Improved coverage of rGO film on Si inverted pyramidal microstructures for enhancing the photovoltaic of rGO/Si heterojunction solar cell

Abstract

Solar cell fabricated by reduced graphene oxide (rGO)/textured silicon (T-Si) structure is feasible due to the capability to form a continuous film of graphene oxide (GO) on Si surface by direct drop-casting or spin coating. In this article, we have fabricated a uniform array of Si inverted pyramidal microstructures by anisotropic etching using a mixture of tetramethyl-ammonium hydroxide and isopropyl alcohol. Low average reflectance of 10.4% is obtained by T-Si structure as compared to that of 53.5% obtained by flat Si (F-Si) structure in UV–visible range. As a result, the front surface area of solar cell has been increased up to 43.2%. The dispersion of GO on Si surface textured with inverted pyramidal microstructures is performed by direct drop-casting of GO droplet or a combination of spin-coating and drop-casting on. The reduction of GO to form rGO is achieved by annealing in N2 at 400 °C. Direct drop-casting of GO droplet on T-Si results to the formation of suspended GO film, covering only the top of Si inverted pyramidal array. Due to the minimum contact area of rGO and T-Si after the reduction, higher diode ideality factor, η = 4.02 is obtained as compared to the reference rGO/F-Si diode with η = 3.99. A combination of spin-coating and drop-casting of GO droplet on T-Si helps in filling the GO sheets into the pyramidal structures, thus creating a large contact area with sidewalls of Si inverted pyramidal structures. As a result, the η value has been significantly reduced to 3.50. The power conversion efficiency also shows an increment due to the improvement of both short circuit current (Jsc) and open circuit voltage (Voc). Jsc and Voc have been increased from 0.010 mA/cm2 up to 0.081 mA/cm2, and from 96 mV up to 304 mV, respectively. Hence, the power conversion efficiency has been improved in several orders due to the improvement in both Jsc and Voc, which is from 2.0 × 10−4% up to 5.2 × 10−3%.