Carrier transport mechanism in the SnO2:F/p-type a-Si:H heterojunction

Abstract

We characterize SnO 2 :F/p-type a-Si:H/Mo structures by current-voltage (I-V) and capacitance-voltage (C-V) measurements at different temperatures to determine the transport mechanism in the SnO 2 :F/ p-type a-Si:H heterojunction. The experimental I-V curves of these structures, almost symmetric around the origin, are ohmic for V j j< 0:1 V and have a super-linear behavior (power law) for V j j< 0:1 V. The structure can be modeled as two diodes back to back connected so that the main current transport mechanisms are due to the reverse current of the diodes. To explain the measured C-V curves, the capacitance of the heterostructure is modeled as the series connection of the depletion capacitances of the two back to back connected SnO 2 :F/p-type a-Si:H and Mo/p-type a-Si:H junctions. We simulated the reverse I-V curves of the SnO 2 :F/p-type a-Si:H heterojunction at different temperatures by using the simulation software SCAPS 2.9.03. In the model the main transport mechanism is generation of holes enhanced by tunneling by acceptor-type interface defects with a trap energy of 0.4 eV above the valence bandedge of the p-type a-Si:H layer and with a density of 4.0 Â 10 13 cm À2. By using I-V simulations and the proposed C-V model the built-in potential (V bi ) of the SnO 2 :F/p-type a-Si:H (0.16 V) and p-type a-Si:H/Mo (0.14 V) heterojunctions are extracted and a band diagram of the characterized structure is proposed.

Role of electric field and electrode material on the improvement of the ageing effects in hydrogenated amorphous silicon solar cells

“…To test such concept we have performed reverse bias stress experiments in samples in which the TCO layer in contact with the p-type a-Si: H film has been replaced by a Mo film, in cells realized as described in the previous section. The use of Mo can give some advantage for the p-type a-Si:H/metal contact resistance and for the solar cell carrier lifetime (compared to FTO) [10,11], and it may be advantageous to fabricate a-Si:H solar cells on flexible substrates [12], and to realise plasmonic light trapping [21]. Fig.…”

“…In the case of the cells with Mo bottom contact the efficiencies were typically about 5% with open-circuit voltage of 0.85 V, short-circuit current densities of 12 mA/cm 2 and fill factor of 47%. The differences between these two types of cells are discussed in detail in references [10][11][12] and they are attributed to differences in substrate texture and photocarrier lifetime.…”

Transport mechanisms and effective Schottky barrier height of ZnO/a-Si:H and ZnO/μc-Si:H heterojunction solar cells

“…These values were found to better describe our experiments while keeping the best possible with common values shown in literature. [16][17][18][19][20][21][22][23][24][25][26][27] Models used for the simulations include Fermi-Dirac statistics and Shockley-Read-Hall recombination. Amorphous layers were represented by a continuous DOS in the bandgap composed of exponential functions for band tails into the bandgap.…”

Role of the Back Metal-Semiconductor Contact on the Performances of a-Si:H Solar Cells

“…Results are averages on 100 devices per type. To explain the experimental I-V characteristics a surface state density of 4.0×10 13 cm -2 , with a gaussian energy distribution peaked 0.4 eV above the valence band edge of the ptype a-Si:H layer has to be assumed [5].…”