on the CsPbI₃ surface. This process passivates the CsPbI₃ film and decreases the recombination rate. Finally, CsPbI₃ film is fabricated with high crystalline, uniform morphology, and excellent stability. Its corresponding PSC exhibits stable property and improved power conversion efficiency (PCE) up to 17.3%.

A strategy is demonstrated for efficacious regulation of perovskite crystallinity using glycolic acid (GA) against nonvolatile thioglycolic acid (TGA) following dimethyl sulfoxide sublimation, resulting in enhanced device performance. A champion power conversion efficiency as high as 21.32% is achieved for the GA‐based device, which is almost 13% or 20% higher than those of the control device or TGA‐based device.

Abstract

A strategy for efficaciously regulating perovskite crystallinity is proposed by using a volatile solid glycolic acid (HOCH₂COOH, GA) in an FA_0.85MA_0.15PbI₃ (FA: HC(NH₂)₂; MA: CH₃NH₃) perovskite precursor solution that is different from the common additive approach. Accompanied with the first dimethyl sulfoxide sublimation process, the subsequent sublimation of GA before 150 °C in the FA_0.85MA_0.15PbI₃ perovskite film can artfully regulate the perovskite crystallinity without any residual after annealing. The improved film formation upon GA modification induced by the strong interaction between GA and Pb²⁺ delivers a champion power conversion efficiency (PCE) as high as 21.32%. In order to investigate the role of volatility in perovskite solar cells (PSCs), nonvolatile thioglycolic acid (HSCH₂COOH, TGA) with a similar structure to GA is utilized as an additive reference. Large perovskite grains are obtained by TGA modification but with obvious pinholes, which directly leads to an increased defect density accompanied by a decline in PCE. Encouragingly, the champion PCE achieved for GA‐based PSC device (21.32%) is almost 13% or 20% higher than those of the control device or TGA‐based device. In addition, GA‐modified PSCs exhibit the best stability in light‐, thermal‐, and humidity‐based tests due to the improved film formation.

Tin fluoride and methylammonium iodide are employed as precursors for the fabrication of methylammonium tin iodide (MASnI₃) film via an ion exchange/insertion reactions approach, and a highly uniform, pinhole‐free perovskite film is obtained with a high concentration of SnF₂ and a low content of Sn⁴⁺. The corresponding solar cell exhibits the highest power conversion efficiency of 7.78% with high reproducibility and stability.

Abstract

The low toxicity, narrow bandgaps, and high charge‐carrier mobilities make tin perovskites the most promising light absorbers for low‐cost perovskite solar cells (PSCs). However, the development of the Sn‐based PSCs is seriously hampered by the critical issues of poor stability and low power conversion efficiency (PCE) due to the facile oxidation of Sn²⁺ to Sn⁴⁺ and poor film formability of the perovskite films. Herein, a synthetic strategy is developed for the fabrication of methylammonium tin iodide (MASnI₃) film via ion exchange/insertion reactions between solid‐state SnF₂ and gaseous methylammonium iodide. In this way, the nucleation and crystallization of MASnI₃ can be well controlled, and a highly uniform pinhole‐free MASnI₃ perovskite film is obtained. More importantly, the detrimental oxidation can be effectively suppressed in the resulting MASnI₃ film due to the presence of a large amount of remaining SnF₂. This high‐quality perovskite film enables the realization of a PCE of 7.78%, which is among the highest values reported for the MASnI₃‐based solar cells. Moreover, the MASnI₃ solar cells exhibit high reproducibility and good stability. This method provides new opportunities for the fabrication of low‐cost and lead‐free tin‐based halide perovskite solar cells.

We report the profiling of spatial and energetic distributions of trap states in metal halide perovskite single-crystalline and polycrystalline solar cells. The trap densities in single crystals varied by five orders of magnitude, with a lowest value of 2 x 10¹¹ per cubic centimeter and most of the deep traps located at crystal surfaces. The charge trap densities of all depths of the interfaces of the polycrystalline films were one to two orders of magnitude greater than that of the film interior, and the trap density at the film interior was still two to three orders of magnitude greater than that in high-quality single crystals. Suprisingly, after surface passivation, most deep traps were detected near the interface of perovskites and hole transport layers, where a large density of nanocrystals were embedded, limiting the efficiency of solar cells.

Acetic acid (Ac) is used as an antisolvent for preparing perovskite films with excellent optoelectronic properties. Ac is found to not only reduce perovskite film roughness and residual PbI₂ but also generate a passivation effect from the electron‐rich carbonyl group. The best 0.159 cm² devices produce efficiencies of 22.0% for Cs_0.05FA_0.80MA_0.15Pb(I_0.85Br_0.15)₃ and 23.0% for Cs_0.05FA_0.90MA_0.05Pb(I_0.95Br_0.05)₃.

Abstract

Improving the quality of perovskite poly‐crystalline film is essential for the performance of associated solar cells approaching their theoretical limit efficiency. Pinholes, unwanted defects, and nonperovskite phase can be easily generated during film formation, hampering device performance and stability. Here, a simple method is introduced to prepare perovskite film with excellent optoelectronic property by using acetic acid (Ac) as an antisolvent to control perovskite crystallization. Results from a variety of characterizations suggest that the small amount of Ac not only reduces the perovskite film roughness and residual PbI₂ but also generates a passivation effect from the electron‐rich carbonyl group (CO) in Ac. The best devices produce a PCE of 22.0% for Cs_0.05FA_0.80MA_0.15Pb(I_0.85Br_0.15)₃ and 23.0% for Cs_0.05FA_0.90MA_0.05Pb(I_0.95Br_0.05)₃ on 0.159 cm² with negligible hysteresis. This further improves device stability producing a cell that maintained 96% of its initial efficiency after 2400 h storage in ambient environment (with controlled relative humidity (RH) <30%) without any encapsulation.

A stable intermediate‐state film is obtained by using teramethylene sulfoxide (TMSO), originating from the formation of stronger coordination bond between TMSO and all perovskite precursors, which extends the annealing window and promotes the formation of a high‐quality film with larger grains and textured surface. 21.14% efficiency is achieved attributable to the improvement of the long‐wavelength response and fill factor.

Abstract

As the power conversion efficiency (PCE) of perovskite solar cells (PSCs) is increased to as high over 25%, it becomes pre‐eminent to study a scalable process with wide processing window to fabricate large‐area uniform perovskite films with good light‐trapping performance. A stable and uniform intermediate‐state complex film is obtained by using tetramethylene sulfoxide (TMSO), which extends the annealing window to as long as 20 min, promotes the formation of a high‐quality perovskite film with larger grains (over 400 nm) and spontaneously forms the surface texture to result in an improved fill factor and open‐circuit voltage (V _oc). Moreover, the superior surface texture significantly increases the long‐wavelength response, leading to an improved short‐circuit current density (J _sc). As a result, the maximum PCE of 21.14% is achieved based on a simple planar cell structure without any interface passivation. Moreover, a large area module with active area of 6.75 cm² is assembled using the optimized TMSO process, showing efficiency as high as 16.57%. The study paves the way to the rational design of highly efficient PSCs for potential scaled‐up production.

A polar nonconjugated small molecule ultrathin layer with an intrinsic dipole moment is introduced to modify the work function of indium tin oxide and to optimize the front interface energy level alignment, which contributes to suppressed energy loss and results in a 20.55% efficient electron transport layer–free perovskite solar cell with enhanced open‐circuit voltage short circuit current density and fill factor, simultaneously.

Abstract

Efficient electron transport layer–free perovskite solar cells (ETL‐free PSCs) with cost‐effective and simplified design can greatly promote the large area flexible application of PSCs. However, the absence of ETL usually leads to the mismatched indium tin oxide (ITO)/perovskite interface energy levels, which limits charge transfer and collection, and results in severe energy loss and poor device performance. To address this, a polar nonconjugated small‐molecule modifier is introduced to lower the work function of ITO and optimize interface energy level alignment by virtue of an inherent dipole, as verified by photoemission spectroscopy and Kelvin probe force microscopy measurements. The resultant barrier‐free ITO/perovskite contact favors efficient charge transfer and suppresses nonradiative recombination, endowing the device with enhanced open circuit voltage, short circuit current density, and fill factor, simultaneously. Accordingly, power conversion efficiency increases greatly from 12.81% to a record breaking 20.55%, comparable to state‐of‐the‐art PSCs with a sophisticated ETL. Also, the stability is enhanced with decreased hysteresis effect due to interface defect passivation and inhibited interface charge accumulation. This work facilitates the further development of highly efficient, flexible, and recyclable ETL‐free PSCs with simplified design and low cost by interface electronic structure engineering through facile electrode modification.

Nanoporous Au film is successfully introduced into perovskite solar cells to replace the typical thermal deposition of metal electrode with a high efficiency of 19.0% on rigid substrate and sustains an excellent bending durability of 98.5% even after 1000 cycles testing on a flexible device, while its facile and recycled utilization significantly reduces the device fabrication cost, noble metal consuming, and environmental pollution.

Abstract

Perovskite solar cells (PSCs) using metal electrodes have been regarded as promising candidates for next‐generation photovoltaic devices because of their high efficiency, low fabrication temperature, and low cost potential. However, the complicated and rigorous thermal deposition process of metal contact electrodes remains a challenging issue for reducing the energy pay‐back period in commercial PSCs, as the ubiquitous one‐time use of a contact electrode wastes limited resources and pollutes the environment. Here, a nanoporous Au film electrode fabricated by a simple dry transfer process is introduced to replace the thermally evaporated Au electrode in PSCs. A high power conversion efficiency (PCE) of 19.0% is demonstrated in PSCs with the nanoporous Au film electrode. Moreover, the electrode is recycled more than 12 times to realize a further reduced fabrication cost of PSCs and noble metal materials consumption and to prevent environmental pollution. When the nanoporous Au electrode is applied to flexible PSCs, a PCE of 17.3% and superior bending durability of ≈98.5% after 1000 cycles of harsh bending tests are achieved. The nanoscale pores and the capability of the porous structure to impede crack generation and propagation enable the nanoporous Au electrode to be recycled and result in excellent bending durability.

The aprotic butyldimethylsulfonium‐driven MAPbI₃ perovskite shows a much more pronounced effect on the improvement of moisture stability compared to the protic butylammonium (BA)‐based counterpart. The BA having a potential hydrogen donor, which exists on the surface and/or grain boundaries, is vulnerable to H₂O‐induced degradation initiators, resulting in the faster hydration followed by the irreversible degradation of perovskites.

Abstract

Many organic cations in halide perovskites have been studied for their application in perovskite solar cells (PSCs). Most organic cations in PSCs are based on the protic nitrogen cores, which are susceptible to deprotonation. Here, a new candidate of fully alkylated sulfonium cation (butyldimethylsulfonium; BDMS) is designed and successfully assembled into PSCs with the aim of increasing humidity stability. The BDMS‐based perovskites retain the structural and optical features of pristine perovskite, which results in the comparable photovoltaic performance. However, the fully alkylated aprotic nature of BDMS shows a much more pronounced effect on the increase in humidity stability, which emphasizes a generic electronic difference between protic ammonium and aprotic sulfonium cation. The current results would pave a new way to explore cations for the development of promising PSCs.

Device model simulation is a macroscopic computer‐assisted tool for modeling organic and organic–inorganic hybrid perovskite solar cells. It simulates the underlying physical mechanisms of the electrical characteristics, such as space‐charge‐limited current, injection‐limited current, ohmic contact, short‐circuit current density, open‐circuit voltage, J–V hysteresis phenomena, power conversion efficiency in the present of surface recombination, trap/defect dependent recombination, or direct band recombination.

Abstract

Device model simulation is one of the primary tools for modeling thin film solar cells from organic materials to organic–inorganic perovskite materials. By directly connecting the current density–voltage (J–V) curves to the underlying device physics, it is helpful in revealing the working mechanism of the heatedly discussed organic–inorganic hybrid perovskite solar cells. Some distinctive optoelectronic features need more phenomenological models and accurate simulations. Herein, the application of the device model method in the simulation of organic and organic–inorganic perovskite solar cells is reviewed. To this end, the ways of the device model are elucidated by discussing the metal–insulator–metal picture and the equations describing the physics. Next, the simulations on J–V curves of organic solar cells are given in the presence of the space charge, interface, charge injection, traps, or exciton. In the perovskite section, the effects of trap states, direct band recombination, surface recombination, and ion migration on the device performance are systematically discussed from the perspective of the device model simulation. Suggestions for designing perovskite devices with better performance are also given.

In general, mixed cations and anions containing formamidinium (FA), methylammonium (MA), caesium, iodine, and bromine ions are used to stabilize the black α-phase of the FA-based lead triiodide (FAPbI₃) in perovskite solar cells. However, additives such as MA, caesium, and bromine widen its bandgap and reduce the thermal stability. We stabilized the α-FAPbI₃ phase by doping with methylenediammonium dichloride (MDACl₂) and achieved a certified short-circuit current density of between 26.1 and 26.7 milliamperes per square centimeter. With certified power conversion efficiencies (PCEs) of 23.7%, more than 90% of the initial efficiency was maintained after 600 hours of operation with maximum power point tracking under full sunlight illumination in ambient conditions including ultraviolet light. Unencapsulated devices retained more than 90% of their initial PCE even after annealing for 20 hours at 150°C in air and exhibited superior thermal and humidity stability over a control device in which FAPbI₃ was stabilized by MAPbBr₃.

An all‐inorganic mixed‐halide perovskite solar cell with a power conversion efficiency of 16.42% is realized by using a Cs₂CO₃‐doped ZnO electron transport layer, which ascribes to the interfacial energy level tuning for reducing ohmic loss at the contact and enlarging the built‐in potential. A high thermostability is simultaneously obtained via surface defect passivation for improving the CsPbI₂Br film against phase transformation.

Abstract

Inorganic mixed‐halide CsPbX₃‐based perovskite solar cells (PeSCs) are emerging as one of the most promising types of PeSCs on account of their thermostability compared to organic–inorganic hybrid counterparts. However, dissatisfactory device performance and high processing temperature impede their development for viable applications. Herein, a facile route is presented for tuning the energy levels and electrical properties of sol–gel‐derived ZnO electron transport material (ETM) via the doping of a classical alkali metal carbonate Cs₂CO₃. Compared to bare ZnO, Cs₂CO₃‐doped ZnO possesses more favorable interface energetics in contact with the CsPbI₂Br perovskite layer, which can reduce the ohmic loss to a negligible level. The optimized PeSCs achieve an improved open‐circuit voltage of 1.28 V, together with an increase in fill factor and short‐circuit current. The optimized power conversion efficiencies of 16.42% and 14.82% are realized on rigid glass substrate and flexible plastic substrate, respectively. A high thermostability can be simultaneously obtained via defect passivation at the Cs₂CO₃‐doped ZnO/CsPbI₂Br interface, and 81% of the initial efficiency is retained after aging for 200 h at 85 °C.