藉由表面電場以及背電場製備高效率PEDOT:PSS/ GaAs太陽能電池與PEDOT: PSS/Si介面特性研究

Abstract

本論文可分為兩大主軸： (1)藉由X光光電子光譜，發現位於介面上的PEDOT未飽合碳接上了一個拉電子基團，同樣的Gaussian計算的結果顯示PEDOT的HOMO跟LUMO主要集中在PEDOT的未飽合碳上，因此，發生化學反應應該會發生在未飽合碳上。因此，藉由Gaussian、VASP以及X光光電子光譜認為PEDOT會和二氧化矽的氧或矽進行反映。 (2)雜參濃度為1016 cm-3的n-type GaAs，旋轉塗佈上PEDOT:PSS就可以得到8.4 %效率。之後，利用分子束磊晶的方式產生出背電場，將效率提升到9.87%；利用磊晶的方式在表面加上雜參濃度1019 cm-3 的p-type GaAs產生出表面電場可以提高效率至11.86%。利用雜參濃度高的區域以及雜參濃度低的區域製備出來的高分子/GaAs太陽能電池會在不同濃度的介面產生出電場，可以加速電子-電動對的分離並且產生出少數載子的位障，進而減少載子複合，增加光電流。另外，FF從0.7提升到0.8以及Voc從0.69 V 提升至0.77 V。

Research work presented in this thesis is divided into two parts: (1) to investigate the interface of PEDOT:PSS/Si using X-ray photoelectron spectroscopy and simulations. (2) to enhance the efficiency of PEDOT:PSS/GaAs solar cells by using front-surface and back-surface field.

(1)In this study, results from X-ray photoelectron spectroscopy indicate that the unsaturated carbons of PEDOT are bonded with the electron-withdrawing groups. The Gaussian simulations also show that the HOMO and LUMO levels of the PEDOT are mostly contributed from the unsaturated carbons. Therefore, chemical reactions are most likely to take place on those unsaturated carbons. Based on preliminary results from X-ray photoelectron spectroscopy, Gaussian simulations, and VASP calculations, we speculate that the unsaturated carbons on the PEDOT interact with oxygen or silicon atoms of the silicon oxide.

(2)Planar hybrid solar cells based on bulk GaAs wafers with a background doping density of 1016 cm-3 and poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate), which demonstrated an excellent power conversion efficiency of 8.46%. The efficiency of the cell was enhanced to 9.87% with a back-surface field feature using a molecular beam epitaxially grown n-type GaAs epi-layer. The efficiency and fill factor reaches a record high 11.86% and 0.8 when an additional p+ GaAs epi-layer is deposited on the surface of the solar cells to provide a front-surface field. The demonstrated hybrid solar cells that combine GaAs and conjugated polymers at low temperatures provide a possible alternative technology to simplify fabrication processes and reduce costs.