Case study of failure analysis in thin ﬁlm silicon solar cell D. Mello a, ⁎, R. Ricciari a , A. Battaglia b , M. Foti a , C. Gerardi a a STMicroelectronics, Stradale Primosole 50, 95121 Catania, Italy b 3Sun, Contrada blocco torrazze 95100 Catana, Italy abstract article info Article history: Received 25 May 2015 Received in revised form 20 June 2015 Accepted 21 June 2015 Available online xxxx Thin-ﬁlm silicon modules are commonly produced by an alternating sequence of layer deposition and layer pat- terning steps, which lead to a monolithic series connected device. Most used process is laser scribing process that offers a high throughput and a small area loss. Tin oxide (SnO 2 ) or zinc oxide (ZnO) are the most used front con- tact TCO in the superstrate conﬁguration. ZnO presents better optical properties with respect to SnO 2 and can be realized by low thermal and cost effective deposition processes. Electrical performance of our tandem thin ﬁlm silicon cell deposited on ZnO front contact has shown higher shunt with respect with our reference process using SnO 2 front contact, not explained only as difference between the two materials. In this work, a failure anal- ysis process was followed in order to explain the origin of the difference. SEM, FIB and Auger electron spectros- copy were used in order to characterize the laser scribe that is known to be a possible cause of electrical deviation. We found residuals either on the bottom either on the later wall of P3 scribe that can explain the lowering shunt resistance and open circuit voltage observed into the electrical performances of the module. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Large area thin-ﬁlm silicon panels are widely diffused in the market of photovoltaic modules. They are commonly realized by an alternating sequence of layer deposition and layer patterning steps, which leads to a monolithic series connected device (Fig. 1). Most used process is laser scribing patterning that offers a high throughput and a small area loss. The process allows a cost effective manufacturing process and is suitable for application on large area low cost substrates such as glass, plastics and metals. Large areas (N 1m 2 ) can be processed because (a) TF deposition fa- cilities are usually scalable, and (b) the individual PV cells of a large module can be serially interconnected without the need of time- consuming wiring. To achieve this task, three patterns (P1, P2, P3) are realized during fabrication by laser scribing. In this respect, lasers have become key-components in the production of TF PV modules. In the superstrate conﬁguration, the substrate is transparent and fac- ing the incoming sunlight. The ﬁrst deposited layer is a Transparent Con- ductive Oxide (TCO), followed by an absorber layer, and a back contact/ reﬂector. Tin oxide (SnO 2 ) or zinc oxide (ZnO) is the most used front contact (TCO) in the superstrate conﬁguration. ZnO shows better optical prop- erties with respect to SnO 2 , such as higher transmittance and more con- trolled high haze, leading in higher cell current. Moreover, ZnO can be realized by low thermal and cost effective deposition processes (ZnO:Al by sputtering, ZnO:B by MOCVD). Electrical performance of our tandem thin ﬁlm silicon cell deposited on ZnO front contact has shown higher shunt with respect to our refer- ence process using SnO 2 front contact, not explained only as difference between the two materials. In this work, a failure analysis process was followed in order to ex- plain the origin of the difference. Scanning electron microscopy (SEM), focused ion beam (FIB) and Auger electron spectroscopy were used in order to characterize the laser scribe that is known to be a pos- sible cause of electrical deviation [1]. 2. Experimental We have studied tandem (a-Si/μc-Si) thin silicon module fabricated in superstrate conﬁguration on glass with SnO 2 or ZnO front contact TCO. SEM cross sections were performed with a FIB dual beam (DB) FEI DA300 equipped with a Sirion electron column, a Magnum ion column and with a gas injector system used for in situ contrast layer deposition. Auger analyses were performed using PHI Smart 200 equipped with Ar + ion gun for surface cleaning and depth proﬁling analysis. 3. Result and discussion The electrical performance of tandem thin ﬁlm silicon cell deposited on ZnO:B front contact, compared with our reference process using SnO 2 front contact, is affected by a lower open circuit voltage (Voc) and worst shunt resistance (R sh ). I–V curves of modules are reported in Fig. 2. The difference with respect to the case of SnO 2 cannot be explained only as effect of the work function difference between the two materials. Microelectronics Reliability xxx (2015) xxx–xxx ⁎ Corresponding author. E-mail address: domenico.mello@st.com (D. Mello). MR-11589; No of Pages 4 http://dx.doi.org/10.1016/j.microrel.2015.06.040 0026-2714/© 2015 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Microelectronics Reliability journal homepage: www.elsevier.com/locate/mr Please cite this article as: D. Mello, et al., Case study of failure analysis in thin ﬁlm silicon solar cell, Microelectronics Reliability (2015), http:// dx.doi.org/10.1016/j.microrel.2015.06.040