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Numerical analysis of dopant‐free asymmetric silicon heterostructure solar cell with SiO 2 as passivation layer
Author(s) -
Mehmood Haris,
Nasser Hisham,
Tauqeer Tauseef,
Turan Raşit
Publication year - 2020
Publication title -
international journal of energy research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.808
H-Index - 95
eISSN - 1099-114X
pISSN - 0363-907X
DOI - 10.1002/er.5720
Subject(s) - passivation , materials science , heterojunction , optoelectronics , dopant , band bending , silicon , solar cell , crystalline silicon , doping , band diagram , nanotechnology , layer (electronics)
Summary Conventional silicon heterojunction solar cells employ defects‐prone a‐Si:H layers for junction formation and passivation purposes. Substituting these layers with hole‐selective MoO x and electron‐selective TiO x can reduce parasitic absorption and energy band offsets issues associated with doped silicon films. In this work, dopant‐free asymmetric heterostructure Si solar cells are studied with and without SiO 2 passivation layer, and their performance has been compared. The inclusion of ultrathin SiO 2 insulator as a passivation layer promotes significant band bending that induces interface inversion of crystalline silicon as well as maintains the electric field required to tunnel charge carriers. The energy band diagram studies and variation of oxide thickness show that the IV characteristics of the solar cell critically depend on the insulator thickness; as the carriers tunnelling through the insulator becomes negligible at larger thicknesses. The simulated structure with MoO x as front hole‐selective contact and without any passivation exhibited conversion efficiency of 15.73%, which improved to 18.69% by incorporating passivated a‐Si:H. However, by employing rear SiO 2 /TiO x stack with the front SiO 2 /MoO x , the device performance enhanced to open‐circuit voltage of 785 mV, short‐circuit current density of 41 mA/cm 2 , fill factor of 77%, and simulated conversion efficiency of 24.83%, which is ∼10% enhancement in the performance as compared to reference device employing traditional a‐Si:H with dopant‐free films. Novelty Statement For the first time, a dopant‐free asymmetric silicon heterostructure solar cell (DASH) employing silicon oxide (SiO 2 ) as a passivation layer has been physically modelled using Silvaco TCAD. The dopant‐free MoO x and TiO x as hole‐ and electron‐selective contacts have been incorporated. An ultrathin SiO 2 promotes band bending that induces interface inversion of absorber as well as facilitating carrier tunnelling. An efficiency of 24.83% has been numerically attained which is the best performance among DASH structures designed with oxide passivation. The 2‐D cross‐section view of the proposed device employing dopant‐free layers and oxide passivated film is illustrated in Figure 1 for which we have applied memory intensive numerical method based on the computation of Poisson, charge transport and continuity equations in the Silvaco ATLAS module. In order to undertake in‐depth analysis of the proposed structure, a simple device based on MoO x /cSi wafer was first designed and simulated in order to understand the charge transport behaviour. The electrical and optical parameters for various layers have been shown in the Table and the current density due to tunnelling of charge carriers across Silicon oxide (SiO 2 ) passivated layer has been calculated via Fowler‐Nordheim approximation. The reference structure with traditional intrinsic a‐Si:H has also been simulated.