Liftoff process for exfoliation of thin film photovoltaic devices and back contact formation
A method for forming a back contact on an absorber layer in a photovoltaic device includes forming a two dimensional material on a first substrate. An absorber layer including Cu—Zn—Sn—S(Se) (CZTSSe) is grown over the first substrate on the two dimensional material. A buffer layer is grown on the absorber layer on a side opposite the two dimensional material. The absorber layer is exfoliated from the two dimensional material to remove the first substrate from a backside of the absorber layer opposite the buffer layer. A back contact is deposited on the absorber layer.
1. A method for forming a back contact on an absorber layer in a photovoltaic device, comprising:
forming a two dimensional material on a first substrate;
growing an absorber layer including Cu—Zn—Sn—S(Se) (CZTSSe) over the first substrate on the two dimensional material;
growing a buffer layer on the absorber layer on a side opposite the two dimensional material;
exfoliating the absorber layer from the two dimensional material to remove the first substrate from a backside of the absorber layer opposite the buffer layer; and
depositing a back contact on the absorber layer.
2. The method as recited in claim 1 , wherein the first substrate includes a metal coated glass.
3. The method as recited in claim 1 , wherein the two dimensional material includes one or more monolayers of graphene.
4. The method as recited in claim 1 , further comprising adhering the back contact to a flexible substrate to form a flexible photovoltaic device.
5. The method as recited in claim 1 , wherein exfoliating the absorber layer includes mechanically splitting the absorber layer from the two dimensional material.
6. The method as recited in claim 1 , wherein exfoliating the absorber layer includes thermally splitting the absorber layer from the two dimensional material.
7. The method as recited in claim 1 , further comprising forming a transparent conductor over the buffer layer.
8. The method as recited in claim 7 , further comprising forming metal structures on the transparent conductor.
9. A method for forming a flexible photovoltaic device, comprising:
forming graphene on a metal coated glass substrate;
growing an absorber layer including Cu—Zn—Sn—S(Se) (CZTSSe) over the first substrate on the graphene;
growing a buffer layer on the absorber layer on a side opposite the graphene;
forming a transparent conductor over the buffer layer;
exfoliating the absorber layer from the graphene to remove the metal coated glass substrate from a backside of the absorber layer opposite the buffer layer;
cleaning the backside of the absorber layer;
depositing a back contact on the absorber layer; and
adhering the back contact to a flexible substrate to form a flexible photovoltaic device.
10. The method as recited in claim 9 , wherein the graphene includes one or more monolayers.
11. The method as recited in claim 9 , wherein exfoliating the absorber layer includes mechanically splitting the absorber layer from the graphene.
12. The method as recited in claim 9 , wherein exfoliating the absorber layer includes thermally splitting the absorber layer from the graphene.
13. The method as recited in claim 9 , further comprising forming metal structures on the transparent conductor.
14. The method as recited in claim 9 , further comprising forming an antireflection coating on the transparent conductor.