Tandem Perovskite Solar Cell

[Music] I'm a - rajagopal currently a graduate student in djenne research group at University of Washington in this video I will explain the fundamentals and exciting prospects of Paris cat tandem solar cells which has been the focus of my research over the last couple of years generation of electricity from clean and renewable energy sources is important for meeting our global energy demands in a sustainable manner the graphic here shows the total reserves remaining for different non renewable sources in comparison to the yearly potential of renewables it is clear that solar energy surpasses by order of magnitude the potential of all other renewable alternatives combined technological advancements have continually decreased the price of solar power and increase the global installation of solar panels however solar power is still expensive compared to conventional energy sources and contributes only to a minuscule fraction of total energy generation a typical photovoltaic system used for generation of electricity from sunlight is comprised of a solar module inverter and several other support components currently the solar module itself contributes to more than 50% of the total cost therefore development of modules with lower manufacturing cost and higher efficiency is crucial to drive down the cost of solar power in future one of the key metric used to assess the potential of a solar cell technology is power conversion efficiency it is the ratio of the energy output from solar cell with respect to the input energy from Sun solar cell technologies have evolved with the discovery and emergence of new semiconductor absorber materials solar cells based on inorganic wafers such as silicon and gallium arsenate constitute first generation technologies solar cells based on inorganic thin films such as 6 and cadmium telluride constitute second-generation technologies these technologies have the merit of high efficiencies over 20% but require the use of high cost processing techniques on the other hand third generation solar cell technologies based on organic thin films have relatively lower efficiencies around 12% but can be easily processed at lower costs recently a new solar cell technology based on organic inorganic hybrid perovskite has emerged perovskite solar cell technology embodies both high efficiency and low cost regardless of the technology a single Junction solar cell comprises an absorber layer sandwiched between positive and negative contacts essentially as the sunlight hits solar cell the light is converted to electrical carriers in the absorber layer and extracted by the contacts the incident sunlight consists of different energies ranging from infrared to visible to ultraviolet let's have a deeper look into the functioning of a solar cell to understand different losses absorber layer is a semiconductor with a characteristic bandgap denoted as eg here energy is equal to or greater than the bandgap or absorbed and creates electrical carriers energies below the bandgap are not absorbed and leads to below band gap loss for energy is greater than the bandgap a fraction is lost because of the thermal relaxation and weeds to thermalization loss in this view let's consider two different cases of silicon and perovskite solar cells silicon solar cell which has a lower band gap has lowered below bandgap loss and higher thermalization loss on the other hand for a perovskite solar cell which has a higher bandgap has higher below bandgap loss and lower thermalization loss the balance of losses constraints realizable efficiency for single-junction solar cells and is given by the shockley-queisser efficiency calculations with a maximum efficiency around 30% achievable using 1.1 to 1.4 evey bandgap current record efficiencies for silicon and perovskite solar cells are approaching the Eskew limit so how can we surpass the SQ element one of the most promising approaches to realize higher efficiencies is multi Junction or tandem solar cells a multi Junction solar cell has absorbers with different band gaps tagged in a device in this way higher energies are absorbed in different large bandgap sub cell and the unobserved low energies are absorbed in the back small bandgap sub cell as a result both below band gap and thermalization losses are greatly reduced and results in an improved light harvesting thus compared to a single Junction solar cell an increased power output is possible in multi-junction solar cells due to reduce losses the theoretical limit for multi Junction solar cells increase with the number of band gaps used in a device even in the simplest case of two junctions the efficiency limit of 42 percent is significantly higher than the 30 percent SQL limit for single Junction solar cells the concept of multi Junction solar cell was first proposed in 1980s and since then successful demonstrations based on in organic solar cell technologies have led to impressive efficiency records up to 46% that said these state-of-the-art multi-junction solar cells in more complex processing and are very expensive ultimately inhibiting their use for terrestrial applications this is where perovskite solar cells provide a unique opportunity they can be easily manufactured by roll-to-roll printing approaches at very low cost making them attractive for both large scale grid integration and small-scale niche applications the efficiency of a single Junction perovskite solar cell has rapidly evolved in last five years and the current record is 22.7% which is comparable to other matured inorganic technologies these exacting attributes are result of inherent material characteristics of hybrid Paris gets the ABX 3 perovskite crystal structure offers enormous flexibility with a broad compositional space typically a is organic cation B is metal cation and X is halogen an ion pair of skates have excellent opt electronic properties including strong absorption with sharp absorption onset ultra-fast charge generation and long charge transport all of them very important for efficient conversion of sunlight into electricity Paris kites can be processed using numerous processing routes suitable for low-cost printing at scale the combination of this incredible structure property processing aspect leads to very high performance of perovskite solar cells additionally bandgap of Paris cars can be tailored by compositional engineering the most commonly employed methylammonium lead iodide perovskites has a band gap of 1.6 evie metal site allowing facilitates band gap lowering with values up to 1.2 Eve II realized using lead tin alloys halide site allowing facilitates band gap widening with values up to 2.3 Eve II realized using iodine bromine allows a combination of low cost easy processing high efficiency and facile tunability thus makes Piroska tandem solar cells highly promising tandem solar cells can be made in either for terminal or two terminal configuration in for terminal sub cells are mechanically stabbed on top of each other this involves a simpler assembly but are expensive due to added components contrastingly in two terminal sub cells are electrically connected this requires current matching between sub cells but are relatively cheaper both configurations have potential to provide efficiencies close to 40 percent to terminal configuration has a greater sensitivity for bandgap combination because of the current matching requirement Facel bandgap tuning of perovskites open a wide range of possibilities CA a solar cell with a low bandgap of one evey can be used in tandem with a large band gap perovskite and has the maximum efficiency potential the two sub cells are connected in series by an interconnecting layer alternatively commercially use silicon solar cell with 1.12 evey bandgap can also be used in tandem with perovskite solar cells to further improve their efficiencies in the other extreme a small bandgap arrow skate around 1.2 evie can be used in tandem with a large band gap peroxide to form perovskite barosky tandem solar cells my research has been mainly focusing on development of perovskite Piroska tandem solar cells and Cas Piroska tandem solar cells let's take the example of perovskite Piroska tandem and look into the key components and fabrication process a tandem device essentially combines a small bandgap and large bandgap single Junction perovskite solar cell the basic components of a solar cell include absorber layer charge transport inter layers a transparent electrode in the front and an opaque electrode in the back the additional component in a tandem device is the inter connecting layer which connects sub cells in series thus in a tandem solar cell voltage is the sum of sub cell voltages and current is the minimum of sub cells the first step in the fabrication of a Piroska tandem is patterning of indium tin oxide coated glass via itching next different layers in large bandgap subcell are deposited using spin coating this is a picture of a typical spin coater in spin coating a small amount of coating material is applied at the center of the substrate and then the substrate is rotated at high speed for spreading the material and evaporating the solvent performance infants next I do layer is deposited by a sputtering this is a picture of the sputter unit and the figure insert shows the plasma glow discharge within the chamber during Operation sputtering process basically involves the use of argon ions to bombard and eject atoms from the target surface which gets deposited on the substrate to form thin films next different layers in small bandgap sub cell are deposited using spin coating finally the silver metal electrode is deposited using thermal evaporation this is a picture of thermal evaporator system and the figure insert shows the geometry of source electrodes inside the chamber thermal evaporation process essentially involves resistive heating of the source material which creates vapour particles that gets deposited on the substrate to form thin films this is a photograph of a final tandem device and an image of the device cross-section taken using a scanning electron microscope the demarcation of different layers and sub cells can be clearly seen the last couple of years our research advances on both material and device level have led to exciting progress in development of small bandgap large band gap and tandem perovskite solar cell through this effort we were able to achieve record performance metrics recently key results can be found in these highlighted publications thank you

Channel: UW Clean Energy Institute

Views: 25,062

Keywords: perovskite, tandem, solar, efficiency

Id: JAkQnUENw-k

Length: 11min 40sec (700 seconds)

Published: Thu May 17 2018