Problems of efficiency of photoelectric conversion in thin-film CdS/CdTe solar cells
- PDF / 338,672 Bytes
- 18 Pages / 612 x 792 pts (letter) Page_size
- 37 Downloads / 185 Views
ICS OF SEMICONDUCTOR DEVICES
Problems of Efficiency of Photoelectric Conversion in Thin-Film CdS/CdTe Solar Cells L. A. Kosyachenko^ Chernovtsy National University, Chernovtsy, 58012 Ukraine ^e-mail: [email protected] Submitted September 19, 2005; accepted for publication November 7, 2005
Abstract—The available data are generalized and new results of investigation of losses of photoelectric energy conversion in CdS/CdTe thin-film solar cells are reported. The requirements concerning the electrical characteristics of the material, for minimizing the electric losses and providing effective radiation absorption in the active region of the diode structure, are discussed and refined. It is shown to what extent the incomplete collection of photogenerated charge carriers is determined by recombination both at the CdS/CdTe interface (based on the continuity equation taking into account the surface recombination) and in the space-charge region (based on the Hecht equation). The comparison of the calculated and experimental results shows that, in general, both types of recombination losses are important but can be virtually eliminated by the choice of parameters of both the barrier structure and the material used. The limiting values of the short-circuit current density and efficiency of the CdS/CdTe solar cell are discussed. PACS numbers: 84.60.Jt DOI: 10.1134/S1063782606060182
1. INTRODUCTION It was shown that the CdS/CdTe heterojunction is promising for use in solar cells already in early studies devoted to this problem [1, 2]. The efficiency of the first solar cells obtained by vacuum deposition of CdS on the CdTe single-crystal substrates was 7–8% [2, 3]. The lattice mismatch between CdS and CdTe is large (~10%). However, its adverse effect is lowered to a great extent in the heterostructure with the CdTexS1 – x transition graded-gap layer (x = 0–1), which is fabricated by the solid-phase substitution of Te for S during isothermal annealing of the CdS single crystals in the Te vapor or by the thermal treatment of the as-prepared CdS/CdTe structure [4, 5]. The possibility of realizing the CdS/CdTe thin-film heterostructure in inexpensive and rather efficient large-area solar cells and, consequently, the possibility of their large-scale production in the future was demonstrated in the 1990s. Samples of area ~1 cm2 were obtained by chemical deposition of CdS on glass substrates coated with an ITO or SnO2 conducting transparent layer followed by sublimation of CdTe in a closed volume. The efficiency of these samples was increased to 15.8% [6]. Under the conditions of solar radiation (AM1.5), a record value of the short-circuit current density 26.7 mA/cm2 was attained [7]. Researchers succeeded in applying the extremely inexpensive technology of fabrication of the CdS/CdTe thin-film heterostructure for batteries of area 27 × 60 and 82 × 71 cm2, power 45 and 140 W, and efficiency 10.5 and 8.4% [8]. The results obtained for small-area
cells demonstrates prospects for increasing the efficiency of such batteries to at leas
Data Loading...
