| AVS 60th International Symposium and Exhibition | |
| Energy Frontiers Focus Topic | Monday Sessions |
| Session EN+PS+TF-MoM |
| Session: | Thin Film, Organic, and Chalcogenide Solar Cells |
| Presenter: | C. Sentman, Colorado School of Mines |
| Authors: | C. Sentman, Colorado School of Mines M. O'Brien, Trinity College Dublin, Ireland C.A. Wolden, Colorado School of Mines |
| Correspondent: | Click to Email |
Pyrite, FeS2, is a non-toxic, earth abundant semiconductor that offers several potential advantages as a photovoltaic material, including low cost, large absorption coefficients and a band gap that is suitable for the harnessing of solar energy. Conventional thin film deposition techniques typically require the use of a post-deposition annealing step in elemental sulfur in order to achieve stoichiometric material. This cumbersome step is usually conducted in sealed quartz ampoule, requiring precise control over sulfur mass, time, and temperature. In this talk we introduce pulsed plasma-enhanced chemical vapor deposition (PECVD) as an alternative technique for thin film pyrite synthesis. In pulsed PECVD a mixture of iron pentacarbonyl (IPC, Fe(CO)5) diluted in H2S is delivered continuously to the reactor while the plasma is pulsed using square wave modulation at low frequency (~1 Hz). The concept is that IPC absorbs during the plasma off step, and that it is fully sulfurized in situ during the plasma on step. The process offers digital control over thickness with control on the order of ~1 Å/pulse. In this work we demonstrate the conditions required to achieve self-limiting growth of pyrite thin films. The dependence of pyrite deposition rate and material quality as a function of relevant variables such as H2S:IPC ratio, plasma duty cycle, plasma power, pressure and substrate temperature is described. Films are characterized using a suite of analytical techniques including Raman, XRD, FESEM, and UV-Vis-NIR spectrophotometry. Through appropriate control of deposition parameters stoichiometric FeS2 could be deposited at controllable rates between 0.1 – 1 Å/pulse without the need for post-deposition annealing. The onset of thermal CVD between these precursors was found to be ~300 ºC, and it is shown that this process leads to the formation of undesirable sulfur-deficient phases. Processing could also be used to tune the pyrite to marcasite ratio. Films display expected absorption coefficient (~105 cm-1) and optical band gap (~1 eV). We are currently analyzing their optoelectronic properties and will report on the process-structure-property relationships in this system.