On the CdS/CuInSe2 conduction band discontinuity

Abstract

Recent calculations of the electron affinity difference between CdS and CuInSe2 indicate that the conduction band (CB) minimum of CuInSe2 is below the CB minimum of CdS. As a consequence, a spike occurs in the CB at the CdS/CuInSe2 interface. Such a spike is commonly considered as in conflict with good photovoltaic performance of heterojunction solar cells. It is outlined here that the simple assumption of thermionic emission across the junction can explain an unimpeded electron transport in the case of an n+p structure (n-type window, p-type absorber), even when a spike in the CB occurs.

Enhancing the efficiency of SnS solar cells via band-offset engineering with a zinc oxysulfide buffer layer

“…20 According to device simulations, a large negative CBO gives rise to an increase in the interface recombination, while a large positive CBO greater than +0.5 eV creates a barrier in the conduction band that impedes the collection of photo-generated electron. 21,22 Thus, a small positive CBO is desirable to reduce interface recombination without any loss in photo-current collection. 21,22 One of the approaches to adjust the CBO is to vary the constituent elements in the semiconductor-alloy buffer layer.…”

“…21,22 Thus, a small positive CBO is desirable to reduce interface recombination without any loss in photo-current collection. 21,22 One of the approaches to adjust the CBO is to vary the constituent elements in the semiconductor-alloy buffer layer. For example, (Zn,Cd)S, 23 (Zn,Mg)O, 24 (Zn,Sn)O x , 25 and Zn(O,S) 26 were used in an attempt to replace CdS in CIGS solar cells.…”

Determination of band offsets at the Al:ZnO/Cu2SnS3 interface using X-ray photoelectron spectroscopy

“…A spike is usually considered ideal for a solar cell device since it prevents recombination of charge carriers at the interface. 19,20 In this case the conduction band minimum of AZO is above that of CTS leading to an increase in the interface bandgap, thus leading to a reduction in the interface recombination. Due to the reduction in interface recombination, the open circuit voltage V oc would increase.…”

Towards high performance Cd-free CZTSe solar cells with a ZnS(O,OH) buffer layer: the influence of thiourea concentration on chemical bath deposition

“…Furthermore, this small spike has no negative influence on electron transport as theoretical calculation shows assuming thermionic emission across the junction. [3][4][5] In contrast, a too high spike in the conduction band will act as barrier for electrons, and therefore drastically reduce short circuit current (J sc ). The absence of a spike,…”