Highly and Rapidly Stabilized Protocrystalline Silicon Multilayer Solar Cells

Abstract

We have developed highly stabilized (p-i-n)-type protocrystalline silicon (pc-Si:H) multilayer solar cells. However, the source of the superior light-induced stability of the pc-Si:H multilayer absorbers compared to conventional amorphous silicon (a-Si:H) absorbers remains unclear. Photoluminescence (PL) and Fourier transform infrared (FTIR) spectroscopy measured at room temperature produce strong evidence that nano-sized silicon grains embedded in regularly arranged highly H 2 -diluted sublayers suppress the photocreation of dangling bonds. To achieve a high conversion efficiency, we applied a double-layer p-type amorphous siliconcarbon alloy (p-a-Si 1-x C x :H) structure to the pc-Si:H multilayer solar cells. The less pronounced initial short wavelength quantum efficiency variation as a function of bias voltage, and the wide overlap of dark current -voltage (J D -V) and short-circuit current -open-circuit voltage (J sc -V oc ) characteristics prove that the double p-a-Si 1-x C x :H layer structure successfully reduces recombination at the p/i interface. Thus, we achieved a highly stabilized efficiency of 9.0 % without any back reflector.

Characterization of the protocrystalline silicon multilayer

“…However, a new peak centered at $2090 cm À1 was found for the pc-Si:H multilayer. In our previous report [6,7], we attributed the peak to an inclusion of small crystalline-like objects (CLO) in S H . We decomposed the stretching band in the wave number region of 1900-2200 cm À1 into two Gaussian peaks.…”

“…This peculiar structure can be ascribed to the repetition of S L and S H . In our previous works based on the photoluminescence (PL) and FTIR measurements at room temperature, we expected the existence of the embedded CLO in well-ordered a-Si:H matrix of S H [6,7]. Recently, we have presented 3-5 nm sized spherical CLO embedded in a-Si:H matrix from high resolution TEM (HRTEM) images [9].…”

Deposition phase diagrams for Si1−xGex:H from real time spectroscopic ellipsometry

“…Optimization of the a-Si:H i-layer component of the top cell has been widely successful by applying the concept of maximum H 2 dilution [3]. This concept has been applied in both two-step [4] and multistep [5] processing in order to achieve the greatest benefits of atomic H, while suppressing microcrystallite evolution. Potential benefits include enhanced precursor surface diffusion in the PECVD process, as well as sub-surface strained bond relaxation [6].…”

Photoresponse and carrier transport of protocrystalline silicon multilayer films

“…The hydrogenated amorphous silicon (a-Si:H) solar cell has become one of the main structures of industrial silicon-based thin-film solar cells because of its low-cost, light weight and low-temperature deposition [1]. However, lightinduced degradation, an intrinsic characteristic of these materials, has greatly limited their practical application in novel photovoltaic technology [2].…”

“…The carriers transport mechanism in pc-Si:H films is complex, as it is a composite material made up of a nanocrystalline phase, a grain boundary and an amorphous phase. For photovoltaic applications, it is believed that the larger cross-section of the favored carrier traps of isolated silicon NCs than those of the defects, reduces the nonradiative recombination of photo-generated carriers in the amorphous silicon matrix [1], which helps to improve the photoresponse and suppress light-induced degradation. However, increased carrier traps in the defects [9] and carrier recombination within silicon NCs with increased proportions of silicon NCs will significantly affect the photovoltaic properties of pc-Si:H films.…”