Perovskite: a new material of "net red" solar cell

When it comes to solar cells, materials are indispensable The earliest solar cell with practical value was made of monocrystalline silicon Since its birth in 1950s, the energy conversion efficiency of the single crystal silicon solar cell has reached 25% Despite more than 60 years of research and development efforts, the cost of such batteries is still too high, limiting their large-scale commercial applications At the turn of thousands of years, scientists began to design the latest generation of solar cells, and put forward the basic requirements, including the material should be composed of high abundance elements in the earth's crust, environment-friendly, simple and easy to enlarge technology, high efficiency and low energy consumption So a large number of new solar cells came into being, such as dye-sensitized cells, quantum dot sensitized cells, quantum dot cells, organic solar cells and so on Although these solar cells provide a good research platform, the energy conversion efficiency growth is too slow or even stagnant It is in this context that perovskite solar cells have emerged and attracted worldwide attention It turns out that a kind of organic-inorganic hybrid perovskite material (such as lead halide ch3nh3pbx3, x = Cl, Br, I) has very excellent photoelectric properties during the research of dye-sensitized batteries In 2009, Japanese scientists applied organic-inorganic hybrid perovskite materials to quantum dot sensitized solar cells for the first time, and prepared the first perovskite solar cell, achieving a photoelectric conversion efficiency of 3.8% In the five years from 2009 to 2014, the energy conversion efficiency of solar cells made of this kind of materials as light absorbing layer has jumped from 3.8% to 19.3%, which is more than five times higher The main reason for the success is to replace the liquid electrolyte commonly used in dye-sensitized batteries with a quasi-solid hole transport material layer, so as to improve the stability of the batteries and the photoelectric conversion efficiency Then perovskite solar cells have become a global research hotspot Now the energy conversion efficiency has increased to 22.1%, becoming a "new star" in the field of the third generation solar cells Why is perovskite solar cell so hot in the short term? We have to start with the perovskite material itself Generally speaking, the perovskite material we are talking about can be expressed as ABX3 (a = short chain organic amine ion or alkali metal ion, B = lead, tin, germanium, x = halogen ion) In the structure of ABX3, each a-ion is connected with 12 x-ions, and each B-Ion is connected with 6 x-ions, thus forming a three-dimensional structure of [BX6] octahedron co angle extension Its remarkable advantage is that even with the low-cost solution method, high-quality films with good crystallinity can be formed It is found that this kind of material is a direct band gap semiconductor, which not only has good optical absorption, but also has very excellent equilibrium electron hole transport properties The carrier diffusion length of perovskite film can reach several hundred nanometers, which makes this kind of material no longer limited to porous titanium dioxide structure, but suitable for simple plane structure At a deeper level, these excellent properties come from the special electronic structure and bonding form of materials Interestingly, the particularity of this material makes the defects, even if they exist, only belong to benign defects, thus minimizing the negative impact on the device All in all, the excellent photoelectric properties of perovskite make it have far-reaching and broad device significance, and provide a rare material foundation for the development of a new generation of efficient solar cells Up to now, the basic structures of perovskite solar cells, which are often explored, include n-i-p, p-i-n and carbon based types A typical p-i-n structure is that the calcium titanium ore layer is sandwiched between p-NiO and n-fullerene attached to the conductive transparent glass In recent years, people improve the calcium titanium ore layer, or choose more suitable charge transfer materials, build nanostructures, interfaces and improve the film-forming characteristics, so that the battery can absorb sunlight to the maximum extent, so that the electrodes at both ends can collect more electron holes, so as to obtain a more efficient perovskite solar cell Obviously, the key factor to improve the efficiency of solar cells is to improve the efficiency of photon capture and photocarrier collection The international and domestic counterparts have done a lot of work But limited to space, here is only a brief introduction to a few recently published papers Recently, Professor Han Liyuan's team of Shanghai Jiaotong University published research results on nature, realizing the preparation of large-area high-efficiency perovskite solar cells; hankeli's team of Dalian Institute of Chemical Sciences, Chinese Academy of Sciences, published a paper on J Phys Chem Lett., synthesized a non lead, stable two-dimensional germanium based perovskite material; ACS energy lett., published Yuanyuan, Brown University, USA A prospective review by Professor Zhou and Professor Nitin P padture: formation and transformation of gas-induced organic-inorganic hybrid perovskite materials Han Liyuan's team spent three years to solve the problem that the larger the area of perovskite film, the lower the efficiency of the battery Based on the preparation of large area and high-quality perovskite film, the team developed a perovskite battery module with an effective area of 36.1cm2, which obtained 12.1% certification efficiency for the first time in the international certification body, and established the world record of the efficiency of the first large area perovskite module The appearance of this achievement means that perovskite photovoltaic technology has the possibility of going out of the laboratory and realizing large-scale industrialization in the future The research team used the method of unifying the carbamate with carbamate to make the carbamate molecules in the gas react with the carbamate ions in the perovskite material, and then mixed the products to obtain the liquid of the perovskite material This kind of liquid can quickly release the gas of methylammonium to become perovskite solid, and the released gas of methylammonium can be used again to react with the solid powder of methylammonium iodide and lead iodide to realize the recycling of materials In the film preparation method, the researchers used the one-time forming pressure assisted preparation method By controlling the pressure and coating the liquid material on the flat substrate, the uniformly distributed liquid film was obtained A two-dimensional Ge based perovskite material (PEA) 2gei4 was synthesized by hankley's team The two-dimensional perovskite structure is composed of organic phenylethylamine layer and inorganic germanium iodide layer The layer to layer is connected by van der Waals force, and the layer spacing is 1.65 nm DFT calculation shows that the material is a direct band gap with a band gap value of 2.17 EV, which is consistent with the band gap measured by solid UV absorption, which means that it is suitable for series batteries The two-dimensional Ge based perovskite material can emit fluorescence at room temperature, with a lifetime of more than 1 ns, showing good photovoltaic potential In addition, the stability of perovskite is improved by introducing the two-dimensional layered structure formed by long-chain organic cations This work broadens the research scope of two-dimensional layered perovskite and provides a new idea for the development of non lead perovskite PXRD of magei 3 (a) and (PEA) 2 gei 4 (b) exposed to 60% RH at 25 ℃ An asterisk indicates the signal of gei 4 (source: Professor J Phys Chem Lett.) Zhou and Professor padture have been devoted to the study of the chemical behavior of organic-inorganic hybrid halide perovskite induced by gases, especially amino gases in recent years, with a series of important achievements This review reviews the main work of many research groups in this field, including them, imagines the development direction of this field in the future, and emphasizes the importance of the research of mechanism including theoretical calculation and in-situ characterization The future research contents are as follows: (a) theoretical calculation of the "liquefaction" process of perovskite induced by methylamine; (b) exploration of the existence and importance of nonclassical crystallization mechanism in the process of gas perovskite interaction; (c) prediction reaction mechanism of morphology retained perovskite phase transition under gas induction; (D) different gas perovskite combinations that can be studied in the future (source: ACS energy lett) ）Looking forward to the future, perovskite solar cells have an unlimited future Optimistic, this new star may lead the energy revolution of this century First of all, in the short term, the efficiency of such cells may reach the theoretical limit close to the Shockley queisser limit, that is, the energy conversion efficiency of single junction solar cells Large scale applications may follow, such as flexible solar cells, translucent and color decorated solar cells People may develop rapid and easy to mass production printing technology to realize the production process of roll to roll Perhaps faster is to combine the advantages with the mature technology and the ready-made monocrystalline silicon solar cells of the production device, so as to obtain the high-efficiency and low-cost laminated solar cells There is no denying that opportunities often coexist with challenges At present, the biggest challenge is the urgent need to solve the problem of perovskite stability If not, it may become the "Achilles heel" Especially in humid environment or continuous high temperature and light irradiation, the stability of perovskite is very important Once the stability of perovskite is solved, the life of such solar cells will be greatly extended But the life of perovskite solar cell is very low By contrast, the traditional single crystal silicon solar cells can last up to 25 years In addition, the energy conversion efficiency of perovskite solar cells is further improved through material engineering and device design Finally, we should try to solve the problem of toxicity At present, most of the organic-inorganic hybrid perovskite battery materials in the research contain toxic lead elements, which may cause potential harm to human body and environment Although it is found that tin can replace lead, the energy conversion efficiency of the battery is only 6%, and there is still much room for improvement in the future It should be noted that if effective packaging technology can be adopted, the negative impact of toxicity is expected to be minimized It remains to be seen how long perovskite battery, a new "net red" battery, can be red.