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 N 2 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 (J sc ) and open circuit voltage (V oc ). J sc and V oc have been increased from 0.010 mA/cm 2 up to 0.081 mA/cm 2 , 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 J sc and V oc , which is from 2.0 × 10 −4 % up to 5.2 × 10 −3 %.