Influence of the transparent conductive oxide layer deposition step on electrical properties of silicon heterojunction solar cells

Abstract

International audienceThis work deals with the understanding of the transport behavior of different deposited Indium Tin Oxide (ITO) layers on the emitter of n-type heterojunction solar cells. A complete study based on effective lifetime measurements has been carried out on samples with different ITO thicknesses to evaluate the passivation quality before and after ITO deposition, showing that increasing the ITO thickness degrades the passivation properties only at low injection level. Further characterizations coupled with numerical simulations demonstrate that such a behavior is due to recombination at the ITO/(p) a-Si:H interface induced by the ITO layer

Transparent Electrodes in Silicon Heterojunction Solar Cells: Influence on Contact Passivation

“…Earlier, it was already established that deposition of TCOs on ip stacks (i.e., hole collectors) can result in additional Δn dependences of the wafer surface passivation [27]- [30], leading to a reduction in τ eff values at low Δn values (Δn < 10 15 cm −3 ). This was reported for a variety of TCOs, including aluminum doped zinc oxide (ZnO:Al) [27], [29], [30] and ITO films [28], [29]. Numerical simulations suggested that the τ eff variation at low Δn is caused by the presumed existence of an ultrathin highly defective (recombination-active) layer in-between the a-Si:H(p) layer and ITO [28].…”

“…This was reported for a variety of TCOs, including aluminum doped zinc oxide (ZnO:Al) [27], [29], [30] and ITO films [28], [29]. Numerical simulations suggested that the τ eff variation at low Δn is caused by the presumed existence of an ultrathin highly defective (recombination-active) layer in-between the a-Si:H(p) layer and ITO [28]. However, although some TCO deposition methods can cause damage to underlying films [31], the described τ eff variations were also observed using ultrasoft deposition techniques such as atomic layer deposition [29], [30], and vanished after TCO removal via chemical etching [27], [30].…”

Impact of sputter-induced ion bombardment at the heterointerfaces of a-Si:H/c-Si solar cells with double-layered In2O3:Sn structures

“…The reason for the P bottom rf -independent trend of V oc is likely to be as follows: the degraded electrical properties of a-Si:H=c-Si heterostructures can be improved drastically by thermal annealing as reported previously. [18][19][20][21] In our case, the defects (recombination centers) are also generated by the sputter-induced ion bombardment; however, most of them are sufficiently eliminated after the annealing. As a result, V oc seems to be not significantly affected by the sputtering damage.…”

“…18) So far, it has been reported that the carrier lifetime of a-Si:H=c-Si heterostructures is significantly shortened by the sputtering deposition of TCO layers. [18][19][20][21] Nevertheless, there have been only a few studies that demonstrated the direct observation of the impact of sputter-induced ion bombardment on the photovoltaic characteristics. 18) This is much more likely attributed to the difficulty in separating the two simultaneous effects on the photovoltaic characteristics; one is the sputter-induced ion bombardment of the underlying a-Si:H layer and the other is the change in the electrical properties of the deposited ITO layer.…”

Impact of organic overlayers on a-Si:H/c-Si surface potential

“…The latter is manifested by a reduced c-Si surface potential (and thus field effect), resulting in a reduced effective minoritycarrier lifetime (s eff ) at low-to-moderate Dn values and hence potentially lower fill factors (FF). 7,11,12,[18][19][20][21][22] This issue may be circumvented by employing an additional buffer layer that features higher WF values, compared to the p-type a-Si:H hole collectors. In this context, hole-collecting organic semiconductors (OSCs) are promising candidates to be applied at the hole collecting side in order to improve the band alignment at the wafer interface.…”