Structural Design And Carrier Dynamics Of Perovskite Solar Cell Materials

The discovery and application of solar cell materials has been a subject of continuous concern for more than half a century,reflecting the tireless pursuit of renewable and clean energy sources by human society.Tetrahedral coordination structures,e.g.crystalline Si,GaAs,CdTe,CuInSe2,Cu2ZnSnSe4,and octahedral coordination structures,e.g.perovskites,have represented two classes of successful crystal structures hitherto for solar cell absorbers Via the first-principles calculations and crysta symmetry analysis,the two classes of semiconductors are shown exhibiting complementary properties in terms of bond covalency/iconicity,optical property,defect tolerance,and stability,which are correlated with their respective coordination number.Therefore,a spinel structure is proposed,which combines tetrahedral and octahedral coordination into a single crystal structure,as an alternative to perovskite and conventional semiconductors for potential photovoltaic application.The case studies of a class of 105 spinel AB2X4 systems(A=Mg2+,Ca2+,Sr2+,Ba2+,Zn2+,Cd2+,Hg2+;B=Sc3+,Y3+,Al3+,Ga3+,In3+;X=O2-,S2-,Se2-)identify five spinel compounds HgAl2Se4,HgIn2S4,CdIn2Se4,HgSc2S4,and HgY2S4 as promising solar cell absorbers.In particular,HgAl2Se4 has suitable bandgap(1.36 eV),small direct-indirect bandgap difference(24 meV),appropriate carrier effective mass(me*?0.08 m0,and mh*=0.69 m0),strong optical absorption,and high dynamic stability.This study suggests that crystal systems with mixed tetrahedral and octahedral coordination may open a viable route for emerging solar cell absorbers.In the basic research of perovskite solar cell materials,we find that alloying plays a certain role in inhibiting the carrier recombination of perovskites,which effectively improves the conversion efficiency of solar cells.Using time domain density functional theory(TD-DFT)combined with non-adiabatic molecular dynamics(NAMD),correlation on recombination lifetime of the charge carrier in three organic-inorganic hybrid perovskites,HC(NH2)2PbI3(FAPbI3),Cs0.25FA0.75PbI3 and Cs0.25FA0.75PbI2.76Br0.24,was studies.The results show that the recombination lifetime for the mixed perovskite systems slower than that of the pristine FAPbI3,this is because mixed systems are beneficial to reduce the overlap between electron and hole wave functions.Besides,due to the small sub-1 meV non-adiabatic coupling(NAC)and short sub-11 fs coherence times,the non-radiative electron-hole recombination proceeds slowly,which consistent with the trend observed in the experiment.The time-domain atomistic simulations advance our understanding for mixed perovskites on the excited-state lifetimes.