Development of p-i-n Heterojunction Quantum Dot (QD) Solar Cells
- Category: Energy, Materials, Nanotechnology
- Tags: dong-kyun ko, vladimir bulovic
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Download as PDFDisordered semiconductors exhibit poor electronic transport properties due to their amorphous nature. Low carrier mobility and lifetime limits the diffusion length to 100 ~ 300 nm. Thus, conventional p-n junction photovoltaic design that is composed of a large quasi-neutral region and a small depletion region (Figure 1a) leads to poor charge extraction. To overcome this material limit, a p-i-n junction has been adopted in amorphous silicon solar cells. The internal electric field extends throughout the intrinsic absorber layer and assists carriers to be efficiently extracted to their respective electrodes (Figure 1b). Films composed of quantum dots (QD) show electronic transport properties similar to disordered semiconductors and may also benefit from the p-i-n “drift” device architecture, which has not been applied to QD solar cells to date.
This project aims to implement two major advantages of the p-i-n heterojunction using the QD as an intrinsic absorber layer. The first goal is to augment the width of the depletion region. This widening enhances the light absorbance of the device, allowing more photogenerated carriers and thereby increasing short-circuit current (Jsc). The second advantage to exploit is the ability to dope n- and p-type layers without having to affect the intrinsic absorber layer. Increasing the Fermi level difference by doping both window layers would increase the build-in electric field, enhancing open-circuit voltage (Voc). Figure 1c and d show schematic illustrations of the device structure and energy diagram, respectively. Figure 2a and b show the device characteristic studied for each separate junction. Rectifying behavior is observed in both p-i, i-n and p-i-n junctions. Figure 2d and e show the JV curve under illumination with and without the intrinsic QD absorber layer. Future studies will focus on Voc, Jsc, and fill factor (FF) as a function of p-type and n-type layer doping as well as intrinsic layer thickness.
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- Figure 1: Schematic illustration of (a) crystalline and (b) amorphous silicon solar cell devices (adopted from reference [1]). QD p-i-n solar cell (c) device structure and (d) energy diagram.
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- Figure 2: Dark JV characteristics of (a) p-i, (b) i-n, and (c) p-i-n junctions. Dark and light JV curve of (d) p-n and p-i-n junctions.
- M. Zeman, “Solar Cells,” TU Delft OpenCourseWare, Delft University of Technology, 2011. [Online]. Available: http://ocw.tudelft.nl/courses/microelectronics/solar-cells/readings/