Perovskite solar cells

A solar cell comprising, from bottom to top, a support layer;

• an electron transporting layer;
• a 3D perovskite layer;
• a multifunctional 2D perovskite capping layer;
• a hole transporting layer;
• and a counter electrode layer, wherein the 2D perovskite capping layer comprises an organic-inorganic hybrid perovskite of Formula I:
• (R1NH3+)2(A+)n−1(M2+)n(X−)3n+1 I
• wherein:
• (R1NH3+) represents an asymmetric mono-ammonium cationic moiety:
• A+ represents a cation Cs+, Rb+, CH3NH3+, CH3CH2NH3+, or
• R2 is —H, —F, —Cl, —Br, —I, —Me, —Et, —OMe, —OEt, —SMe, —SEt, —CN, —NO2, —COMe, —CHO, —COOMe, or —NH—COMe;
• (Ar)m represents a conjugated and optionally substituted aryl or hetero aryl system, or a combination thereof, wherein each aryl or hetero aryl ring in the conjugated and optionally substituted aryl or hetero aryl system may be same or different;
• M2+ represents a divalent metal cation Pb2+, Sn2+, Ge2+, Cu2+, Zn2+, Cd2+, Hg2+, Ni2+, Co2+, Fe2+, Mn2+, Cr2+, V2+, Pd2+, Pt2+, or a combination thereof;
• or a combination of one monovalent metal cation selected from the group consisting of Ag+, Cu+, Tl+, Au+, and one trivalent metal cation selected from the group consisting of Bi3+, Sb3+, In3+, As3+, Au3+, Y3+, to make the average valence of the metal cation to be 2+;
• X is F, Cl, Br or I;
• l is 1-4;
• m is 0-5;
• and
• n is 1-6;
• wherein the positions of R2 and (Ar)m on the thiophenyl ring can be exchanged;
• where the 2D perovskite capping layer is the interfacial layer which supports interface charge transfer;
• where the 3D perovskite layer is light absorbing material and the major light absorbing layer;
• and
• where the 3D perovskite layer and multifunctional 2D perovskite capping layer form a 2D/3D perovskite heterostructure which supports interface charge transfer.