Griddler 2.5: Full Area Bifacial Cell Design and Simulation for the Bifi PV Community

Transcription

1 Griddler 2.5: Full Area Bifacial Cell Design and Simulation for the Bifi PV Community BiPV Workshop September 30, 2016 Miyazaki, Japan Johnson Wong (presented by Yong Sheng Khoo) Solar Energy Research Institute of Singapore, National University of Singapore, Singapore , Singapore 1

2 Introduction In developing a solar cell, continuous improvement, or evaluation of a new process or material, it is important to not only monitor changes in cell I-V characteristics, but also the various contributors to the I-V parameters For cell voltage (related to V oc and FF), one needs to quantify where the recombination currents are occurring (wafer passivated regions? wafer periphery and edges? Under the metal contacts?) and how much of an impact these recombination currents make on the V oc and FF. We present a neat example in a set of n-type bifacial solar cell and midstream samples from Shanghai Shenzhou New Energy Development Co. Ltd* This presentation will also focus on Griddler 2.5, the finite element program used in this work. *presented at IEEE PVSC, Portland, USA June

3 Griddler 2.5 an easy to use finite element program It takes only 5 minutes to.. 1. Design front and rear grids 2. Automatic meshing 3. Bifacial cell simulation. 3

4 Griddler Simulation Model of a bifacial cell Front side: Dual print 4BB, segments of 1 mm and 0.2 mm width 90 fingers, width 42 um Rear side: Single print 4BB, segments of 1 mm and 0.2 mm width 120 fingers, width 58 um 4

5 Griddler Simulation Model of a bifacial cell Front side: Dual print 4BB, segments of 1 mm and 0.2 mm width 90 fingers, width 42 um Rear side: Single print 4BB, segments of 1 mm and 0.2 mm width 120 fingers, width 58 um 5

6 Simulation Experiment PL Images of midstream and cells (and best fit) front dielectric p + Finished Cell 3 Metal grid (contact fired) front dielectric p + Cell with only rear grid 3 front dielectric p + Cell with only front grid 1 Metal grid (contact fired) front dielectric p + Cell with no grid 1 n-type base p-type mono wafer n-type base p-type mono wafer n-type base p-type mono wafer n-type base p-type mono wafer n + rear dielectric n + rear dielectric n + rear dielectric n + rear dielectric Metal grid (contact fired) Metal grid (contact fired) 6

7 Extracted saturated recombination current Chart Title densities Emitter J 0e is comparable to a good phosphorus emitter; with dual print the impact of front metal recombination is phosphorus metal low contact, 58 BSF is quite opaque electronically (rear contact induced recombination is boron metal negligible); lighter diffusion will reduce contact, 61 passivated rear J 0 Peripheral recombination is significant Griddler 2 Fitting Best Fit Value Parameter Wafer J fa/cm 2 Wafer J 02 6 na/cm 2 Front metal induced J fa/cm 2 Front metal induced J 02 0 na/cm 2 Rear metal induced J fa/cm 2 Rear metal induced J 02 0 na/cm 2 Peripheral J fa/cm 2 within a 2mm rim of the wafer edge One sun open circuit recombination currents (fa/cm 2 ) peripheral and edge recombination, 155 2nd diode, 15 *J Wong et al, IEEE JOURNAL OF PHOTOVOLTAICS, VOL. 5, NO. 2, MARCH passivated emitter, 89 passivated bulk and rear, 182 7

8 Fill Factor (%) How does the cell arrive at 80.7% FF? ideal FF at 650mV Apparent J 02 related losses Resistive losses (determined from other measurements, e.g. TLM for contacts) cell FF 0 emitter 2resistance 4 Axis current Title 6 sink at 8 busbars10 p finger resistance p busbar resistance p contact resistance n finger BSF resistance Injection dep lifetime and depletion region recombination Peripheral recombination 8

9 Rooms for Improvement By running different scenarios in Griddler using altered parameters: J sc (ma/cm2) V oc (mv) FF (%) Eff (%) Present Eliminate front metal induced recombination Eliminate rear metal induced recombination Turn off peripheral recombination

10 Conclusions: By preparing cells with absence of front or rear grids, and fitting Griddler simulated luminescence images to experimental images of these samples, one can extract the metal induced recombinations as well as the wafer edge and peripheral recombination parameters. One can easily define the front and rear grids in Griddler 2.5. For complicated designs, Griddler 2.5 can export/import from AUTOCAD. I-V curve simulation is a standard feature, allowing one to study the impact of parameter change (e.g. finger number, edge recombination) on the cell performance. One can also simulate different scenarios to gauge the headroom for improvement. Future Work: Griddler Automata, a routine to auto-fit to luminescence images and other data to assemble a Griddler model with minimal human intervention. 10

11 Thank You! Download Griddler tonight! 11

12 Efficiency (%) Further Efficiency Improvement Scenarios Modelled efficiency improvement implementing improvements or process changes (note: the below graph is for a different bifacial cell model than previous slides) Phosphorus BSF optimization Reduce rear recombination J 0 to 47fA/cm 2 multiwire Raise Jsc inbetween fingers to 42mA/cm measured 2 Boron 4Process 6 8 cell emitter Axis uniformity Title efficiency optimization improvement 12