The BCBJ (Back Contact and Back Junction) or back-lit solar cell design eliminates shading loss by placing the pn junction and metal electrode contacts all on one side that faces away from the sun. However, as the electron-hole generation sites now are located very far from the pn junction, loss by minority-carrier recombination can be a significant issue. Utilizing Medici, a 2-dimensional semiconductor device simulation tool, the interdependency between the substrate thickness and the minority-carrier recombination lifetime was studied in terms of how these factors affect the solar cell power output. Qualitatively speaking, the results indicate that a very high quality substrate with a long recombination lifetime is needed to maintain the maximum power generation. The quantitative value of the recombination lifetime of minority-carriers, i.e., electrons in p-type substrates, required in the BCBJ cell is about one order of magnitude longer than that in the front-lit cell, i.e., 5 × 10−4 sec vs. 5 × 10−5 sec. Regardless of substrate thickness up to 150 μm, the power output in the BCBJ cell stays at nearly the maximum value of about 1.8 × 10−2 W·cm−2, or 18 mW·cm−2, as long as the recombination lifetime is 5 × 10−4 s or longer. The output power, however, declines steeply to as low as 10 mW·cm−2 when the recombination lifetime becomes significantly shorter than 5 × 10−4 sec. Substrate thinning is found to be not as effective as in the front-lit case in stemming the decline in the output power. In view of these results, for BCBJ applications, the substrate needs to be only mono-crystalline Si of very high quality. This bars the use of poly-crystalline Si, which is gaining wider acceptance in standard front-lit solar cells.

In photovoltaic power generation where minority carrier generation via light absorption is competing against minority carrier recombination, the substrate thickness and material quality are interdependent, and appropriate combination of the two variables is important in obtaining the maximum output power generation. Medici, a two-dimensional semiconductor device simulation tool, is used to investigate the interdependency in relation to the maximum power output in front-lit Si solar cells. Qualitatively, the results indicate that a high quality substrate must be thick and that a low quality substrate must be thin in order to achieve the maximum power generation in the respective materials. The dividing point is 70 μm/5 × 10−6 sec. That is, for materials with a minority carrier recombination lifetime longer than 5 × 10−6 sec, the substrate must be thicker than 70 μm, while for materials with a lifetime shorter than 5 × 10−6 sec, the substrate must be thinner than 70 μm. In substrate fabrication, the thinner the wafer, the lower the cost of material, but the higher the cost of wafer fabrication. Thus, the optimum thickness/lifetime combinations are defined in this study along with the substrate cost considerations as part of the factors to be considered in material selection.

Multi-source evaporation is one of the methods to improve the thickness uniformity of thin films deposited by evaporation. In this study, a simulator for the relative thickness profile of a thin film deposited by a multi-source evaporation system was developed. Using this simulator, the relative thickness profiles of the evaporated thin films were simulated under various conditions, such as the number and arrangements of sources and source-to-substrate distance. The optimum conditions, in which the thickness uniformity is minimized, and the corresponding efficiency, were obtained. The substrate was a 5th generation substrate (dimensions of 1300 mm × 1100 mm). The number of sources and source-to-substrate distance were varied from 1 to 6 and 0 to the length of the major axis of the substrate (1300 mm), respectively. When the source plane, the area on which sources can be located, is limited to the substrate dimension, the minimum thickness uniformity, obtained when the number of sources is 6, was 3.3%; the corresponding efficiency was 16.6%. When the dimension of the source plane is enlarged two times, the thickness uniformity is remarkably improved while the efficiency is decreased. The minimum thickness uniformity, obtained when the number of sources is 6, was 0.5%; the corresponding efficiency was decreased to 9.1%. The expansion of the source plane brings about not only the improvement of the thickness uniformity, but also a decrement of the efficiency and an enlargement of equipment.

글루탈알데히드와 황산을 이용하여 가교된 키토산 복합막을 제조하였다. 제조된 복합막은 글루탈알데히드와 황산용액을 이용하여 표면말을 선택적으로 가교하엿다. 제조된 키토산 막에서의 키토산과 아세트산간의 착체형성의 영향을 관찰하기 위하여 수산화나트륨으로 중화하여 성능을 비교하였다. 황산으로 표면을 가교한 경우 코팅된 활성층의 투과증발에 대한 영향을 관찰하였다. 글루탈알데히드로 가교된 키토산복합막은 지지체의 종류를 변화시키면서 투과증발성능을 비교하였다. 지지체의 순수투과성능이 증가할수록 투과유량은 비슷한 값들을 유지하였으며, 선택도는 증가하다가 다시 감소하는 경향을 나타내었다. 수산화나트륨으로 키토산을 중화시킨 경우에는 선택도는 감소하였고 투과유량은 유지되는 경향을 나타내었다. 황산을 이용하여 표면을 이온가교시킨 경우 키토산 복합막은 활성충우ㅏ 두께가 증가할수록 가교시간이 증가하여야 최적의 가교조건을 나타내었다.