Enhanced efficiency and stability of perovskite solar cells by 2D perovskite vapor-assisted interface optimization

Organic–inorganic perovskites solar cells(PSCs)have attracted great attention due to their rapid progress in power conversion efficiency(PCE).However,there is still an enormous challenge to achieve both high efficiency and stability devices as the decomposition of perovskite materials under humid and light conditions.Herein,we demonstrate that high efficiency and stability of PSCs can be obtained by the reaction of three-dimensional(3D)perovskite with 1,4-butanediamine iodide(BEAI2)vapor.The incorporation of BEAI2 intensively promotes the crystallization of perovskite film with large grain size(~500 nm).Further characterization reveals that the post-treatment perovskite film delivered low interface trap density with long carrier lifetime(>200 ns),long carrier diffusion length(>600 nm)and large carrier mobility(>1.5 cm^2 V-1S-1).Solar cells employing such post-treatment films demonstrated 19.58%PCE without hysteresis.Moreover,the post-treatment devices can retain over 90%original efficiencies stored under ambient atmospheric conditions and exhibit better stability under 85℃and continuous illumination as a two-dimensional(2D)perovskite thin layer is formed on the surface/or at the grain boundaries of 3D perovskite.This study offers an effective way to obtain PSCs with high efficiency and stability.     

Reductive ionic liquid-mediated crystallization for enhanced photovoltaic performance of Sn-based perovskite solar cells

Tin (Sn)-based perovskite solar cells (PSCs) have recently made inspiring progress,and certified power conversion efficiency(PCE) has reached impressive value of 14.8%.However,it is still challenging to realize efficient and stable 3D Sn-based PSCs due to the fast crystallization and easy Sn²⁺oxidation of Sn-based perovskite.Herein,we reported the utilization of a reductive ionic liquid,methylamine formate (MAFa),to drive the controlled crystallization process and suppress Sn²⁺     

Development of formamidinium lead iodide-based perovskite solar cells: efficiency and stability

Perovskite materials have been particularly eye-catching by virtue of their excellent properties such as high light absorption coefficient, long carrier lifetime, low exciton binding energy and ambipolar transmission (perovskites have the characteristics of transporting both electrons and holes). Limited by the wider band gap (1.55 eV), worse thermal stability and more defect states, the first widely used methylammonium lead iodide has been gradually replaced by formamidinium lead iodide (FAPbI₃) with a narrower band gap of 1.48 eV and better thermal stability. However, FAPbI₃ is stabilized as the yellow non-perovskite active phase at low temperatures, and the required black phase (α-FAPbI₃) can only be obtained at high temperatures. In this perspective, we summarize the current efforts to stabilize α-FAPbI₃, and propose that pure α-FAPbI₃ is an ideal material for single-junction cells, and a triple-layer mesoporous architecture could help to stabilize pure α-FAPbI₃. Furthermore, reducing the band gap and using tandem solar cells may ulteriorly approach the Shockley–Queisser limit efficiency. We also make a prospect that the enhancement of industrial applications as well as the lifetime of devices may help achieve commercialization of PSCs in the future.

This perspective is focused on the current development state and the future development direction of FA-based perovskite materials and solar cells.     

Review on engineering two-dimensional nanomaterials for promoting efficiency and stability of perovskite solar cells

Perovskite solar cell(PSC) has gradually shown its great superiority in photovoltaic filed to compete commercial solar cells owing to its great advantages, such as high efficiency and low fabrication cost. On the way towards commercialization, great efforts have been achieved by accelerating charge extraction and reducing carrier recombination. Recently, two-dimensional(2 D) layered materials have attracted increasing interests for application in PSCs due to their distinctive chemical and physic...     

Post-treatment by an ionic tetrabutylammonium hexafluorophosphate for improved efficiency and stability of perovskite solar cells

Interface engineering is an effective way to improve efficiency and long-term stability of perovskite solar cells(PSCs).Herein,an ionic compound tetrabutylammonium hexafluorophosphate(TP6)is adopted to passivate surface defects of the perovskite film.It is found that TP6 effectively reduced the surface defects,especially at the grain boundaries where the defects are abundant.Meanwhile,the exposed long alkyl chains and fluorine atoms in the TP6 enhanced the moisture stability of the perovskite film due to its strong hydrophobicity.In addition,the driving force of charge carrier separation and transport is increased by enlarged built-in potential.Consequently,the power conversion efficiency(PCE)of PSCs is significantly improved from 20.59% to 22.41%by increased open-circuit voltage(V_oc)and fill factor(FF).The unencapsulated device with TP6 treatment exhibits better stability than the control device,and the PCE retains-80%of its initial PCE after 30 days under 15%-25%relative humidity in storage,while the PCE of the control device declines by more than 50%.     

Supersaturation controlled growth of MAFAPbI_3 perovskite film for high efficiency solar cells

Controlling the nucleation and growth of organic-inorganic hybrids perovskite is of key importance to improve the morphology and crystallinity of perovskite films. However, the growth mechanism of perovskite films based on classical crystallization theory is not fully understood. Here, we develop a supersaturation controlled strategy(SCS) to balance the nucleation and crystal growth speeds. By this strategy, we are able to find an ideal supersaturation region to realize a balance of nucleation and crystal growth, which yields highly crystallized perovskite films with micrometer-scale grains. Besides, we provide a thoughtful analysis of nucleation and growth based on the fabrication of the perovskite films. As a result, the highest photovoltaic power conversion efficiencies(PCE) of 19.70% and 20.31% are obtained for the planar and the meso-superstructured devices, respectively. This strategy sheds some light for understanding the film growth mechanism of high quality perovskite film, and it provides a facile strategy to fabricate high efficiency perovskite solar cells.     

Fullerenes with dipoles: boosting the efficiency of perovskite solar cells

An unfortunate and fortunate discovery is that metal halide perovskites are not completely defect tolerant,while fullerenes,which are inexpensive and broadly applied in organic solar cells,have a considerable passivation effect toward the surface defects of perovskite materials[1].The improvement of perovskite efficiency and stability in the last five years has shown the importance of passivating interfacial charge traps to reduce charge carrier recombination and to slow down the degradation of perovskites[2].     

Perovskite tandem solar cells with improved efficiency and stability

Tandem solar cells represent an attractive technology to overcome the Shockley-Queisser limit of single-junction cells.Recently,wide-bandgap metal halide perovs...     

Organic additives in all-inorganic perovskite solar cells and modules:from moisture endurance to enhanced efficiency and operational stability

Power conversion efficiency(PCE) of perovskite solar cells(PSC) has been skyrocketed to certified 25.5% owing to their improved and tunable optoelectronic properties. Although, various strategies have been adopted to date regarding PCE and stability enhancement within PSC technology, certain instability factors(moisture, heat, light) are hindering their commercial placement. Recently, all-inorganic PSCs got hype in the photovoltaic research community after they attained PCE > 20% and due to t...     

Effect of temperature on the efficiency of organometallic perovskite solar cells

In recent years perovskite solar cells have attracted an increasing scientific and technological interest in the scientific community. It is important to know that the temperature is one of the factors which have a strong effect on the efficiency of perovskite solar cell. This study communicates a temperature analysis on the photovoltaic parameters of CH_3NH_3PbI_3-based perovskite solar cell in a broad interval from 80 to 360 K. Strong temperature-dependent photovoltaic effects have been observed in the type of solar cell, which could be mainly attributed to CH_3NH_3PbI_3, showing a ferroelectric-paraelectric phase transition at low temperature(T 160 K). An increase in temperature over the room temperature decreased the perovskite solar cell performance and reduced its efficiency from 16% to 9%. The investigation with electronic impedance spectroscopy reveals that at low temperature(T 120 K) the charge transport layer limits the device performance, while at high temperature(T 200 K), the interfacial charge recombination becomes the dominant factor.     

4-Tert-butylpyridine-assisted low-cost and soluble copper phthalocyanine as dopant-free hole transport layer for efficient Pb- and Sn-based perovskite solar cells

The preparation of suitable hole transport material(HTM) is critical to the performance and stability of perovskite solar cells(PSCs) with low-cost. Herein, a mass producible and soluble copper phthalocyanine decorated with butoxy donor groups(CuPcOBu) was designed as HTM and prepared by a facile two-step synthetic route. To generate high quality HTM film, 4-tertbutylpyridine(tBP) was doped into CuPc-OBu to prepare the film and then removed by annealing. Such a t BP-assisted strategy resulted in the best efficiency of the PSCs with lead trihalide perovskite up to 19.0%(small-area of 0.1 cm~2) and 10.1%(the active area of 8.0 cm~2 for the module device). And the best efficiency of the tin-based PSCs with CuPc-OBu reached to 6.9%.More importantly, the device with CuPc-OBu as HTM revealed the remarkably enhanced stability. This work provides a new strategy to improve the film-quality of free-doping HTMs and enhance the efficiency and stability of Pb-and Sn-based PSCs with low-cost.     

Defect passivation by nontoxic biomaterial yields 21% efficiency perovskite solar cells

Defect passivation is one of the most important strategies to boost both the efficiency and stability of perovskite solar cells(PSCs).Here,nontoxic and sustainable forest-based biomaterial,betulin,is first introduced into perovskites.The experiments and calculations reveal that betulin can effectively passivate the uncoordinated lead ions in perovskites via sharing the lone pair electrons of hydroxyl group,promoting charge transport.As a result,the power conversion efficiencies of the p-i-n planar PSCs remarkably increase from 19.14%to 21.15%,with the improvement of other parameters.The hydrogen bonds of betulin lock methylamine and halogen ions along the grain boundaries and on the film surface and thus suppress ion migration,further stabilizing perovskite crystal structures.These positive effects enable the PSCs to maintain 90%of the initial efficiency after 30 days in ambient air with 60%±5%relative humidity,75%after 300 h aging at 85℃,and 55%after 250 h light soaking,respectively.This work opens a new pathway for using nontoxic and low-cost biomaterials from forest to make highly efficient and stable PSCs.     

Defect mitigation using d-penicillamine for efficient methylammonium-free perovskite solar cells with high operational stability

Trap-dominated non-radiative charge recombination is one of the key factors that limit the performance of perovskite solar cells (PSCs), which was widely studied in methylammonium (MA) containing PSCs. However, there is a need to elucidate the defect chemistry of thermally stable, MA-free, cesium/formamidinium (Cs/FA)-based perovskites. Herein, we show that d-penicillamine (PA), an edible antidote for treating heavy metal ions, not only effectively passivates the iodine vacancies (Pb²⁺ defects) through coordination with the –SH and –COOH groups in PA, but also finely tunes the crystallinity of Cs/FA-based perovskite film. Benefiting from these merits, a reduction of non-radiative recombination and an increase in photoluminescence lifetime have been achieved. As a result, the champion MA-free device exhibits an impressive power conversion efficiency (PCE) of 22.4%, an open-circuit voltage of 1.163 V, a notable fill factor of 82%, and excellent long-term operational stability. Moreover, the defect passivation strategy can be further extended to a mini module (substrate: 4 × 4 cm², active area: 7.2 cm²) as well as a wide-bandgap (∼1.73 eV) Cs/FA perovskite system by delivering PCEs of 16.3% and 20.2%, respectively, demonstrating its universality in defect passivation for efficient PSCs.

Iodine vacancy defects in MA-free perovskite are effectively passivated through the interaction between Pb²⁺ and the functional groups in d-penicillamine, resulting in an impressive efficiency of 22.4% along with excellent operational stability.     

Polymer strategies in perovskite solar cells

Since their emergence in 2013, perovskite solar cells have reached remarkable efficiencies exceeding 22%. Such rapid development of this technology has been possible, in part, due to the feed of ideas from previous research in organic photovoltaics (OPVs) and light emitting diodes (OLEDs). This comprehensive review discusses the various polymer strategies that have led to the success of perovskite devices: from hole and electron transporting materials to polymer templating agents. This review further covers how these strategies potentially serve to overcome the two major obstacles that stand in the way of global implementation of perovskite solar cells; stability and J‐V curve hysteresis. Through reference and comparison of OPV, OLED, and perovskite technologies, we highlight the need for a unified approach to establish appropriate control systems and ageing protocols that are necessary to further research in this exciting direction. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 549–568     

Advances in perovskite quantum-dot solar cells

Perovskite quantum-dots (PQDs) have emerged as prominent candidates for intriguing photovoltaic application due to their superior optoelectronic properties such as multiple exciton generation, bandgap tunability, electronic and surface chemistry properties, as well as flexible composition [1–5].     

Molecular exchange and passivation at interface afford high-performing perovskite solar cells with efficiency over 24%

The interface is crucial for perovskite solar cells(PSCs). However, voids at interfaces induced by the trapped hygroscopic dimethyl sulfoxide(DMSO) can reduce charge extraction and accelerate the film degradation, seriously damaging the efficiency and stability. In this work, 4,4’-dinonyl-2,2’-dipyridine(DN-DP), a Lewis base with long alkyl chains is introduced to solve this problem. Theoretical calculated and experimental results confirm that the dipyridyl group on DN-DP can more strongly coord...     

Stable perovskite solar cells with efficiency of 22.6% via quinoxaline-based polymeric hole transport material

Science China Chemistry - Poor stability of spiro-OMeTAD hole transport materials (HTM) with dopant is a major obstacle for the commercialization of perovskite solar cell (pero-SC). Herein, we...     

Application of an amphipathic molecule at the NiOx/perovskite interface for improving the efficiency and long-term stability of the inverted perovskite solar cells

The presence of defects and detrimental reactions at NiO_x/perovskite interface extremely limit the efficiency performance and long-term stability of the perovskite solar cells(PSCs) based on NiO_x.Herein,an amphipathic molecule Triton X100(Triton) is modified on the NiO_x surface.The hydrophilic chain of Triton as a Lewis base additive can coordinate with the Ni³⁺ on the NiO_x surface which can passivate the interfacial defects and hinder the d...     

Surface-functionalized hole-selective monolayer for high efficiency single-junction wide-bandgap and monolithic tandem perovskite solar cells

Carbazole moiety-based 2PACz([2-(9H-carbazol-9-yl)ethyl]phosphonic acid) self-assembled monolayers(SAMs) are excellent hole-selective contact(HSC) materials with abilities to excel the charge-transferdynamics of perovskite solar cells(PSCs). Herein, we report a facile but powerful method to functionalize the surface of 2PACz-SAM, by which reproducible, highly stable, high-efficiency wide-bandgap PSCs can be obtained. The 2PACz surface treatment with various donor number solvents improves assembl...     

Interfacial modification using the cross-linkable tannic acid for highly-efficient perovskite solar cells with excellent stability

Although the performance of perovskite solar cells(PSCs) has been dramatically increased in recent years,stability is still the main obstacle preventing the PSCs from being commercial. PSC device instability can be caused by a variety of reasons, including ions diffusion, surface and grain boundary defects, etc. In this work, the cross-linkable tannic acid(TA) is introduced to modify perovskite film through post-treatment method. The numerous organic functional groups(–OH and C=O) in TA can inte...