Efficient silicon nitride SiNx:H antireflective and passivation layers deposited by atmospheric pressure PECVD for silicon solar cells

This work demonstrates the efficient optical and passivation properties provided by hydrogenated silicon nitride (SiNx:H) layers deposited in a lab-scale atmospheric pressure plasma enhanced chemical vapor deposition (AP-PECVD) reactor. By applying modulated low-frequency plasma (200 kHz), homogeneous SiNx:H layers, with small variances in thickness w and refractive index n (Delta w <= 2 nm; Delta n <= 0.02), were achieved on a surface area of 45 x 55 mm(2). The use of voltage amplitude modulation enabled discharge optimization and led to greatly enhanced SiNx:H film homogeneity and conformity in comparison with continuous plasma discharge conditions. Additionally, AP-PECVD SiNx:H showed good thermal stability (Delta w <= 1 nm; Delta n <= -0.02) with low absorption coefficients (k <= 0.1 at 275 nm), demonstrating that such layers could act as efficient antireflective coatings. Furthermore, outstanding surface passivation properties were achieved after firing, both on n-type FZ c-Si substrates of standard 2.8 omega.cm doping (tau(eff) = 1.45 ms) and on highly doped 85 omega/sq n(+) emitters (j(0e) = 74 +/- 2 fA.cm(-2)). Finally, AP-PECVD SiNx:H thin films were tested on industrial passivated emitter and rear solar cell (PERC) architectures, where the potential of applying these layers both as efficient rear-side capping layer and front-side antireflective coating was demonstrated. The first lab-scale 40 x 40 mm(2) PERC solar cells featuring AP-PECVD SiNx:H layers led to conversion efficiencies of up to 20.6%. These results pave the way for upscaling the dielectric barrier discharge lab-scale reactor in an industrial in-line process, which could provide low-cost and high-throughput SiNx:H capping and antireflective layers.