Theoretical optimization of defect density and band offsets for CsPbI2Br based perovskite solar cells

Abstract

The stability of Methyl-Ammonium (MA) and Formamidinium (FA) based perovskite solar cells (PSCs) has always been a matter of concern because of volatile nature of organic cations present in them. So, it becomes necessary to replace organic cations with inorganic non-volatile cations. Recently, lot of efforts have been put in to a new class of PSCs, CsPbX 3 (where, X= Br, I, Cl etc.) wherein organic cation is replaced by Caesium, to address the stability issue. Despite being more stable than their organic counterparts, the PCE of CsPbI 2 Br based PSCs is still low as compared to that offered by Methyl-Ammonium (MA) and Formamidinium (FA) based PSCs. In this paper, we have proposed a new CsPbI2Br based PSC structure having n-i-p architecture: FTO/Zn(O 0.3 , S 0.7 )/CsPbI 2 Br/HTL/Au. The proposed structure has been simulated using SCAPS software by employing new ETL Zn(O 0.3 , S 0.7 ) and various HTLs (spiro-OMeTAD, CuSCN, CuI and MoO 3 ). Initial simulations reveal that the proposed PSC achieves best PCE of 20.36%, when CuI is used as HTL. The impact of defect density ( N t ) in CsPbI 2 Br layer has been studied for various HTLs and optimum value of N t obtained as 1.0 × 10 11 cm -3 . Defect densities at ETL/CsPbI 2 Br and CsPbI 2 Br/HTL interfaces have also been optimised at values of 1.0 × 10 15 cm -3 and 1.0 × 10 15 cm -3 respectively. Finally, VBO and CBO at respective interfaces have also been optimized and the final proposed structure having Zn(O 0.3 , S 0.7 ) as ETL and CuI as HTL resulted in the PCE of 21.51% with V OC of 1.55 V, J SC of 15.21 mAcm -2 and FF of 90.77%, which are comparable to the Shockley-Queisser limit for CsPbI 2 Br perovskite solar cells, thereby, considerably enhancing the efficiency of inorganic perovskite solar cells. • CsPbI 2 Br based PSC with Zn(O 0.3 S 0.7 ) as an ETL is simulated. • HTLs including Spiro-oMeTAD, CuI, CuSCN and MoO 3 are implemented in simulated structure. • CuI found to be most efficient HTL among others. • Impact of defect density of absorber layer and with its interfaces is studied. • Band offsets optimization were done to maximise the performance of PSC. • Final parameters thus obtained are: V OC - 1.5579 V, J SC - 15.21 mAcm -2 , FF - 90.77% and PCE - 21.51%.