DLC has been attractive as semiconductor materials for solar cell due to its biological friendliness, flexible microstructures, and especially its tunable band gap. In order to fabricate high-efficiency multiband gap solar cell, it is important to control the sp3/ sp2 bonds ratio of DLC film corresponding to optical band gap (Eg). There are many references reporting the relations among the fabrication conditions, Eg, sp3/ sp2, and ID/ IG. However, a more comprehensive database is needed for controllable fabrication. Especially, the quantitative relationship of sp3/ sp2 ratio to Eg of DLC film by PECVD is unclear. In this paper, 36 sets of DLC films were fabricated by RF-PECVD. Characterization methods of XPS, Raman spectroscopy, and IR absorption have been used to determine the sp3/ sp2 ratio of DLC films. UV/visible light absorption method has applied to evaluate Eg. The Eg obtained is in the range 1.45–3.0 eV. Our results agree well with the references. The XPS spectra gives a linear relationship as Eg = − 0.161 (± 0.136) + 26.095 (± 1.704) · {sp3 (XPS)/sp2}, the Raman spectra shows a linear function that Eg = 1.327 (± 0.046) + 0.428 (± 0.036) · (ID/IG), as well as the FTIR analysis demonstrates that Eg = − 0.492 (± 0.093) + 0.464 (± 0.044) · {sp3 (FTIR)/sp2}.

Carbazole과 diketopyrrolopyrrole를 기본 골격으로 한 2,5-bis-(2-butyl-octyl)-3,6-bis-[5-(4-carbazol-9-ylphenyl)-thiophen-2-yl] -2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione (PCTDPP12)을 스즈키 커플링 반응을 이용하여 합성하였다. UV-Visible 분광법으로 확인 한 결과 PCTDPP의 용액과 필름의 최대 흡수 피크는 각각 643 nm와 671 nm이며, PCTDPP12의 광학적 밴드갭은 각각 1.84 eV이다. 열처리에 의해 PCTDPP12의 UV-visible 흡광도 및 최대 흡수 파장이 변화된는 것을 관찰 하였다. 그리고 순환 전압 전류법에 의해 조사한 PCTDPP12의 HOMO 및 LUMO 에너지 준위는 –5.34 eV와 -3.54 eV 이다.

Taguchi methodology has been applied to get an idea about the parameters related to the chemical vapour deposition technique, which influences the formation of semiconducting carbon thin film of a desired band gap. L9 orthogonal array was used for this purpose. The analysis based on Taguchi methodology suggests that amongst the parameters selected, the temperature of pyrolysis significantly controls the magnitude of band gap (46%). Sintering time has a small influence (30%) on the band gap formation and other factors have almost no influence on the band gap formation. Moreover this analysis suggests that lower temperature of pyrolysis (≤ 750℃) and lower time of sintering (≤ 1 h) should be preferred to get carbon thin film with the desired band gap of 1.2eV.