Dopant-free polymeric hole-transporting materials for perovskite solar cell

1. A hybrid organic-inorganic perovskite photovoltaic device comprising a first electrode, a second electrode, a light-absorbing layer between the first and second electrodes that comprises a perovskite compound, and a hole-transporting material in contact with the perovskite compound, wherein the hole-transporting material comprises a copolymer comprising a benzo[1,2-d;4,5-d′]bistriazole-containing repeating unit and a benzo[1,2-b:4,5-b′]dithiophene-containing repeating unit.

2. The device of claim 1 , wherein the copolymer comprises a repeating unit represented by formula (I):

wherein:

R 1 , at each occurrence, independently is a solubilizing group;

R 2 , at each occurrence, independently is selected from the group consisting of H, F, Cl, CN, and a C 1-40 alkyl or haloalkyl group;

R 3 and R 4 , at each occurrence, independently are selected from the group consisting of H, F, Cl, and -L-(Ar) m -L′-R 5 , wherein L and L′, independently are selected from the group consisting of —O—, —S—, —Se—, —C(O)—, —OC(O)—, —C(O)O—, a divalent C 1-40 alkyl or haloalkyl group, and a covalent bond; R 5 is a solubilizing group; Ar, at each occurrence, independently is a C 6-14 aryl group or a 5-14 membered heteroaryl group, each of which optionally is substituted with 1-4 -L′-R 5 groups; and m is 0, 1, 2, 3 or 4; and

q and q′ independently are 0, 1, 2, 3 or 4.

3. The device of claim 2 , wherein each of the solubilizing group independently is selected from the group consisting of a C 3-40 alkyl group, a C 3-40 alkenyl group, and a C 3-40 haloalkyl group.

4. The device of claim 2 , wherein the copolymer comprises a repeating unit represented by formula (II):

wherein each R 1 is a C 3-40 alkyl group.

5. The device of claim 4 , wherein each R 3 is an —O—C 3-40 alkyl group.

6. The device of claim 4 , wherein each R 3 is a C 3-40 alkyl group.

7. The device of claim 4 , wherein each R 3 is —(Ar)-L′-R 5 , wherein Ar is a thienyl or phenyl group, L′ is O or a covalent bond; and R 5 is a C 3-40 alkyl group.

8. The device of claim 7 , wherein each R 3 is a -phenyl-O—C 3-40 alkyl group.

9. The device of claim 7 , wherein each R 3 is a -thienyl-C 3-40 alkyl group.

10. The device of claim 1 , wherein the hole-transporting material is free of any dopants.

11. The device of claim 1 , wherein the hole-transporting material is free of a dopant selected from the group consisting of 4-tert-butylpyridine (TBP), bis(trifluoromethane)sulfonimide lithium salt (Li-TFSI), and tris(2-(1H-pyrazol-1-yl)4-tert-butylpyridine)cobalt(III) tris(bis(trifluoromethylsulfonyl)imide) (FK209).

12. The device of claim 1 , wherein the perovskite compound has the formula ABX 3 , wherein A is CH 3 NH 3 + or HN═CHNH 3 + , B is Sn 2 + or Pb 2 + , and each X independently is selected from I − , Br − , and Cl − .

13. The device of claim 12 , wherein the perovskite compound is CH 3 NH 3 PbI 3 or CH 3 NH 3 PbI 3-x Cl x , where x is 1 or 2.

14. The device of claim 1 having a planar structure, wherein the light-absorbing layer is a thin film comprising the perovskite compound.

15. The device of claim 14 further comprising a blocking layer between one of the first and second electrodes and the light-absorbing layer.

16. The device of claim 15 , wherein the blocking layer comprises TiO 2 or ZnO.

17. The device of claim 14 comprising a transparent conducting oxide as the first electrode, wherein the transparent conducting oxide is fluorine-doped tin oxide (FTO).

18. The device of claim 14 comprising a metal as the second electrode, wherein the metal is Au or Ag.