Advanced Energy Materials Laboratory

RESEARCH

Total 1건 1 페이지
Solar cell 목록
번호 제목 작성일
1

Next Generation Solar Cells

Next generation solar cells such as dye-sensitized solar cells (DSSCs), organic solar cell, quantum dot solar cell, and perovskite solar cell have been developed in aspects of ease of fabrication and low-cost. Among them, perovskite solar cells show marked improvement in photovoltaic performances during a short period time since the first demonstration as a solar cell in 2009. In this section, the history and current state on development of perovskite solar cell are briefly introduced.

Perovskite is the name of crystal structure that is discovered inorganic mineral CaTiO3 by Gustave Rose, German mineralogist in 1839 and is named after a Russian mineralogist, Lew A. Perovski. Figure 1 shows a unit cell of cubic ABX3 structure. Materials that have ABX3 specific structure are also known as the perovskite. Each of A, B and X generally represents large rare earth metal cation, small metal cation and anion. A cation is surrounded by 12 X anions due to large atomic size, while the B cation is form the octahedron that is coordinated by 6 X anions due to small atomic size. There are many different perovskites such as CaTiO3, PbTiO3, MgSiO3, SrFeO3, LiNbO3, SrZrO3, BaZrS3, KMgF3, BaTiO3.

Perovskites generally have various different physical properties such as dielectric, ferroelectric, magnetoresistive, thermoelectric, electro-optic, semiconducting, conducting and superconducting, and have been introduced and applied in the divers applications. These physical properties can be depending on the compositions of perovskite structure. An ionic size of perovskite structure affected the distortion of their symmetry changes.

In 1978, organo-inorganic hybrid perovskites (OIHPs) were first reported by Weber, it introduced that A cation can be also replaced by small organic cation such as ethylammonium (CH3CH2NH3+), formamidinium (HC(NH2)2+). In OIHPs, alkyl, aliphatic and aromatic ammonium (R-NH3+) or diammonium (+3HN-R-NH3+) are used as A cations and almost divalent metal cations such as Pb2+, Cd2+, Sn2+ can be used as B cations. And X anions are generally used halides. Functional head group of organic cations interact with inorganic layer and alkyl groups of organic cations are positioned between inorganic sheets. The chemical interaction between ammonium ions and inorganic sheets is very important in the perovskite structure.

Mitzi and coworkers were extensively investigated the fundamental optoelectronic properties of OIHPs due to high charge carrier mobility. Since then, organo-inorganic hybrid perovskites have intensively been studied as a promising light absorber optoelectronic fields including solar cells, light emitting diodes, and lasers because those have superior properties such as high absorption coefficient, small exciton binding energy, long charge carrier diffusion length and high charge carrier mobility, and tunable band gap. Furthermore, organo-inorganic hybrid perovskites are suitable for solution processing because the precursor have enough solubility in several polar aprotic solvents (dimethyl formamide, dimethyl sulfoxide, N-methylpyrrolidone, γ-butyrolactone).

In 2009, Miyasaka’s group applied the CH3NH3PbX3 (X= Br-, I-) compounds as a semiconducting light sensitizer in dye-sensitized solar cell based on I-/I3- liquid electrolyte, exhibiting the promising power conversion efficiency (PCE) of 3.8%. Park’s group improved the performances up to 6.5% by adopting the CH3NH3PbI3 sensitizer, but severe instability of performance still remained in the polar liquid electrolyte. In 2012, there were breakthrough reports showing stable and efficient perovskite solar cells reaching to 10% by substituting the liquid electrolyte with a solid-state hole transport material (2,2'',7,7''-tetrakis(N,N-di-p-methoxyphenylamino)-9,9''-spirobifluorene, spiroOMeTAD). Especially, the perovskite solar cells have shown significant advances within a short span since the first report in 2009 and dramatically reached a high certified PCE of 22.1%. The Figure 2 shows the brief history on development of OIHP and perovskite optoelectronics.

The architectures of perovskite solar cells are commonly used by mesoscopic device according to the presence of mesoporous scaffold layer, the mesoscopic device stems from DSSCs. The compact TiO2 layer plays role in blocking the holes in perovskite layer and preventing a charge recombination. The mesoporous TiO2 layer acts as a scaffold to expand a surface area of perovskite layer and electron transport pathway. In addition to TiO2, ZnO, SnO2 can be also used as electron transporting layers. The most used perovskite absorber is a CH3NH3PbI3 having a band gap of 1.55 eV. Various OIHP analogues with different organic cations or halides (i. e., CH3NH3PbI3-xClx, CH3NH3PbI3-xBrx, CH3NH3PbBr3, H2C(NH3)2PbI3, etc.) have been also studied as light absorbers because they have different optoelectronic properties as changing the composition. Hole transporting materials are various from commonly used spiro-OMeTAD, poly(triaryl amine) (PTAA), poly(3-hexylthiophene) (P3HT) and inorganic materials such as CuSCN, and CuI.

Tandem Solar Cells (TSCs)

A tandem architecture of solar cell consisting of two or more sub-cells which together convert more of the sunlight spectrum into electricity and therefore increase the overall cell efficiency. The sub-cells are connected on top of one another and can be constructed from different solar cells materials or from the same family of solar cells materials. However, they are constructed, the top sub-cell needs to absorb a different portion of the sunlight spectrum to that of the cell below. Perovskite is the perfect choice of top cell when combined with either silicon or CIGS bottom solar cells in that the perovskite top cell absorbs visible light but transmits infrared and near infrared light to the bottom cell. We have started working with academic and industrial coworker to realize our tandem solar cell. Our aim of using perovskite tandem devices as a straight path for the generalized use of third-generation PV technology requires enhancement of the efficiencies closer to the ones of Si cells.