Xueling Zhang

6 inch IBC cells with efficiency of 23.5% fabricated with low-cost industrial technologies

The rear contact pattern design of IBC cells plays an important role in achieving high cell efficiency. It necessitates a trade-off between a reduction of the internal recombination losses by using fine geometries of pitch and contact size, and a reduction of the series resistance losses by using large metal coverage and contact area ratio. In this paper, the rear contact pattern is optimized based on characterization and simulation techniques. From this optimization, IBC cells were fabricated on 6 inch pseudo-square n-type wafers with a champion cell demonstrating an efficiency of 23.5%, which is the highest total-area efficiency reported to date for a 6 inch IBC cell. Compared to our previous design, an absolute 0.5% efficiency gain has been achieved.

Independent Al2O3/SiNx:H and SiO2/SiN x:H Passivation of p+ and n+ Silicon Surfaces for High-Performance Interdigitated Back Contact Solar Cells

In order to improve interdigitated back contact (IBC) solar cell efficiencies, the entire solar cell surface must be well passivated. Al₂O₃/SiN_x:H and SiO₂/SiN_x:H passivation stacks have been widely adopted for high-efficiency silicon solar cells. We explored IBC solar cells with 1) only SiO₂/SiN_x:H; 2) only Al₂O₃/SiN_x:H passivating both diffused surfaces; or 3) independent p⁺ emitter and n⁺ back surface field (BSF) passivation with Al₂O₃/SiN_x:H and SiO₂/SiN_x:H respectively. First, stacks were optimized through simulation (using a device model in 3D Quokka) by varying the recombination parameter Jo. Second, solar cells were fabricated with a low-cost high-throughput screen-printing technique. Third, simulated J_sc, V_oc, F F , and η values closely matched the experimental results for passivation schemes 1 and 2. Passivation scheme 3 could not be realized experimentally due to fabrication difficulties, while its simulated values were 688 mV, 41.4 mA/cm², 80.8%, and 23.0%, respectively. It is clear that independent passivation captures material advantages for each diffused region for enhanced solar cell performance compared with conventional passivation of both diffused regions with a single passivation stack.

Balancing electrical and optical losses for efficient Si-perovskite 4-terminal solar cells with solution processed percolation electrodes.

The Cluster of Excellence funded this work through “Engineering of Advanced Materials” (EAM). The authors acknowledge financial support from the DFG research-training group GRK 1896 at Erlangen University and from the Joint Project Helmholtz-Institute Erlangen Nurnberg (HI-ERN) under project number DBF01253, respectively. The authors would like to acknowledge the company rent a scientist (RAS) for material support. C.J.B. acknowledges the financial support through the “Aufbruch Bayern” initiative of the state of Bavaria (EnCN and Solar Factory of the Future) and the “Solar Factory of the Future” with the Energy Campus Nurnberg (EnCN). C.O.R.Q would like to acknowledge Dr. Ning Li, Yi Hou, K. Ding, A. Richter, W. Duan and Andrej Classen for their support during the early stages of this project. Similarly C.O.R.Q would like to acknowledge Sara Mashhoun and Helena Waldau for her helpful advice and graphic design, respectively. A.H-B would like to thank C. Yi for his contributions in checking the electrical characteristics of the silicon solar cell. C.O.R.Q would like to gratefully acknowledge the financial support from The Mexican National Council for Science and Technology (CONACYT). This work was partly supported by the Australian Government through the Australian Renewable Energy Agency (ARENA).

Series resistance modeling of complex metallization geometries of solar cells using conductive line decomposition

All-back-contact (ABC), metal wrap through (MWT) and generally solar cell designs with complex metallization geometries are not amenable to simple series resistance (Rs) analysis based on small unit cells. In order to accurately determine the effects of Rs in these solar cells, SERIS developed a MATLAB program that captures the cell metallization geometry from rastered images, and breaks down the metalized areas into line segments of appropriate conductance. Its chief advantages over the conventional finite element method (FEM) solvers are: many-fold reduction in the number of mesh points used to define the metalized area and that the connections between elements are clearly defined, thus enabling approximations in the current flow pattern to speed up computation if desired. Its chief advantage over network/SPICE solvers is better adaptivity to complex metal geometries. The program solves for the terminal current-voltage characteristics, as well as the local current density, voltage and series resistance distributions, making it a versatile tool to aid the design of metal patterns.

Effect of carrier-induced hydrogenation on the passivation of the poly-Si/SiOx/c-Si interface

In the progress made in understanding carrier-induced degradation and regeneration in p-type mono and multi silicon solar cells, it was implied that hydrogen passivates certain defects during illuminated anneals at temperatures between 150-350°C. However, there are only few reports on the effect of carrier-induced regeneration (CIR) in n-type material. In this work, we apply a CIR treatment on samples structured as poly-silicon/tunnel oxide/n-type CZ. We present evidence suggesting that hydrogen passivation plays an important role in the regeneration process, and that improvement does not occur in the Si bulk but mainly at the Si/SiOx interface. For n-type poly, the Si/SiOx interface improves at temperatures of 250°C and above regardless of illumination and H-containing dielectric layer, and the rate of improvement is merely accelerated by illumination. For p-poly, the Si/SiOx interface is only stable in our experiments if the H-containing dielectric layer is present during CIR.

Correction: Balancing electrical and optical losses for efficient 4-terminal Si-perovskite solar cells with solution processed percolation electrodes

Correction for ‘Balancing electrical and optical losses for efficient 4-terminal Si-perovskite solar cells with solution processed percolation electrodes’ by Cesar Omar Ramirez Quiroz et al., J. Mater. Chem. A, 2018, 6, 3583–3592.