Ž . Journal of Non-Crystalline Solids 227–230 1998 1257–1261 Improvements in stability of amorphous silicon solar cells by using ECR-CVD processing Vikram L. Dalal a, ) , Tim Maxson b , Kay Han b , Sohail Haroon a a Department of Electrical and Computer Engineering, Iowa State UniÕersity, Ames, IA 50011, USA b Microelectronics Research Center, Iowa State UniÕersity, Ames, IA 50011, USA Abstract Ž . We report on significant improvements in the stability of a-Si:H prepared using an electron-cyclotron-resonance ECR plasma chemical vapor deposition process. The p-i-n samples were prepared on stainless steel substrates in a single ECR chamber reactor using a remote, diluted plasma process, with either hydrogen or helium being the diluent gas. The devices had fill factors of about 70%. The stability of the devices was monitored by subjecting the devices to 2 = sun illumination Ž . from a xenon lamp. We find that the devices prepared using the remote, hydrogen-diluted ECR H-ECR process had a stability with a degradation in fill factor of less than 5% over a 900-h illumination time. In contrast, the devices prepared using either He dilution, or with a standard glow-discharge process, were much less stable than the H-ECR devices. The stability of the H-ECR devices is directly related to the improved stability of the material produced using this technique. We have also fabricated tandem a-Sira-Si solar cells using this technique, and the stability of the tandem cells is also excellent. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Amorphous silicon; Hydrogen; Helium 1. Introduction The degradation in the performance of amorphous silicon solar cell devices under light soaking is a major technological problem. This degradation is directly related to the increase in defect density of the material upon light soaking, which leads to w x field-collapse in the device 1,2 and to a decrease in the hole diffusion length. In recent years, alternative deposition techniques, such as electron cyclotron Ž . resonance chemical vapor deposition ECR-DVD w x wx 3,4 , hot wire deposition 5 and hydrogen annealing wx 6 techniques have been employed to reduce the ) Corresponding author. Fax: q1 515 294 9584; e-mail: vdalal@iastate.edu. instability of the material, and thereby hopefully improve the stability of the cell. One of these tech- niques, a remote ECR-CVD deposition using hydro- gen dilution has been shown to improve the stability of p-i-n junction solar cells prepared using the super- wx strate geometry 7 . In this work, we follow those preliminary results by systematically exploring the stability of p-i-n junction solar cells deposited in the substrate geometry on stainless steel substrates. We show that the ECR process, particularly the use of hydrogen dilution in the remote mode, which we shall call the H-ECR process, is capable of produc- ing high quality cells with good stability. In contrast, we show that the use of non-reactive gases, such as helium, does not produce cells of equivalent stabil- ity. From this effect, we conclude that the chemistry 0022-3093r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. Ž . PII: S0022-3093 98 00251-8