Reliability Evaluation of Photovoltaic Modules Fabricated from Treated Solar Cells by Laser‐Enhanced Contact Optimization Process

Abstract

According to the International Technology Roadmap for Photovoltaics, passivated emitter and rear solar cells dominate the market in 2021 of up to 80% and are forecast to remain state of the art at least for the next 5 years. Within the production process of solar cells, it is typical to have cells with lower efficiency grades due to variations in manufacturing processes or material defects. Reprocessing such solar cells could save cost due to increased production yield and simultaneously reduced cost for recycling of unusable/unsellable low‐efficiency cells. Herein, the impact of the laser‐enhanced contact optimization (LECO) process on the power output and reliability of solar modules using commercial off‐spec cells of different manufacturers is analyzed. LECO is a downstream process for optimizing metal−semiconductor contacts on finished solar cells. The treatment leads to a significant economic gain due to enhanced cell efficiency (Wp ↑, therefore manufacturing cost per Wp ↓) even of already good solar cells. Herein, the first evaluation of the impact of the LECO process on the cell output power on an industrial scale (>1000 cells) and on module reliability is presented. The results for common short‐term effects like light‐induced degradation and light‐ and elevated temperature‐induced degradation are within expected limits and the durability against, for example, potential‐induced degradation is not changed due to the LECO process. The results further show that cell sorting is crucial for a reliable module and to avoid outliers in terms of unexpected degradation and recovery phenomena of individual cells.

Laser‐enhanced contact optimization on iTOPCon solar cells

“…However, for practical reasons, accelerated testing on cell level is chosen. Furthermore, the in‐depth module aging tests conducted on LECO‐enhanced PERC modules 24 and the presented data for i TOPCon solar cells in this work significantly raise confidence on the stability of LECO‐improved solar cells in terms of contact resistivity and LeTID in general.…”

“…However, for practical reasons, accelerated testing on cell level is chosen. Furthermore, the in-depth module aging tests conducted on LECO-enhanced PERC modules24 and the presented data for iTOPCon solar cells in this work significantly raise F I G U R E 3 Contact resistivity ρ c of the emitter as well as on the tunnel oxide passivated contact (TOPCon) side with a thickness of 170 nm prior and after laser-enhanced contact optimization (LECO), measured using a TLM-SCAN + unit from PV tools. Each box plot corresponds to at least 50 data points measured equally distributed throughout one solar cell.…”

“…Obviously, it is important that the enhanced state is stable over time. Standard module aging tests such as thermo cycling TC, damp heat DH, and potential induced degradation PID published by Krassowski et al 24 on LECO‐treated PERC devices show no significant difference to untreated reference modules. Also, the effect of light and elevated temperature‐induced degradation (LeTID) 25 was not observed in those tests.…”

“…The measurements are conducted in an industrial cell tester, calibrated with a Fraunhofer ISE CalLab measured cell against a non-reflecting, locally contacting chuck. The cell tester uses a PCB-touch unit from Pasan with 30 current wires/traces for front and rear respectively such as thermo cycling TC, damp heat DH, and potential induced degradation PID published by Krassowski et al24 on LECO-treated PERC devices show no significant difference to untreated reference modules. Also, the effect of light and elevated temperature-induced degradation (LeTID)25 was not observed in those tests.In our study, LECO treated iTOPCon solar cells are submitted to elevated temperatures at 140 C and simultaneously kept at constant irradiation of 2000 W/m 2 (2 suns) equivalent.…”

Short Drying Processes for Silicon Solar Cells

“…[23] The power conversion efficiency is taken as a measure for the overall solar cell performance. After the initial I-V measurements, the solar cells are treated with the LECO process [24][25][26][27][28] and I-V measured again. LECO is a relatively new process that improves underfired silver-silicon contacts to the optimum stage and is, therefore, more and more used in the PV community.…”