Page - 68 - in Photovoltaic Materials and Electronic Devices

a-Si:H; a plasmon feature in the Ag + ZnO interface; IR vibrational modes related to chemical bonding in a-Si:H and ZnO; and free carrier absorption in Ag and the Ag + ZnO interface have been obtained from spectra in ε. In addition to information on each of these materials in the n-i-p device structure, the structural and optical properties derived here can be applied in the future analysis of ex situ SE in either singlespot [36]ormappingconfigurations. 2. ExperimentalDetails Thin film doped and undoped Si:H films were deposited using a load-locked rf (13.56 MHz) PECVD reactor onto 6”ˆ6” borosilicate glass substrates coated with rf magnetronsputteredZnO/AgBRsasarecommonlyusedinn-i-pconfigurationsolar cells. Si:Hn-,p-, and i-layershavebeenpreparedusingdifferenthydrogendilution ratios, R, onto BR coated substrates or those otherwise mimicking the outermost previous layer in the device structure to generate growth evolution diagrams and identify the optimum conditions for protocrystalline a-Si:H for solar cells. Table 1 lists the deposition parameters used for fabrication of each layer including gas flows, pressure (p), power density (P), and substrate temperature (T). The deposition conditions used here were adopted from the Dahal et al., 2013 and Dahal et al., 2014 [23,37]. The deposition was done in the same chamber corresponding to reasonable device quality materials as evidenced by incorporation in n-i-p solar cells without textured BRs yielding ~7.5% efficiency. Maximum device performance parametersareopencircuitvoltageof0.90V,shortcircuit currentof12.5mA/cm2, and fill factor of 70%. The open circuit voltage and fill factor are reasonable for moderate quality n-i-p solar cells. The short circuit current is low as the specular BRdoesnotproducethe levelofscatteringexpectedfromatexturedBRwhere the optical path length of long wavelength light not initially absorbed in the intrinsic a-Si:H layer is increased. This increase in optical path length results in increased current density, which is absent for specular devices. The n-type Si:H films were deposited onto BR coated borosilicate glass. The intrinsic layers were deposited ontoBR’scoatedwithn-typea-Si:HpreparedatR=50. Thep-typeSi:Hfilmswere depositedontoborosilicateglass initiallycoatedwith~3000Åthick intrinsica-Si:H prepared at R=10. This intrinsic layer is deposited to eliminate any contributions to the microstructural evolution from the underlying glass substrate. Variable parameters were R = [H2]/[SiH4] for all three layers. The dopant gas ratios for n- (D= [PH3]/[SiH4]) and p-layers (D= [B2H6]/[SiH4]), whichcanhavesignificant influence on structural and the electronic properties, were fixed at D = 0.0125. Cr, Ag, and ZnO layers were prepared by rf magnetron sputtering at room temperature. Here, Cr was used as an adhesion interlayer to avoid delamination of the Ag film from the borosilicate glass. The ZnO/Ag BR structures were prepared under 68