混合式奈米碳管/矽蕭特基接面太陽能電池

Abstract

奈米碳管擁有優異的電學及光學特性，並且可用低廉的價格大量製造，因此自從奈米碳管於1991年被發現後，就被大量應用在製作電子及光學組件和設備。在本論文中，我們將高穿透及高導電度的多壁奈米碳管與利用水溶液製程的混合型矽基蕭特基接面太陽能電池結合，製作出擁有高光電轉換效率、且能夠以低於150°C進行製程的矽基太陽能電池，在製程的過程中不需要高真空環境，不但能降低製程成本，更同時符合未來矽基板薄化及便宜化的趨勢。 在本論文中的研究中，我們首先將奈米碳管塗料應用於以矽奈米線及矽金字塔結構為基底的混合型矽基太陽能電池，並進行製程的優化，同時與PEDOT:PSS做比較，優化的製程包括矽奈米線長度、退火溫度及銀正電極的遮蔽率，由於奈米碳管擁有較PEDOT:PSS更佳的的穿透及導電性，因此在各項優化製程下，奈米碳管元件都較PEDOT:PSS有更佳的效率表現，在銀正電極遮蔽率14%、退火溫度150°C及矽奈米線長度為150奈米的最佳製程條件下，使用奈米碳管的混合型矽基太陽能電池分別在矽奈米線及矽金字塔結構得到13.82%及11.90%的高轉換效率，而PEDOT:PSS在兩種基板上最高僅有12.96%及7.43%的轉換效率。為了抑制元件背部載子的復合，我們進一步透過刮刀製程在矽基板和鋁背電極之間塗佈一層有機水溶性小分子材料Alq3或是OXD-7作為電洞阻擋層，Alq3及OXD-7在以奈米碳管為材料的矽奈米線元件分別得到13.92%和14.41%的最佳轉換效率。最後我們對混合型太陽能電池的壽命進行測試，發現奈米碳管元件經過9-10天效率才會衰減至原本的一半，超過PEDOT:PSS元件的3-6天，衰減的速度取決於氧化層生長速度。

Carbon nanotubes (CNTs) possess superior optical and electrical properties and can be produced massively at relatively low cost. Therefore, since their discovery in 1991, CNTs have found many applications for electronic/optoelectronic devices and components. In this work, the highly transparent and conductive multi-wall- (MW-) CNTs are employed to realize solution-processed, hybrid silicon (Si) Schottky -junction solar cells. As long as a high power conversion efficiency (PCE) is ensured, manufacturing Si-based solar cells at temperatures below 150 °C without high vacuum conditions not only significantly lowers the fabrication cost, but also enables the use of ultrathin substrates to save on the material cost for the future. In this thesis, we first describe the optimization of device structures on silicon wafers with nanowire and micro-pyramidal surface textures, and compare the device characteristics with those of hybrid cells based on Si and poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS). The optimized processing conditions include the length of silicon nanowires, the annealing temperature, and the shading ratio of the frontal silver grids. It is found that the hybrid CNT cells outperform the hybrid PEDOT:PSS counterpart under individually optimized processing conditions due to better transparency and conductivity of CNTs than PEDOT:PSS. The best hybrid CNT cells, fabricated using a 14% grid shield ratio, 150 °C annealing temperature, and 150nm nanowire length, achieve a PCE of 11.90% and 13.82% in micro-pyramid and nanowire (NW) textured silicon, respectively, in contrast to 7.43% and 12.96% for hybrid PEDOT:PSS cells. To control the rear surface recombination, we further employ two solution-processed, small-molecule materials, Tris(8-hydroxyquinolinato) aluminium (Alq3) and 1,3-bis(2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl) benzene (OXD-7) via a blade-coating technique between the silicon wafer and aluminum electrode. As a result, the PCE of hybrid CNT/Si NW solar cells is enhanced to 13.92% and 14.41% with the insertion of the Alq3 and OXD-7 rear interlayer, respectively. Finally, the lifetime of the hybrid solar cells is studied, where the PCE of CNT cells is degraded in half in 9-10 days, surpassing that of PEDOT:PSS cells in 3-6 days depending the growth rate of an interfacial oxidation layer.