太陽電池技術簡介. Outline 地球暖化問題. Environment Issues. Renewable energy. Introduction to solar cell. application. fundamental. Si solar cells 工業技術研究院綠能所張佳文研究員

Transcription

1 太陽電池技術簡介 工業技術研究院綠能所張佳文研究員 清大化工系能源科技與環境概論演講 101 年 1 月 11 日 ( 星期五 ) 下午 13:30 15:00 Outline Renewable energy Introduction to solar cell application fundamental Si solar cells 2013 年 1 月 11 日 Copyright ITRI 2013 Copyright ITRI Environment Issues 地球暖化問題 Copyright ITRI

2 能源分類 再生能源 新能源 ( 已可實用化, 但尚未普及 ) 再生能源自然界存在的能源可利用且可再生 枯竭性能源使用快完的能源 太陽光發電 太陽光發熱 風力 生質能 地熱 水力 海洋能 ( 溫度差 波力 潮汐等 ) 可半永久的利用 資源量充足 對環境無害 可抑制地球溫暖化 化石燃料 ( 煤 石油 天然氣 ) 核能 廢棄物 氫能利用 燃料電池 蓄熱等 便利 可利用的量有限 對後代威脅性增加 Copyright ITRI Energy Consumption (2011) 碳排放量較少的發電方式 再生能源 9% 太陽能 2% 地熱 2% 廢熱 5% 風力 13% 生質能 21% 再生能源 木頭 22% 水力發電 35% Copyright ITRI

3 太陽電池 Introduction 光伏电池 Solar Cell Photovoltaic Copyright ITRI 什麼是太陽電池? 可將光能轉換成電能

4 Solar Radiation Spectrum 入射太陽光能量 大氣層反射 雲反射 地表反射 大氣層吸收 大氣層頂端的陽光 海平面的輻射量 雲吸收 陸地及海洋吸收

5 Solar Spectrum 紫外光 可見光 紅外光 太陽光光譜 矽晶電池涵蓋 Solar Cell Applications Copyright ITRI Consumer Products Solar Jacket Charger Solar Fan Cap Solar Jacket Electronic Book Mobile Phone Solar Necktie Copyright ITRI Copyright ITRI

6 building-integrated PV (BIPV) Roof Facade Building-Integrated PV (BIPV) curtain wall in Aalst Hospital, Belgium Copyright Photovoltaic ITRI facade 2013 on Scheidegger Building, near Bern, Switzerland. 21 Copyright ITRI Photovoltaic Roof Tile Photovoltaic Energy Farm SRS Energy Solar Rail Techtile Energy Solar Window Blades Copyright ITRI 2013 The Technische Universitat from Darmstadt in Germany 23 EPV Solar Copyright ITRI

7 Solar Island floating in the sea Solar Tree Solar Cell Bags CSEM, United Arab Emirates Solar Forest-parking lots Milan Konarka Copyright ITRI 2013 Neville Mars 25 Copyright ITRI Solar Tents & Shelters Sunbrella Car Solar Window Solar Tents Copyright ITRI Copyright ITRI

8 Solar yacht Solar Motorcycle Solar Traffic Signs Solar Flight Solar Light Solar Bike Copyright ITRI 2013 NASA Dryden Flight Research Center 29 Copyright ITRI Solar Calculator Solar Watch World's First Solar Powered Stadium In Taiwan Taiwan recently finished construction on a solar-powered stadium that will officially open later this year to welcome the 2009 World Games. 8,844 solar panels 50,000 seat dragon-shaped 14,155 sq meter solar roof provide enough energy to power the stadium's 3,300 lights and two jumbo vision screens Solar Funny Stuff Copyright ITRI Copyright ITRI Photograph: Inhabitat.com

9 Photovoltaic Solar Cell Fundamentals Copyright ITRI Copyright ITRI How does a solar cell work? A solar cell delivers current to a load as long as the sun is shining Solar cell operating principles Solar cell operation is based on the photovoltaic effect: The generation of a voltage difference at the junction of two different materials in response to visible or other radiation. 1. Absorption of light - Generation of charge carriers 2. Separation of charge carriers 3. Collection of the carriers at the electrodes Copyright ITRI Copyright ITRI

10 pn-junction Electricity Generation To create an built-in electric field : join a p-type and an n-type semiconductor, to create a pn-junction. Here shown before ionization of the dopants; In the ionization process the free carriers will be (thermally) released to the surrounding semiconductor. p-n junction in thermal equilibrium w/ zero bias voltage applied. Electrons and holes concentration are reported respectively with blue and red lines. Gray regions are charge neutral. Light red zone is positively charged; light blue zone is negatively charged. Electric field shown on the bottom, the electrostatic force on electrons and holes and the direction in which the diffusion tends to move electrons and holes. What happens when the p-and n-type materials are brought together? Copyright ITRI Copyright ITRI Introduction to Solar Cell Technology What is p-n junction Creating a junction There are four main types of semiconductor junctions p-n p-i-n Schottcky barrier The electrons (-) collect in the N-layer. The holes (+) in the P-layer. When the outside circuit is closed, electricity flows. Copyright ITRI Heterojunction Copyright ITRI

11 p-n and p-i-n junction Structures of c-si and a-si solar cell P-N Junction Solar Cell P-I-N Junction Solar Cell Diffusion length of minor carrier in p-type layer Diffusion length of carrier in Intrinsic layer Device Type:Diffusion Device Generated Region:p-type layer (Minority carrier life time:10~20μs) Device Type:Drift Device Generated Region:Intrinsic layer Copyright ITRI Copyright ITRI Theory of I-V characterization Theory of I-V characterization V oc : 開路電壓 (V) I sc : 短路電流 (A) P max : 最大輸出功率 (W) V max : 最大輸出功率時之電壓 (V) I max : 最大輸出功率時之電流 (A) Isc I max 輸出功率 電流源 Pmax V max 電壓源 Voc Fill Factor (F.F.) = (V max I max / V oc I sc ) 100% 太陽電池效率 (Efficiency) = (P max / 輸入日照功率 ) 100% * 輸入日照功率 (W) = 太陽電池面積 (m 2 ) 日照強度 (W/m 2 ) * 日照強度為 1,000 W/ m 2 之最大輸出功率即為 W p Copyright ITRI Copyright ITRI

12 I-V Characteristics of Solar Cell Air Mass Air Mass is the measure of how far light travels through the Earth's atmosphere. Copyright ITRI Copyright ITRI 太陽電池種類 Solar Cell Efficiency 矽晶 矽薄膜 II-VI 族 單晶多晶 非晶非晶 / 微晶堆疊型 HIT 銅銦鎵硒玻璃 不銹鋼板 銻化鎘 矽晶片 III-V 族 III-V 族基板 染料敏化 玻璃 不銹鋼板

13 First Generation Single crystal silicon wafers (c-si) Polycrystalline silicon (poly-si) Bulk-Type 矽晶太陽電池 Larger Si wafer area than ICs Issues. thinner cells. simpler Si purification. higher conversion efficiency Inverted form of the PERL (Passivated Emitter and Rear Locally diffused) solar cell developed at UNSW based on the use of n-type silicon. Copyright ITRI Copyright ITRI How Solar Cells Work First Generation (Bulk Silicon) First generation photovoltaic cells are the dominant technology in the commercial production of solar cells, accounting for more than 86% of the solar cell market. Cells are typically made using a crystalline silicon wafer. Consists of a large-area, single layer p-n junction diode. Approaches Ingots can be either monocrystalline or multicrystalline Most common approach is to process discrete cells on wafers sawed from silicon ingots. More recent approach which saves energy is to process discrete cells on silicon wafers cut from multicrystalline ribbons Band gap ~1.11 ev Copyright ITRI Copyright ITRI

14 Crystal pulling: CZ method Crystal pulling: CZ method Copyright ITRI Copyright ITRI PV solar cell process PV solar cell process Copyright ITRI Copyright ITRI

15 Monocrystalline Silicon 單晶矽 Polycrystalline Silicon 多晶矽 Theoretical limit single junction cell Wafer 晶片 Cell 電池 The theoretical limit for a single pn-junction solar cell, E g =1.11eV: Efficiency~ 40.5% (direct illumination) Module 模組 Commercial silicon solar cells have an efficiency of 12-17%. (Lab record 25%) Copyright ITRI Copyright ITRI Second Generation: thin-film Thin Film Types 薄膜太陽電池 Thin-film Technologies. Silicon. amorphous. microcrystalline. polycrystalline. Chalcogenide (polycrystalline). CIS, CIGS [Cu (In,Ga) (Se,S)2]. CdTe. Dye sensitised, Organics Copyright ITRI Advantages. low materials cost. large manufacturing unit. fully integrated modules. aesthetics, ruggedness? Copyright ITRI

16 Thin Film Solar Cells Thin Film Solar Cells a-si:h CdTe CIGS η= 10.1% η= 17.3% η= 19.6% Glass ZnO:Alor SnO 2 :F p a-si:h Glass ITO or SnO 2 :F n CdS i-zno or ZnO:Al n CdS i n a-si:h(>1μm) a-si:h ZnO:Al p CdTe(>3μm) p CIGS (>2μm) Metal Metal Metal Glass Copyright ITRI Copyright ITRI Plasma Enhanced Chemical Vapor Deposition Thin Film Si Module Process Thin-film deposition Technique for depositing a thin film of material onto a substrate. Layer thickness can be controlled to within a few tens of nanometers Single layers of atoms can be deposited Chemical vapor deposition (CVD) Chemical process using a gas-phase precursor. Often a halide or hydride of the deposited element. PECVD -Plasma Enhanced CVD Uses an ionized vapor, or plasma, as a precursor Relies on electromagnetic means (electric current, microwave excitation) to produce plasma. Copyright ITRI Copyright ITRI

17 Laser structuring for monolithic inter-connections Integrated monolithic serial connection is a main advantage of thin film technology Low current and high voltage Accurate positioning and temperature control required because of thermal expansion of the glass substrate Thin Film Si Solar Cell Principle Copyright ITRI Copyright ITRI Thin-Film Silicon Cell Technology Introduction Crystalline silicon thin-film silicon Material issues Amorphous silicon Microcrystalline silicon Solar cell devices p-i-n solar cells Micromorph tandem cells Si Wafer PV Bulk absorber material: High quality silicon safe waferdeveloped by microelectronic semiconductor industry over50 yrs(not by PV!) PV cell technology: Front and back side passivation of wafer for internal electrical field and lighttrapping& contacting of wafer Thin-Film Si PV Substrate is a part of the deviceabsorber material needs to be deposited: Electronic properties Interfaces & structure Light-trapping Uniformity of layers Monolithic interconnection TCO (T, Haze, R sq ) High rate & good quality over large areas (m 2 ) Copyright ITRI Copyright ITRI

18 Comparison of Atomic Structure of c-si and a-si:h High quality Si Thin Films prepared by original Short-pulsed VHF plasma CVD method Schematic structure a-si:h μc-si:h Amorphous Silicon (a-si:h) Higher absorption coefficient at Visible and Shorter wavelengths with high photo to dark conductivity ratio (10 6 to 10 7 ) and less Si-H 2 bond mode (less than a few at.%) Copyright ITRI Micro-Crystalline Silicon film (μc-si:h) High absorption coefficient at Longer wave lengths with homogeneous crystallinityover a square meter size substrate Copyright ITRI The Amorphous p-i-n Solar Cell: ~0.3 mm Thickness Deposition of Amorphous Silicon Amorphous silicon is deposited by a plasma process from a mixture of silane and hydrogen Plasma deposition parameters influence the quality of the layers High frequency RF increase plasma energy and deposition rate Copyright ITRI Copyright ITRI

19 Transition to Microcrystalline Silicon by Hydrogen Dilution Microcrystalline Silicon p-i-n Solar Cell Institut de Microtechnique Neuchâtel in 1994 World-wide first thin film c-si cell deposited at 200 o C E. Vallat-Sauvain et al., Advances in Microcrystalline Silicon Solar Cell Technologies (2006) Copyright ITRI Copyright ITRI μc-si:h Solar Cells: Spectral Response and Jsc Micromorph Tandem Cell Concept (IMT Neuchâtel 1994) Spectral Response (a.u.) Wavelength Typical QE depends on Collection Cell thickness Light-trapping Short-circuit current obtained: J SC 20 to 30 ma/cm 2 for i- layer thicknesses of 1-3 μm Optimal Bandgap Combination for tandem cells: 1.1 ev & 1.7 ev T.J. Coutts et al., PVSEC-12 Copyright ITRI Copyright ITRI

20 Spectral response of an a-si/μc-si tandem cell Future Trends to Improve Efficiencies More and more complex stacked structures (> 15 layers) for enhanced efficiency Challenge for industrial isation: Build universal PECVD reactors for deposition of very thin individual functional layers Bandgap μc-si: ~ 1.1 ev(1130 nm), Bandgap a-si: ~ ev( nm) Better utilization of the solar spectrum Copyright ITRI Copyright ITRI Thank you for your attention 張佳文 changcw@itri.org.tw (03)