Potential of Photocurrent Improvement in µc-Si:H Solar Cells using ZnO:B coated Substrates Structured by Direct Laser Interference Patterning

TARETTO, KURT; BERGER, JANA; SOLDERA, MARCOS M.; LASAGNI, ANDRÉS F.

Darmstadt

Conferencia; Materials Science and Engineering; 2018

DGM

Thin film solar cells based on weak absorbers like hydrogenated microcrystalline silicon (µc Si:H) need an effective light management to maximize light absorption inside the photoactive material [1]. One route to optimize light absorption is using the transparent front electrode of the solar cell as a diffraction grating to split the incoming sunlight into multiple propagation modes [2]. We propose using diffraction gratings fabricated with direct laser interference patterning (DLIP) on boron doped zinc oxide (ZnO:B) coated substrates, which results in periodical sinusoidal grooves with periods between 0.8 µm and 5 µm [3]. To estimate the photocurrent improvement with the patterned substrates we solve Maxwell?s equations rigorously using the finite element method in state-of-the-art µc Si:H solar cells [4]. The geometric parameters of the simulated patterns, namely the period and structure depth, are taken from confocal optical microscopy measurements of DLIP processed samples with sine-like grooves. Our results suggest that this laser technology is suitable to enhance the photocurrent of thin film µc Si:H solar cells deposited on ZnO:B. The highest photocurrent enhancements relative to the flat solar cell are obtained for texture periods between 0.8 µm and 1.5 µm due to the diffraction of incoming light into the first and second order propagation modes. In the case of a 2 µm thick silicon solar cell, the photocurrent enhancement lays in the range 15-35% for periods between 0.8 µm and 1.5 µm and texture heights between 100 nm and 200 nm. The optimized patterned device with 2 µm thick silicon layer yielded a photocurrent of 20.8 mA/cm2, which is the same photocurrent delivered by a flat solar cell with a 5 µm silicon layer. This implies a potential silicon thickness reduction of at least a factor 2 to obtain the same device efficiency as the flat solar cell upon using DLIP.References[1]A. Poruba, A. Fejfar, Z. Reme?, J. ?pringer, M. Vaněček, J. Kočka, J. Meier, P. Torres, A. Shah, J. Appl. Phys. 2000, 88, 148.[2]R. Dewan, D. Knipp, Journal of Applied Physics 2009, 106, 074901.[3]J. Berger, T. Roch, S. Correia, J. Eberhardt, A.F. Lasagni, Thin Solid Films 2016, 612, 342.[4]M. Soldera, K. Taretto, J. Berger, A.F. Lasagni, Adv. Eng. Mater. 2016, 18, 1674.