Improving the efficiency of PbS Schottky Solar Cell by Tuning Size and Interface of Nanocrystals

• Main Authors: Bei-Chi Chang, 張倍綺
• Other Authors: Chia-Chun Chen
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/36073198329097244529

碩士 === 國立臺灣師範大學 === 化學系 === 101 === This thesis focused on two parts: (1) Improving solution process synthesis of Ⅳ-Ⅵ lead sulfide (PbS) semiconductor quantum dots (QDs). (2) Fabricating Schottky solar cells based on PbS nanocrystals and optimizing the efficiencies of PbS Schottky photovoltaic device. First, the syntheses of PbS QDs with different sizes were obtained by using different proportion of OA-PbO and controlling temperature. The different diameter of PbS quantum dots were 3, 3.5, 4 and 5.6 nm, respectively. Finally, the high yield of PbS nanocrystals with small size (~ 3.5nm) was also obtained by using the mixed solvent approach with high-speed centrifugation. The PbS quantum dots with small size have the first exciton energy is 1.44eV due to quantum confinement effects. The PbS quantum dots with small size were applied to fabricate PbS NCs Schottky solar photovoltaic device which is based on structure of ITO / PEDOT: PSS / PbS / Al. The device demonstrated high open circuit voltage (~ 0.43eV) and large short circuit current density (~ 12.5mA/cm2). The overall efficiency of PbS Schottky solar cell was improved and reached to 2.02%. To optimize the efficiency of PbS NCs Schottky Solar cell, the PEDOT: PSS polymer film was used as a hole transported layer between ITO and PbS NCs film. According to analysis of AFM and SEM measurement, the PEDOT: PSS polymer film smoothed the ITO substrate and lower roughness. Therefore, the yield rate of PbS NCs devices was increased. Second, the high short-circuit current density was obtained by tuning appropriate thickness of PbS NCs film which caused high absorption ability and reduced the recombination of electron-hole pair. Because the as-synthesized PbS NCs were usually passivated with ~2.5 nm long alkyl ligands (OA), which may prevent close nanocrystal packing of PbS thin films and thus, impede charge transport. The PbS NC films were treated by ethanedithoiol (EDT) to remove the long chain ligands from NC surfaces and reduce interparticle spaces of NCs, resulting in improve the carrier transport ability of the photovoltaic device. Finally, the electrical property of PbS NCs thin film was affected by thermal annealing process. We found that the surface functional groups of PbS NCs can be desorbed during thermal annealing process, resulting in decreased distance between the quantum dots to increase the conductivity of the film. During thermal annealing process, deep traps (PbSO4) in PbS NCs were found and reduced the recombination of electron-hole pair. Overall results showed that to the quality of NCs and device structures can be improved by controlling various condition. The best photoelectric conversion efficiency was up to 2.52％.