2D/3D Heterostructure for Semitransparent Perovskite Solar Cells with Engineered Bandgap Enables Efficiencies Exceeding 25% in Four‐Terminal Tandems with Silicon and CIGS

Abstract

Wide-bandgap perovskite solar cells (PSCs) with optimal bandgap (E g ) and high power conversion efficiency (PCE) are key to high-performance perovskite-based tandem photovoltaics. A 2D/3D perovskite heterostructure passivation is employed for double-cation wide-bandgap PSCs with engineered bandgap (1.65 eV ≤ E g ≤ 1.85 eV), which results in improved stabilized PCEs and a strong enhancement in open-circuit voltages of around 45 mV compared to reference devices for all investigated bandgaps. Making use of this strategy, semitransparent PSCs with engineered bandgap are developed, which show stabilized PCEs of up to 25.7% and 25.0% in fourterminal perovskite/c-Si and perovskite/CIGS tandem solar cells, respectively. Moreover, comparable tandem PCEs are observed for a broad range of perovskite bandgaps. For the first time, the robustness of the four-terminal tandem configuration with respect to variations in the perovskite bandgap for two state-of-the-art bottom solar cells is experimentally validated.

Triple-cation low-bandgap perovskite thin-films for high-efficiency four-terminal all-perovskite tandem solar cells

“…The semitransparent PSC composed of a 2D/3D perovskite heterostructure has a regular conguration of glass/ITO/SnO 2 nanoparticles (np-SnO 2 )/Cs 0.17 FA 0.83 Pb(I 0.76 Br 0.24 ) 3 /2,2 0 ,7,7 0 -tetrakis [N,N-di(4-methoxyphenyl)amino]-9,9 0 -spirobiuorene (spiro-MeOTAD)/molybdenum oxide (MoO x )/ITO/magnesium uoride (MgF 2 ). 8 MoO x (10 nm) is to protect the spiro-MeOTAD layer against ion bombardment during the subsequent ITO sputtering process. 74,75 In addition, an MgF 2 thin-lm (165 nm) on the sputtered ITO acts as an anti-reection to increase the optical transmittance.…”

“…4 and 5) and 1.5-2.3 eV (ref. [6][7][8] by tuning the Sn : Pb and I : Br ratio, respectively. Therefore, this class of materials is suited for both WBG top and LBG bottom solar cells in an all-perovskite tandem solar cell (all-PTSC) conguration.…”

Choose Your Own Adventure: Fabrication of Monolithic All‐Perovskite Tandem Photovoltaics

“…[ 97,98 ] Currently, the highest PCE for a wide‐ E g (≥1.7 eV) perovskite solar cell is 19.8% for a 1.72 eV butylammonium bromide (BABr) treated FA 0.83 Cs 0.17 Pb(I 0.6 Br 0.4 ) 3 [ 99 ] and there are 8 other reported compositions with >18% PCE. [ 51,100–106 ] We note that this record wide‐ E g perovskite has not yet been incorporated into an all‐perovskite monolithic tandem but has been used in a 4T perovskite‐Si and CIGS tandem. [ 104 ] For perovskites with an E g ≥1.75 eV, the PCEs remain relatively high, with 4 reports of devices ≥17% PCE, [ 30,107–109 ] but for the widest gaps, E g of ≥1.8 eV the highest PCE is 16.3%.…”

“…[ 51,100–106 ] We note that this record wide‐ E g perovskite has not yet been incorporated into an all‐perovskite monolithic tandem but has been used in a 4T perovskite‐Si and CIGS tandem. [ 104 ] For perovskites with an E g ≥1.75 eV, the PCEs remain relatively high, with 4 reports of devices ≥17% PCE, [ 30,107–109 ] but for the widest gaps, E g of ≥1.8 eV the highest PCE is 16.3%. [ 50 ] Note that a 1.7 eV solar cell can theoretically still reach 28.6% and an 1.8 eV solar cell could reach 26.8%, thus this fast drop off in PCE with an increase in E g over 1.75 eV is not due simply to charge thermalization constraints.…”

“…[ 113 ] Only two wide‐ E g perovskite solar cells have reached a % V OC‐SQ of ≥90%: CsPbI 3 quantum dots (QDs) have reached a V OC of 1.28 V and the BABr treated FA 0.83 Cs 0.17 Pb(I 0.6 Br 0.4 ) 3 reached a V OC of 1.31 V. [ 99,114 ] A total of 13 other perovskites with an E g ≥1.7 eV have reached a % V OC‐SQ of ≥85% [ 51,100,101,103–108,115,116 ] and 5 solar cells with an E g of ≥ 1.8 eV have % V OC ‐ SQ of >80%. [ 50,103,104,117 ] Additionally, nearly all of these reports use some sort of additive or surface treatment including BABr, [ 99,104 ] KI, [ 109 ] Pb(SCN) 2 , [ 103,105,107 ] dimethylammonium (DMA), [ 51 ] choline iodide, [ 102 ] benzylamine, [ 101 ] guanidinium bromide (GuaBr), [ 105 ] formamide, [ 108 ] or an alkylammonium halide [ 115 ] suggesting that surface passivation is key to both a high V OC and a high efficiency. While great strides in improving the V OC have been made within the last year, these % V OC‐SQ values are still relatively low compared to the mid‐ E g (≈1.5–1.6 eV) perovskites, many of which have reached a % V OC‐SQ >90%, [ 34,74,109,118–122 ] even up to 95%.…”