上理 第二讲 太阳能电池基本原理.ppt

V I Power is either generated or dissipated, depending on the quadrant you are in. 1ST Quadrant: Dissipation 3D Quadrant: Dissipation 2ND Quadrant: Generation 4TH Quadrant: Generation I V Dark Characteristic Light Characteristic I V Power Generating Region Power Dissipating Region Power Dissipating Region 光照能使电池的I-V曲线向下平移到第四象限，于是二极管的电能可以被获取。 为便于讨论，太阳电池的I-V特性曲线通常被上下翻转，将输出曲线置于第一象限，并用下式表示： The VI characteristic of a solar cell is usually displayed like this: V I V I The coordinate system is flipped around the voltage axis. 用于衡量在一定照射强度、工作温度以及面积条件下，太阳能电池电力输出的两个主要制约参数为： 短路电流（Isc， Short circuit current ） 当电压为零时电池输出的最大电流，Isc=IL。Isc与所接受到的光照强度成正比。 开路电压（Voc， Open circuit voltage ） 电流为零时，电池输出的最大电压。Voc的值随辐照强度的增加成对数方式增长。 I = ISC R = 0 Does it surprise you that the current at short circuit is not infinite? Or that a current can flow with no voltage? Where does the energy originate? Question #1: I = 0 R = ? Question #2: + _ V = VOC RS , RSH ISC VOC The slopes of these lines are characteristic resistances. RSH RS ISC RS RSH RLOAD Equivalent circuit for a solar cell with load. Internal resistances RS and RSH represent power loss mechanisms inside the cell. Cell Cell ISC RS = 0? RSH = ? RLOAD The ideal solar cell would have no internal losses at all! What would the VI characteristic of THIS cell look like? ISC VOC RSH = ? RS = 0 The Ideal Solar Cell Notice that the area under the rectangle = PMAX for the ideal cell. For this cell, PMAX = VOC ? ISC ISC VOC The Ideal Solar Cell 对于I-V曲线上的每一点，都可取该点上电流与电压的乘积，以反映此工作情形下的输出电功率。 填充因子（FF，Fill Factor）是衡量电池P-N结的质量以及串联电阻的参数。 填充因子定义为： 所以： ISC , PMAX , VOC (0.5V, 0 mA) ? V ? I = 0 mW (0.43 V, 142 mA) ? V ? I = 61 mW ISC VOC PMAX (0V, 150 mA) ? V ? I = 0 mW Some typical values ISC VOC Fill Factor In fact, PMAX/(ISC ? VOC) measures the cell’s quality as a power source. The quantity is called the “Fill Factor.” Can you see why? 2、 本征半导体 完全纯净的、具有晶体结构的半导体，称为本征半导体。 晶体中原子的排列方式 硅单晶中的共价健结构 共价健 共价键中的两个电子，称为价电子。 Si