Progress and Challenges Toward Effective Flexible Perovskite Solar Cells

The demand for building-integrated photovoltaics and portable energy systems based on flexible photovoltaic technology such as perovskite embedded with exceptional flexibility and a superior power-to-mass ratio is enormous.The photoactive layer,i.e.,the perovskite thin film,as a critical component of flexible perovskite solar cells(F-PSCs),still faces long-term stability issues when deformation occurs due to encountering temperature changes that also affect intrinsic rigidity.This literature investigation summarizes the main factors responsible for the rapid destruction of F-PSCs.We focus on long-term mechanical stability of F-PSCs together with the recent research protocols for improving this performance.Furthermore,we specify the progress in F-PSCs concerning precise design strategies of the functional layer to enhance the flexural endurance of perovskite films,such as internal stress engineering,grain boundary modification,self-healing strategy,and crystallization regulation.The existing challenges of oxygen-moisture stability and advanced encapsulation technologies of F-PSCs are also discussed.As concluding remarks,we propose our viewpoints on the large-scale commercial application of F-PSCs.

Stitching Perovskite Grains with Perhydropoly(Silazane)Anti-Template-Agent for High-Efficiency and Stable Solar Cells Fabricated in Ambient Air

All inorganic CsPbI_(3)perovskite solar cells(PSCs)have emerged as disruptive photovoltaic technology owing to their admirable photoelectric properties and the non-volatile active layer.However,the phase instability against moisture severely limits the fabrication environment for the high-efficiency devices,breaking through the confinement region to achieve scalable manufacturing has been the primary issue for future commercialization.Here,we develop a curing-anti-solvent strategy for fabricating high-quality and stable black-phase CsPbI_(3)perovskite films in ambient air by introducing an inorganic polymer perhydropolysilazane(PHPS)into methyl acetate to form anti-template agent.The cross-linked PHPS reduces moisture erosions while the hydrolyzate silanol network(–Si(OH)_(4)^(–))controls the perovskite crystal growth by forming Lewis adducts with PbI_(2)during the fabrication.The polycondensation adduct of Si–O–Si/Si–O–Pb strongly binds to CsPbI_(3)grains as a shield layer to hamper phase transition.Using the inorganic CsPbI_(3)perovskite thin-film with PHPS-modified anti-solvent processing as the light absorber,the n–i–p planar solar cell achieved an efficiency of 19.17%under standard illumination test conditions.More importantly,the devices showed excellent moisture stability,retaining about 90%of the initial efficiency after 1000 h under 30%RH.

A New Method for Fitting Current–Voltage Curves of Planar Heterojunction Perovskite Solar Cells

Herein we propose a new equivalent circuit including double heterojunctions in series to simulate the current–voltage characteristic of P–I–N planar structure perovskite solar cells. This new method can theoretically solve the dilemma of the parameter diode ideal factor being larger than2 from an ideal single heterojunction equivalent circuit,which usually is in the range from 1 to 2. The diode ideal factor reflects PN junction quality, which influences the recombination at electron transport layer/perovskite and perovskite/hole transport layer interface. Based on the double PN junction equivalent circuit, we can also simulate the dark current–voltage curve for analyzing recombination current(Shockley–Read–Hall recombination) and diffusion current(including direct recombination), and thus carrier recombination and transportation characteristics. This new model offers an efficacious and simple method to investigate interfaces condition, film quality of perovskite absorbing layer and performance of transport layer, helping us furtherimprove the device efficiency and analyze the working mechanism.

Novel donor-acceptor-donor structured small molecular hole transporting materials for planar perovskite solar cells

Novel donor-acceptor-donor structured small molecular hole transporting materials are developed through a facile route by crosslinking dithienopyrrolobenzothiadiazole and phenothiazine or triarylamine-based donor units. The strong push/pull electron capability of dithienopyrrolobenzothiadiazole/ phenothiazine and large π-conjugated dithienopyrrolobenzothiadiazole facilitate hole mobility and high conductivity. The devices using the dithienopyrrolobenzothiadiazole/phenothiazine-based hole trans-porting material achieved a power conversion efficiency of 14.2% under 1 sun illumination and improved stability under 20% relative humidity at room temperature without encapsulation. The present finding highlights the potential of dithienopyrrolobenzothiadiazole-based donor-acceptor-donor small molecular hole transporting materials for perovskite solar cells.

Diketopyrrolopyrrole based D-π-A-π-D type small organic molecules as hole transporting materials for perovskite solar cells

Three novel diketopyrrolopyrrole （DPP） based small organic molecules were synthesized as hole transporting materials for perovskite solar cells. The effects of different donors and zr bridges on the performance of perovskite solar cells （PSCs） were discussed. The efficiency of TPADPP-1, TPADPP-2. PTZDPP-2 was 5.10%, 9.85% and 8.16% respectively. Compared to TPADPP-2, the voltage of PTZDPP-2 was higher. Because the electron-donatingability of phenothiazine based donor was larger than that of triphenylamine based donor, the HOMO level of PTZDPP-2 was lower than that of TPADPP-2. The results indicated that the diketopyrrolopyrrole based D-π-A-π-D type small organic molecule might be a promising hole trans- porting material in the perovskite solar cells.

Preventing inhomogeneous elemental distribution and phase segregation in mixed Pb-Sn inorganic perovskites via incorporating PbS quantum dots

Inhomogeneous Pb/Sn elemental distribution and the resulted phase segregation in mixed Pb-Sn halide perovskites would result in energy disorder(band structure and phase distribution disorder),which greatly limits their photovoltaic performance.Here,Pb S quantum dot has been synthesized and demonstrated as seeds for modulation crystallization dynamics of the mixed Pb-Sn inorganic perovskites,allowing an enhanced film quality and significantly suppressing phase segregation.With this additive power conversion efficiency of 8%and 6%is obtained under irradiation of full sunlight in planar and mesoporous structured solar cells in combination with CsPb_(0.5) Sn_(0.5)I_(2)Br inorganic perovskite,respectively.Our finding reveals exploring the actual Pb/Sn atoms location in perovskite structure and its influence on developing efficient and stable low-bandgap perovskite solar cells.

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 pho- tovoltaic parameters of CH3NH3Pbl3-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 CH3NH3PbI3, 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 16Z 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.

Improvement of Cyclic Stability of Na_(0.67)Mn_(0.8)Ni_(0.1)Co_(0.1)O_(2 )via Suppressing Lattice Variation

Strategies to prolong operational life are highly pursued to strengthen the advantage of cost-effectiveness on sodium-ion batteries(SIBs).We demonstrate the crucial influence of particles'internal mechanical strains on durability of cathode,which does not attract enough attentions from the community.Among the investigated samples,2%Ti-modified-Na_(0.67)Ni_(0.1)Co_(0.1)Mn_(0.8)O_(2 )suppresses the c-axis lattice variation by 38%,attains the reversible capacity 86%higher after 200 cycles,and still keeps intact morphology.This approach indicates that the mechanical properties could tailor cyclic stability of cathode,which is particular important to further improve competitiveness for SIBs.

CsPb(I_(x)Br_(1-x))_(3) solar cells

Owing to its nice performance, low cost, and simple solution-processing, organic-inorganic hybrid perovskite solar cell(PSC) becomes a promising candidate for next-generation high-efficiency solar cells.The power conversion efficiency(PCE) has boosted from 3.8% to 25.2% over the past ten years. Despite the rapid progress in PCE, the device stability is a key issue that impedes the commercialization of PSCs. Recently, all-inorganic cesium lead halide perovskites have attracted much attention due to their better stability compared with their organic-inorganic counterpart. In this progress report, we summarize the properties of CsPb(IxBr1-x)3 and their applications in solar cells. The current challenges and corresponding solutions are discussed. Finally, we share our perspectives on CsPb(IxBr1-x)3 solar cells and outline possible directions to further improve the device performance.

Interface engineering gifts CsPbI2.25Br0.75 solar cells high performance

Organic-inorganic halide perovskite (ABX3) solar cells (PSCs)have made great progress in recent years [1]. The power conversion efficiency (PCE) has increased up to 25.2%(NREL Best Research-Cell Efficiency Chart, https://www.nrel.gov/pv/cell-efficiency.html, Accessed August 2019). However, they suffer from poor thermal stability due to the volatile A-site organic cations.

Exploring stability of formamidinium lead trihalide for solar cell application

Formamidinium lead triiodide （FAPbI3） is a promising photoactive perovskite for low-cost and efficient solar cells. This article reports on an experimental investigation on the stability of FAPbI3 by comparison with that of widely-used methylamidinium lead triiodide （MAPbI3）. A hydration of the FAPbI3 with mois- ture could be the dominant mechanism for its degradation in air, rather than a common thermal decom- position in the MAPbI3. This can be mainly contributed to a relatively strong bond formation between formamidinium ions （FA＋） and 1-. Consequently, the stability of FAPbl3 based devices can be greatly enhanced by removal moisture in the surrounding. This conclusion renders FAPbI3 extremely attractive for stable perovskite solar cells with fine encapsulation.

Sn/Pb binary metal inorganic perovskite:a true material worthy of trust for efficient and stable photovoltaic application

The growing global demand for energy makes it essential to develop alternatives to fossil fuels with the aim to solve the issue of the upcoming energy supply shortage and the effect of climate change.Renewable energies with the featuring of inexhaustible natural source are the key for the modern industry’s future in which solar energy in particular is one of the most promising segments.

Photocurrent hysteresis related to ion motion in metal-organic perovskites

Perovskite solar cells have attracted considerable attention in the photovoltaic field for their high efficiency achieved in a short period of time.However,hystersis behaviour was often observed during the photocurrent-voltage measurement causes uncertainty in evaluation of photovoltaic efficiency.In this letter,we report a systematic investigation on the cause of hysteresis via series of TiO_2 based planar heterojunction structured perovskite solar cell devices.The results reveal organic cation ions,such as the commonly employed CH_3NH_3^+ or HC(NH_2)_2^+,play critical role on the observed hysteresis effect above the 298 K via interaction with iodide.We further suggest an efficient hole/electron transport in devices can inhibit such hysteresis behavior.Our conclusion sheds light onto the underlying hysteresis mechanisms,and proposes possible solutions to overcome the issue,which offers guidelines for future development of perovskite devices.

Efficient and Stable Large-Area Perovskite Solar Cells with Inorganic Perovskite/Carbon Quantum Dot-Graded Heterojunction

This work reports on a compositionally graded heterojunction for photovoltaic application by cooperating fluorine-doped carbon quantum dots(FCQDs in short)into the CsPbI_(2.5)Br_(0.5)inorganic perovskite layer.Using this CsPbI_(2.5)Br_(0.5)/FCQDs graded heterojunction in conjunction with low-temperature-processed carbon electrode,a power conversion efficiency of 13.53%for 1 cm^(2)all-inorganic perovskite solar cell can be achieved at AM 1.5G solar irradiation.To the best of our knowledge,this is one of the highest efficiency reported for carbon electrode based all-inorganic perovskite solar cells so far,and the first report of 1 cm^(2)carbon counter electrode based inorganic perovskite solar cell with PCE exceeding 13%.Moreover,the inorganic perovskite/carbon quantum dot graded heterojunction photovoltaics maintained over 90%of their initial efficiency after thermal aging at 85°for 1056 hours.This conception of constructing inorganic perovskite/FCQDs graded heterojunction offers a feasible pathway to develop efficient and stable photovoltaics for scale-up and practical applications.