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This research work contributes to the numerical simulation of Pb-free double perovskite NaZn 0 · 7 Ag 0.3 Br 3 -based perovskite solar cells via SCAPS 1D. For the initial simulation, TiO 2 and PEDOT:PSS is considered as an initial charge transport layer with the device efficiency reaching up to 13.44 %. Further, the impact of different ETL and HTL is studied and optimized. The optimization is performed by correlating the V bi with the V OC. There is a strong relationship is obtained between the V bi with the V OC. It is thus revealed from the simulation that to conveniently transport electrons the E CB_ETL should lie below E CB_PVK. However, for convenient transport of holes, the E VB_HTL should lie above E VB_PVK. Using this concept, the optimized ETL and HTL obtained are ZnSe and ZnTe. Moreover, the influence of the thickness of the Pb-free double perovskite is also realized with the optimized thickness obtained as 700 nm which improves device efficiency to 27.59 % and other photovoltaic parameters as V OC = 1.59 V, J SC = 21.90 mA/cm2, FF = 78.92 % with the optimized structure as (FTO/ZnSe/NaZn 0.7 Ag 0 · 3 Br 3 /ZnTe/Au). Thus, the proposed results reveal that the Pb-free double perovskite NaZnBr 3 (NaZn 0 · 7 Ag 0.3 Br 3) based perovskite solar cell is considered one of the most intriguing candidates for future perovskite solar cell applications. • The simulation of the Pb-Free NaZnBr 3 (NaZn 0.7 Ag 0.3 Br 3) based perovskite solar cell is performed. • The charge transport layers are optimized based on their relation between the built-in potential and the V OC. • The VB and CB position of the ETL and HTL corresponds to the perovskite absorber layer shows a significant impact on the device performance. • The ZnTe and ZnSe as a hole and electron transport layer elevates device efficiency up to 27.02 %. • After optimization, the device efficiency improves up to 27.59 % of Pb-Free NaZnBr 3 (NaZn 0.7 Ag 0.3 Br 3) perovskite solar cell. [ABSTRACT FROM AUTHOR]

• All- perovskite lead –free tandem solar cell is simulated with efficiency 26.73%. • CH 3 NH 3 GeI 3 & FAMASnGeI 3 perovskite layers have been used. • Different elctron transport layers have been studied. • The impact of defect density and front electrode work function is also studied. The numerical simulation of lead-free all-perovskite tandem solar cell using solar capacitance one dimensional tool (SCAPS 1D) has been performed. The combination of methyl ammonium germanium halide (CH 3 NH 3 GeI 3) as wide band-gap (1.9 eV) perovskite layer and FA 0.75 MA 0.25 Sn 0.25 Ge 0.5 I 3 (FAMASnGeI 3) as a low band-gap (1.4 eV) perovskite layer is considered for the first time which shows the optimal device efficiency of 26.72%. The present work studies the effect of the different electron transport layer, perovskite absorber thickness and its defect density on photovoltaic performance. Further, the effect of front electrode work function on the device photovoltaic performance is also studied. It has been observed that the device open circuit voltage (Vo C) is significantly affected by the built-in voltage (V bi) across the perovskite layer. In addition, the effect of thickness of the perovskite absorber layers is also investigated. Moreover, the effect of defect density of the absorber layer is also explored, and it has been found that for better device performance the defect density needs to be as low as possible. Furthermore, it has been observed that the work function of the front contact plays a significant role and for the proposed device its value should not be more than 4.4 eV. The proposed all–perovskite tandem solar cell shows the remarkable photovoltaic parameters i.e., open circuit voltage (V OC) = 1.07 Volts, short circuit current density (J SC) = 28.36 mA/cm2, fill factor (FF) = 84.39% and efficiency (η) = 26.72%. [ABSTRACT FROM AUTHOR]

The present study investigates the effect of band offsets engineering for lead–free (Pb-free) all-inorganic double-perovskite solar cell (DPSC) using the solar cell capacitance simulator one dimensional (SCAPS 1D). The initial simulation study is carried out by using Cs 2 AgBi 0.75 Sb 0.25 Br 6 based double-perovskite layer along with 2,2′,7,7′-tetrakis[N,N-di4-methoxyphenylamino]-9,9′-spirobifluorene (SpiroOMeTAD) as a hole transport layer (HTL) and zinc oxide (ZnO) as an electron transport layer (ETL) which shows the device efficiency of 11.35%. Further, the impact of the conduction band offset (CBO) and valence band offset (VBO) is studied to improve the device performance. The proposed study suggests that extremely negative and positive CBO resulted in limited PV performance. This is mainly due to the reason that in extremely negative CBO limits the V bi and thus V OC. However, the extreme positive CBO leads to the formation of a barrier spike which restricts the device performance. Similarly, the positive VBO leads to band misalignment which further deteriorates the device performance. Hence, it has been revealed from the numerical simulation, that the optimum conduction band offset (CBO) is found to be −0.1 eV to +0.1 eV and the optimum valence band offset (VBO) is found to be −0.1 eV–0.00 eV with respect to the double-perovskite absorber layer. It has been found that with the introduction of copper (I) thiocyanate (CuSCN) as a hole transport layer (HTL) and zinc oxysulfide (ZnOS) as an ETL the overall power conversion efficiency (PCE) improves up to 18.26% which is an outstanding improvement in the lead-free double–perovskite solar cell. In addition, the effect of the thickness of the perovskite layer is also studied in which the optimized double-perovskite layer thickness obtained is 400 nm. Thus, the proposed simulation study provides significant insight for the researchers that will help to find out the suitable ETL and HTL for Pb-free DPSC. • Band offset engineering is analyzed to improve the performance of double–perovskite solar cells. • The range of optimum CBO and VBO is obtained is −0.1eV–0.1eV and −0.1 eV–0.00 eV respectively. • The effect of thickness of the Pb-free double-perovskite layer on the photovoltaic performance is also investigated. • The final device efficiency of double–perovskite solar cell reaches up to 18.26%. [ABSTRACT FROM AUTHOR]

This article presents the numerical simulation of lead–free (Pb-free) double–perovskite (Cs 2 AgBi 0.75 Sb 0.25 Br 6 , i.e., mixed antimony bismuth halide double-perovskite) solar cell (DPSC) using solar cell capacitance one dimensional simulator (SCAPS-1D). In this contribution, the hole transport layers (HTLs) and electron transport layers (ETLs) are optimized. The optimization is performed by correlating the open circuit voltage (V OC) with the built-in potential (V bi). It is disclosed from the simulation results, that higher V bi resulted higher V OC. Furthermore, it is also found that, for the proper selection of HTL, the E V_HTL (Valence band maximum of HTL) and φ BC (Work function of back contact) should not be much deeper than the E V_PVK (Valence band maximum of double–perovskite layer) to avoid V bi loss. Correspondingly, for proper selection of ETL, E C_ETL (Conduction band minimum of electron transport layer) and Φ FC (Work function of front contact), should not be much higher than E C_PVK to prevent V bi loss. The optimized HTL and ETL are found to be Cu 2 O (copper(I) oxide) and ZnOS (Zinc oxysulfide) respectively. Moreover, the device photovoltaic performance is further improved by optimizing the double-perovskite layer thickness which is found to be 400 nm. Under optimized condition, the device photovoltaic power conversion efficiency (η) improves to 18.18%. The optimized device photovoltaic performance are found to be, open –circuit voltage (Voc) = 1.39 V, short-circuit current density (J SC) = 16.04 mA/cm2, and fill factor (FF) = 78.34% which indicates that double–perovskite absorber layer (Cs 2 AgBi 0.75 Sb 0.25 Br 6) is a suitable candidate for the development of highly efficient Pb-free DPSC. • The numerical simulation of lead-free double–perovskite is performed with-optimized device efficiency of 18.18%. • The electron transport layer and hole transport layer is optimized by co-orelating V OC with V bi. • The simulation study reveals that V OC is strongly dependent on V bi of lead-free double –perovskite absorber layer. • The optimized ETL and HTL found to be ZnOS and Cu 2 O respectively. [ABSTRACT FROM AUTHOR]

The numerical simulation of lead-free perovskite cesium tin germanium halide (CsSnGeI 3) and methyl ammonium germanium halide (CH 3 NH 3 GeI 3) solar cells have been performed. It has been elucidated from the numerical simulation that as compare to the CH 3 NH 3 GeI 3 based structure, CsSnGeI 3 based structure depicts better photovoltaic performance under constant illumination condition. To enhance the device photovoltaic performance, the effects of different hole transport layer (HTL), defect density of the absorber layer, metal work function and the effect of temperature has been studied. In the present investigation, the effect of hole transport layers are analyzed by correlating the built-in voltage (V bi) with the open circuit voltage (V OC). It has been obtained from the simulation results, that V bi has a significant impact on V OC as the higher V bi corresponds to the highest V OC. Moreover, the effect of defect density and metal work function is also studied. It is obtained from the simulation results, that the optimum defect density is found to be 1 × 1014 cm−3 and metal work function should be greater than or equal to 5 eV for both lead-free CH 3 NH 3 GeI 3 and CsSnGeI 3 based perovskite layer. Furthermore, to suggest possible lead-free alternatives for all-perovskite two-terminal multi-junction solar cell, an attempt is made to match the current of bottom perovskite layer i.e., CsSnGeI 3 based perovskite layer to the top perovskite layer i.e., CH 3 NH 3 GeI 3 based perovskite layer. To attain the current matching for bottom perovskite layer (CsSnGeI 3 based perovskite layer) to top perovskite layer (CH 3 NH 3 GeI 3 based perovskite layer), the bottom perovskite sub cell is fed with the filtered spectrum which is obtained by transmission from top electrode. After, the realization of current matching the short circuit current density of CsSnGeI 3 based perovskite layer drops from 25.75 mA/cm2 to 15.32 mA/cm2 which is similar to CH 3 NH 3 GeI 3 based perovskite absorber layer. In addition, it has been obtained from literature, that both the perovskite layers can be fabricated using solution–processing low-temperature technology. Hence, the numerical study suggests the possible alternatives for wide and narrow bandgap perovskite layers for the application to obtain highly efficient lead-free all-perovskite multi-junction solar cells. • The numerical simulation of lead-free wide and narrow bandgap CH 3 NH 3 GeI 3 and CsSnGeI 3 perovskite layers is performed. • The effect of different hole transport layers is realized by correlating V bi with the V OC. • Cu 2 O as an HTL shows highest V bi and hence shows better photovoltaic performance. • The study of defect density, metal work function and temperature are explored for lead-free perovskite layers. • The lead-free perovskite layers proves to be the promising candidate for all-perovskite multi-junction solar cell. [ABSTRACT FROM AUTHOR]