Johannes Ziegler

Properties of black silicon obtained at room-temperature by different plasma modes

Black silicon plasma technology begins to be integrated into the process flow of silicon solar cells. However, most of the current technology is used at cryogenic or very low substrate temperatures. Here, the authors investigate the temperature-dependent properties of black silicon prepared by two different plasma etching techniques for black silicon, a pure capacitively coupled process (CCP), and an inductively and capacitively coupled process (ICP + CCP). It turns out that the ICP + CCP process at room-temperature yields black silicon samples with 93% absorption and minority carrier lifetime above 1 ms. The authors show that these optoelectronic properties are comparable to samples obtained at low temperatures.

Influence of black silicon surfaces on the performance of back-contacted back silicon heterojunction solar cells

The influence of different black silicon (b-Si) front side textures prepared by inductively coupled reactive ion etching (ICP-RIE) on the performance of back-contacted back silicon heterojunction (BCB-SHJ) solar cells is investigated in detail regarding their optical performance, black silicon surface passivation and internal quantum efficiency. Under optimized conditions the effective minority carrier lifetime measured on black silicon surfaces passivated with Al(2)O(3) can be higher than lifetimes measured for the SiO(2)/SiN(x) passivation stack used in the reference cells with standard KOH textures. However, to outperform the electrical current of silicon back-contact cells, the black silicon back-contact cell process needs to be optimized with aspect to chemical and thermal stability of the used dielectric layer combination on the cell.

Enhanced density of negative fixed charges in Al2O3 layers on Si through a subsequent deposition of TiO2

The passivation of silicon surfaces play an important role for achieving high-efficiency crystalline silicon solar cells. In this work, a stack system comprising of 20nm Al2O3 with a 22nm TiO2 topping layer was deposited on p-type Si using thermal atomic layer deposition (ALD) and was investigated regarding its passivation quality. Quasi-steady-state photo conductance (QSSPC) measurements reveal that the minority carrier lifetime at an injection density of 1015cm−3 increased from 1.10ms to 1.96ms after the deposition of TiO2, which shows that the deposition of TiO2 onto Al2O3 is capable of enhancing its passivation quality. Capacity voltage (CV) measurements show that the amount of negative charges in the dielectric layer has increased from -2.4·1012cm−2 to -6.3·1012cm−2 due to the deposition of TiO2. The location of the additional charges was analyzed in this work by etching the dielectric layer stack in several steps. After each step CV measurements were performed. It is found that the additional negative charges are created within the Al2O3 layer. Additionally, ToF-SIMS measurements were performed to check for diffusion processes within the Al2O3 layer.

Passivation of different black silicon surfaces by ALD deposited Al 2 O 3

Optical properties of black silicon (b-Si) can be tailored to minimize reflection losses to less than 0.6 % between 300-1000 nm and to improve the absorption at the silicon band-edge by light-trapping. Recently, metal assisted wet-chemically etched (MACE) b-Si was exploited to fabricate high efficiency (18.2 %) solar cells with surface passivation by thermal SiO2 and recombination velocities (SRV) of ~100 cm/s [1]. We compare surface passivation performance of ALD-Al2O3 on different dry and wet etched nanostructures. SRVs ≤ 8 cm/s on bifacially black 1 Ωcm p-type Si FZ wafers were measured. This technological advance will enable higher efficiencies for various PV-cell concepts.

Opto-electronic properties of different black silicon structures passivated by thermal ALD deposited Al 2 O 3

Black silicon (b-Si) structures offer improved light absorption but require appropiate surface passivation for photovoltaic applications. Here, we compare the opto-electronic performance of different wet and dry etched b-Si structures passivated by thermal ALD deposited Al2O3.

Passivation of optically black silicon wafers by atomic layer deposited Al2O3 films

Optically black silicon nanostructures show excellent light trapping properties. Towards the integration of these structures into a solar cell device, the passivation performance of atomic layer deposited thin Al2O3 films is investigated.