Thin crystalline silicon solar cells based on epitaxial films grown at 165°C by RF-PECVD

Abstract

We report on heterojunction solar cells whose thin intrinsic crystalline absorber layer has been obtained by plasma enhanced chemical vapor deposition at 165°C on highly doped p-type (100) crystalline silicon substrates. We have studied the effect of the epitaxial intrinsic layer thickness in the range from 1 to 2.4 µm. This absorber is responsible for photo-generated current whereas highly doped wafer behave like electric contact, as confirmed by external quantum efficiency measurements and simulations. A best conversion efficiency of 7% is obtained for a 2.4 µm thick cell with an area of 4 cm 2 , without any light trapping features. Moreover, the achievement of a fill factor as high as 78.6% is a proof that excellent quality of the epitaxial layers can be produced at such low temperatures.

Low temperature plasma deposition of silicon thin films: From amorphous to crystalline

“…As a matter of fact, achieving epitaxial growth by hot-wire chemical vapor deposition has been demonstrated at low pressure (10 mTorr) in a wide range of temperatures (250 °C up to 770 °C) but the epitaxy breaks down for films thicker than 1 μm when the substrate temperature is below 550 °C, which has been explained by dehydrogenation of the growing surface as being the rate limiting step for epitaxial growth [16,20]. This is quite different from our results where epitaxial growth is maintained for films with thicknesses up to 4 μm [13] and moreover low hydrogen content is achieved in the epitaxial films (see Fig. 3) in spite of the low substrate temperature.…”

“…In the case of heterojunction solar cells, epitaxial growth has been shown to lead to poor surface passivation; therefore efforts have been done to avoid epitaxial growth [10,11]. However, one can take benefit of this to produce ultrathin crystalline silicon films which can be transferred to foreign substrates [12] as well as solar cells featuring such epitaxial films [13]. Besides their applied interest, they also raise questions about the growth mechanism of such epitaxial films at low temperature.…”

Feasibility of using thin crystalline silicon films epitaxially grown at 165 °C in solar cells: A computer simulation study

“…The area of the cells (2 × 2 cm 2 for the largest ones) was defined by sputtering ITO through a shadow mask and evaporating aluminium grid contacts above. More details are given in reference [5]. All interfaces are flat and no light-trapping schemes have been introduced.…”

“…In the wafer equivalent approach used by Cariou et al [5] the epitaxial silicon (epi-Si) films are deposited in a standard industrial radio frequency plasma enhanced chemical vapour deposition (RF-PECVD) system a e-mail: parsathi chatterjee@yahoo.co.in on highly doped c-Si (100) substrates at 165 • C, allowing for the additional advantage of a low thermal budget with a standard industrial tool. In these epi-Si films high crystalline quality and low stress levels have been confirmed from HRTEM and Raman measurements.…”

Direct Current Sputter Epitaxy of Heavily Doped p+ Layer for Monocrystalline Si Solar Cells

“…For further cost reduction of monocrystalline Si solar cells (SCs), both decreasing material usage by means of thin film and increasing power generation by increasing energy conversion efficiency are two effective methods. As for the approach by means of thin films, transferring of thin epitaxially grown Si film on Si wafer to foreign substrates is a promising method [1][2][3]. As for the latter approach, several structures of Si SC have been proposed and realized.…”