Modeling the potential of screen printed front junction CZ silicon solar cell with tunnel oxide passivated back contact

Abstract

Carrier selective passivated contacts composed of thin oxide, n + polycrystalline Si and metal on top of a n-Si absorber can significantly lower the recombination current density (J orear ≤8 fA/cm 2 ) under the contact while providing excellent specific contact resistance (5-10 mΩ-cm 2 ); 25.1% efficient small area cells with photolithography front contacts on boron doped selective emitter and Fz wafers have been achieved by Fraunhofer ISE using their tunnel oxide passivated contact (TOPCon) approach. This paper shows a methodology to model such passivated contact cells using Sentaurus device model, which involves replacing the TOPCon region by carrier selective electron and hole recombination velocities to match the measured J orear of the TOPCon region as well as all the light IV values of the cell. We first validated the methodology by modeling a 24.9% reference cell. The model was then extended to assess the efficiency potential of large area TOPCon cells on commercial grade n-type Cz material with screen-printed front contacts. To use realistic input parameters, a 21% n-type PERT cell was fabricated on Cz wafer (5 Ω-cm, 1.5-ms lifetime). Modeling showed that the cell efficiency will improve to only 21.6% if the back of this cell is replaced by the above TOPCon, and the performance is limited by the homogenous emitter. Efficiency was then modeled to improve to 22.6% with the implementation of selective emitter (150/20 Ω/sq). Finally, it is shown that screen printing of 40-μm-wide lines and improved bulk material (10 Ω-cm, 3-ms lifetime) can raise the single side TOPCon Cz cell efficiency to 23.2%.

Review of Laser Doping and its Applications in Silicon Solar Cells

“…There is a significant discrepancy in the J 0 associated with front and rear surface, with the efficiency of the cell being limited by the front surface design. A selective emitter design would appear a sensible step to drive performance enhancements in TOPCon, with modelling suggesting an efficiency gain of 1% abs being possible [76].…”

Application of n‐Polysilicon Rear Emitter for High‐Efficiency p‐TOPCon Solar Cells

“…[18,5,6] In the laboratory, the efficiencies of the champion solar cell with polysilicon-based passivated contact have been increased to 25.7% (front and rear contact) [22,23] by Fraunhofer ISE and 26.0% [24] by ISFH/Hannover University. Moreover, theoretical simulation studies further provide equitable insight into a silicon solar cell with a polysiliconbased passivated contact, comprising the selective collection of charge carriers, [25,26] surface passivation, [27,28] pinhole-assisted transportation, [29,30] screen printing, [27] wafer parameters, [31,22,23] and impurity contamination. [32] Typically, silicon solar cells based on passivated contacts with polysilicon have emerged as competing contenders for high conversion efficiency owing to their easy construction and superior performance.…”

Application of Phosphorus‐Doped Polysilicon‐Based Full‐Area Passivating Contact on the Front Textured Surface of p‐Type Silicon

“…This classification standard has been demonstrated by modeling a reference cell with TOPCon stack from Fraunhofer Institute, which was then extended to assess the efficiency potential of large area TOPCon cells on commercial grade Cz Si material with screen‐printed contacts. [ 40 ] Taking advantage of the technology available including the increase in surface concentration and junction depth of emitter doping, constriction of front finger width, and improvement of paste composition as well as sintering has the capacity to keep the electrode forming good ohmic contact. [ 41 ] The J 0e.metal value was expected to decrease from 100 to 5 fA cm −2 , resulting in an absolute increase in cell efficiency of 0.4% to 21.7%.…”

“…SiO 2 layer can be further optimized such as reducing the density of interface state, adjusting oxygen content to increase the energy gap, and optimizing the film thickness and compactness to enhance the field effect and chemical passivation. [ 18,40 ] Improvement of cell efficiency to 22.2% is calculated due to the decrease of J 0e.pass from 75 to 8 fA cm −2 . Furthermore, using local boron doping, better back electrode paste, less front electrode shading, and better substrate material such as increase in resistivity and bulk lifetime, [ 40 ] the optimized solar cell can be realized with the efficiency increased to 23.4% based on the decrease of J 0.total from 118 to 33 fA cm −2 .…”

“…[ 18,40 ] Improvement of cell efficiency to 22.2% is calculated due to the decrease of J 0e.pass from 75 to 8 fA cm −2 . Furthermore, using local boron doping, better back electrode paste, less front electrode shading, and better substrate material such as increase in resistivity and bulk lifetime, [ 40 ] the optimized solar cell can be realized with the efficiency increased to 23.4% based on the decrease of J 0.total from 118 to 33 fA cm −2 . From the listed solar cell electrical parameters in Figure 5c, the enhancement in cell efficiency is mainly profited from the improved V OC .…”