單晶矽太陽能電池製程改善及退火處理之研究

The Process Improvement and Annealing Treatment of a Single-Crystalline Silicon Solar Cell

劉時郡(Shi-Jun Liu)

指導教授 ： 林天財

崑山科技大學/工程學院/電機工程研究所/碩士(2007年)

https://doi.org/10.6828/KSU.2007.00043

摘要

近年來由於原油價格高漲不下，太陽能電池為熱門替代能源，本研究主要以不同離子佈植濃度、不同基板厚度與阻值，經過爐管退火後來探討對太陽能電池元件特性之影響。
研究結果顯示，在逆字金塔底部面積為40*40um間隔5um時，可得最佳反射率4%，比平面反射率降低十倍之多，可使太陽能電池效率提升。磷板擴散製作太陽能電池需要高溫與長時間的擴散，而光電特性才會較理想。離子佈植n層需要高濃度，讓電極區域之串聯電阻降低，使短路電流增加，佈植磷濃度為1.6x1020cm-3是較適宜之參數，而BSF構造因為障壁電場的關係使PP+區內少數載子(電子)被反射，不會在電極處與多數載子(電洞)複合，可以改善長波長之波段而增加光電流。矽晶圓在經過離子轟擊之後，晶格呈現混亂，內部結構需要經過退火處理，使晶格重新排列而回復到單晶結構，由實驗發現1000°C為較佳退火溫度，而退火時間增長，會讓表面濃度些微降低，但是pn接面深度會急遽增加，接合處太深會讓在表面所生成之少數載子不易到達，相對地短波長的光子並不能有效轉換成光電流，發現一小時為較佳退火時間。在磷重摻雜n+層之下，會形成矽單陡接面，因為空乏區大小造成高阻值100Ω-cm晶圓之光電特性較阻值為10Ω-cm佳，即使退火時間增長也是相同結果。
實驗發現1000A厚度之二氧化矽是作為抗反射層較佳的厚度，增加抗反射層太陽能電池相對表面複合降低，光電流表現較佳。當基板厚度為200um時，能讓多數載子順利到達電極處，讓擴散長度增大，避免在傳導過程中被複合，所以載子壽命增大，而短路電流也隨之增大。正面佈植磷濃度在1.6x1020cm-3，固定退火條件1000°C一小時，在照度25mW時會有最高效率1.41%。

關鍵字

逆金字塔結構 ； 太陽電池 ； 單晶矽

並列摘要

Since the crude oil price is so expensive and not reduced in recent years, the solar cell becomes the hottest alternative energy source. This research mainly focuses on the influence of the characteristic of solar cell after the anneal process by taking the different concentration of ion implantation, different silicon substrate’s thickness, and resistance value of wafers.
The result shows that the area of anti-pyramid bottom is about 5um of 40*40um, the lowest reflectivity is 4%, which is ten times less then the reflectivity of plate and exhibit a better solar cell energy efficiency. To make a ideal solar cell, which has better photoelectric characteristic, needs long-term diffusing process and high temperature by producing the diffusing phosphorus plate.
The high concentration of ion implanting n layer reduces the series resistance in the electrode area and increases the short current. In this case, the proper ion implantation concentration of phosphorus is 1.6x1020cm-3. Moreover, due to the electric field barrier of BSF structure, few carriers in PP + region is reflected and majority carrier (of holes) will not be recombined in the electrode place. All these improve the absorption of long wavelength band and increase the photocurrent. After ion implantation, the crystalline of the silicon wafer appears lattice disorder, and the inside structure needs annealing to make the crystalline reconfigured and afresh to a single crystal structure.
The results show that the annealing temperature 1000°C is the better condition and the better annealing time is one hour. If the annealing time is increased, the concentration at surface would be reduced slightly, and pn junction would be increased rapidly. On the other hand, if the junction of pn is too deep, carrier is hard to arrive at electrode.
The photon with short wavelength would not exchange to photocurrent effectively.
Under the layer of heavy-dopant phosphorus n + layer, there forms the silicon one-sided abrupt junction. The photoelectric characteristic of high resistance wafer(100Ω-cm) which has wide depletion region is better than lower resistance wafer(10Ω-cm) . Even if the annealing time of annealing increases, it also gets the same result.
It was also found that the silicon of oxidizes of 1000 A is the better thickness as anti-reflecting layer.Once to add anti-reflecting layer, the relative surface recombination of solar cell would be reduced, and the performance of photocurrent would be better.
When thickness of the silicon wafer is 200 um, the majority carrier can reach the electrode easily. The diffusion length of carrier would be increased, and the carrier would not be recombined in the transportation to electrode. That is the reason why the life-time of carrier would increase, and short current also increase.
The fixed condition is 1000°C and one hour, and P implanting concentration is 1.6x1020cm-3. The device has a high efficiency of 1.41% in the intensity of illumination of 25mW.

並列關鍵字

Solar Cell ； Single-Crystalline Silicon ； Pyramid structure

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