硒化銅銦鎵薄膜太陽電池之光吸收層薄膜製備及特性分析

為了降低電池元件生產成本，使用非真空製程製備太陽電池已成為近年來熱門的研發方向。因此，本研究將以非真空塗佈法製備Cu(In,Ga)Se2光吸收層薄膜。論文中改變前驅溶液之配方，製備含奈米粉體之前驅溶液、含硒離子之前驅溶液以及含鉍離子之前驅溶液，亦利用晶種層進行Cu(In,Ga)Se2薄膜特性之改善。論文首先選擇化學還原製程於常溫常壓下製備前驅奈米粉體，此技術不須再經過含有還原氣氛下壓燒即可得到具晶相之合金粉體，並將奈米粉體塗佈前驅薄膜搭配硒化法製備緻密之Cu(In,Ga)Se2光吸收層薄膜，文中探討其生成機制，透過奈米粉體之使用有效降低Cu(In,Ga)Se2合成溫度至450度。另外藉由化學還原法亦可直接進行銅銦鎵硒奈米粉體之製備，此技術不須再經過含有硒蒸氣氣氛下壓燒即可得到銅銦鎵硒化合物。再將硒化物粉體經塗佈和煆燒即可得到大粒徑且緻密性良好之Cu(In,Ga)Se2光吸收層薄膜。為了增加薄膜均勻性，第二部份使用溶液法製作前驅薄膜，並選用亞硒酸做為硒源，藉由亞硒酸之使用，達成硒源與其他元素均勻混合之目的。文中探討以亞硒酸作為硒源合成Cu(In,Ga)Se2光吸收層薄膜之生長機制。另一方面，文中亦針對不同硒源添加方式對Cu(In,Ga)Se2光吸收層薄膜合成之影響進行研究。研究顯示直接使用硒溶液容易生成過厚之硒化鉬，將抑制Cu(In,Ga)Se2相生成和晶粒之生長，導致電池元件特性的下降。使用硒蒸氣作為硒源可以避免過厚之硒化鉬生成且製備出特性良好之Cu(In,Ga)Se2光吸收層薄膜。因此利用硒蒸氣作為硒源可大幅提升Cu(In,Ga)Se2電池元件效率。為了提升Cu(In,Ga)Se2薄膜之電性，第三部份添加五族元素離子進行Cu(In,Ga)Se2光吸收層薄膜之改質，Cu(In,Ga)Se2合成溫度會由500oC降至450oC, 且隨著五族元素離子濃度的增加，薄膜粒徑亦隨之增加，此乃由於其中間產物具有助熔效應所致。低溫光激發光光譜儀量測顯示一發光峰值，為施子能階與授子能階躍遷所造成，添加五族元素離子會造成施子缺陷量減少，使光激發光發光強度下降，而薄膜載子濃度增加。因此可透過適當Bi3+的添加， Cu(In,Ga)Se2光吸收層薄膜之電性由4.37%提升至6.29%。為進一步提升Cu(In,Ga)Se2薄膜之電性，論文第四部份選擇In2Se3作為晶種層製備Cu(In,Ga)Se2光吸收層薄膜。In2Se3層具有(006)及(300)之晶面，研究發現隨不同晶面In2Se3層之使用，光吸收層薄膜其(112)晶面對(204/220)晶面之X光繞射相對強度亦隨之改變。可藉由具(006)晶面之晶種層來達成具(112)晶面之Cu(In,Ga)Se2光吸收層薄膜之生長；另外藉由具(300)晶面之晶種層來達成具(204/220)晶面之Cu(In,Ga)Se2光吸收層薄膜之生長。當使用具(112)晶面之Cu(In,Ga)Se2光吸收層薄膜，其電池元件擁有7.00%之轉化效率。本論文針對不同前驅溶液製備之Cu(In,Ga)Se2薄膜進行結構及電性特性分析，利用前驅溶液所添加成分之改變，改善薄膜型態，提升薄膜結晶性，以及增加薄膜之載子濃度，有效提升電池元件效率，增加Cu(In,Ga)Se2光吸收層薄膜在太陽電池市場之發展潛力。

關鍵字

硒化銅銦鎵；薄膜太陽電池；光吸收層薄膜

並列摘要

In this work, metal compounds, selenide compounds, selenium-containing solutions, and the bismuth-containing solutions were applied as the precursor pastes to promote the grain growth and improve the electrical properties of the films. The photovoltaic characteristics of the fabricated solar cells were investigated. Cu(In,Ga)Se2 films were successfully prepared from the nanoparticles that were synthesized via the chemical reduction reaction using ethylene glycol as the solvent and NaBH4 as a reducing agent in an ambient atmosphere. The route developed not only reduced the synthesis temperature of the chalcopyrite compounds to 450oC, but also controlled the phases of the formed products. This developed process was also applied for preparing selenide compounds. The presence of selenide species in the precursors enlarged the grains upon heating, and densified the prepared films. In the second section, H2SeO3 was used as an Se source in the starting solution, leading to an improvement in homogeneous mixing in the precursor pastes. H2SeO3 is first decomposed to yield selenium species at elevated temperatures. Subsequently, In2Se3 is formed from selenium and indium species. Finally, In2Se3 reacts with other species to yield Cu(In,Ga)Se2. Furthermore, various routes to incorporate selenium ions were examined. The formation of thick MoSe2 films tended to retard the formation of Cu(In,Ga)Se2 and decrease the grain size of the prepared films. The selenium ion-containing solutions coated on the top layer of Cu(In,Ga)Se2 precursor films would be easily evaporated during the heating process, therefore causing a decrease in the thickness and the porous microstructures of the films. In the third section, the influence of doping with group V ions in the properties of synthesized Cu(In,Ga)Se2 films was investigated. The incorporation of group V ions in Cu(In,Ga)Se2 significantly increased the size of the grains in the obtained films, and decreased the film roughness. The intermediate compound was thought to react with selenium vapor to form selenide compounds, which acted as a flux agent at elevated temperatures. The low-temperature photoluminescence spectra of group V -containing Cu(In,Ga)Se2 films revealed attenuated intensity of the peak that was attributed to the donor-acceptor pair transition following the incorporation of group V ions. The efficiency of solar cells increased from 4.37% to 6.29% as group V-ion doping amount was increased from 0 to1.0 mol%. In the fourth section, In2Se3 films were applied as the seeding layer for synthesizing Cu(In,Ga)Se2 films. Due to the crystalline symmetry, the preferred (112)-oriented Cu(In,Ga)Se2 film was produced using the preferred (006)-oriented In2Se3 seeding layers. On the contrary, the (220/204)-oriented Cu(In,Ga)Se2 films were yielded employing the (300)-oriented In2Se3 seeding layers. Using the (112)-oriented Cu(In,Ga)Se2 films resulted in increasing the conversion efficiency of the device to 7.0%. Well controlling the precursors used in the pastes not only increased the characteristics of the films but also improved the conversion efficiencies of the solar devices.