Constructing low-dimensional/three-dimensional (LD/3D) perovskite heterostructures through post-treatment of 3D perovskites is an effective strategy for passivating surface defects in perovskite solar cells. Organic ammonium halide salts are among the most widely used materials for converting the surface layer of 3D perovskite to LD perovskite via cation exchange. However, the formed LD perovskites typically adopt an in-plane orientation and exhibit high exciton binding energy, which can adversely impact interfacial charge transport and reduce the effectiveness of molecular defect passivation. Herein, we design and synthesize a non-halide ammonium salt of 1-naphthylmethylammonium tetrafluoroborate (NMABF₄) to inhibit the transformation reaction, enabling surface termination of perovskite films with functional molecules. The use of a relatively large cation enhances the barrier of cation exchange between ammonium salt and 3D perovskite. Moreover, the non-halide anion with a strong interaction with Pb²⁺ is introduced to prevent the formation of Pb-I octahedra, thereby preventing the formation of 2D perovskite. Therefore, NMABF₄ effectively terminates the perovskite surface. This approach not only simultaneously passivates defects with opposing charges on the perovskite surface but also prevents potential drawbacks associated with heterostructure-induced intercalation. As a result, a champion device efficiency of 25.38% can be achieved using NMABF₄-terminated perovskite, compared to 23.52% for the control device. Moreover, the unencapsulated device demonstrates excellent operational stability, retaining 80% of its initial efficiency after 2001 h of aging at the maximum power point under continuous one-sun illumination.

Charge transport materials constitute a relatively large portion of the cost in the production of perovskite solar cells (PSCs). Therefore, developing cheap and efficient charge transport materials is of great significance for the commercialization of PSCs. In this study, three low-cost hole transport materials (HTMs), specifically 4,4'-(3,3'-bis(4-methoxy-2,6-dimethylphenyl)-[2,2'-bithiophene]-5,5'-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (TP-H), 4,4'-(3,3'-bis(4-methoxy-2,6-dimethylphenyl)-[2,2'-bithiophene]-5,5'-diyl)bis(3-methoxy-N,N-bis(4-methoxyphenyl)aniline) (TP-OMe), and 4,4'-(3,3'-bis(4-methoxy-2,6-dimethylphenyl)-[2,2'-bithiophene]-5,5'-diyl)bis(3-fluoro-N,N-bis(4-methoxyphenyl)aniline) (TP-F), were designed and synthesized using a bulky group-substituted 2,2'-bithiophene core and methoxy- or F-functionalized triphenylamine derivatives. Compared to the HTMs without F atoms, TP-F using F substitution exhibited enhanced intermolecular packing, a lower highest occupied molecular orbital energy level, and increased hole mobility and conductivity. The PSC incorporating the doped TP-F as the hole transport layer achieved the highest power conversion efficiency (over 24%) among the three devices. The high performance of TP-F can be attributed to the passivation effect of S and F atoms on uncoordinated Pb²⁺ within the perovskite (PVSK) film, which significantly reduces the density of defect states and the incidence of trap-mediated recombination in PSCs. This study demonstrates the effectiveness of the 3,3'-bis(4-methoxy-2,6-dimethylphenyl)-2,2'-bithiophene building block for constructing cost-effective HTMs and highlights the impact of F substitution on enhancing the photovoltaic performance of PSCs.

Semi-transparent perovskite solar cells (ST-PSCs) have broad applications in building integrated photovoltaics. However, the stability of ST-PSCs needs to be improved, especially in n-i-p ST-PSCs since the doped 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9'-spirobifluorene (Spiro-OMeTAD) is unstable at elevated temperatures and high humidity. In this work, a π-conjugated polymer poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophene-2-yl)-benzo[1,2-b:4,5-b']dithiophene))-alt-(5,5-(1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl)benzo[1',2'-c:4',5'-c']dithiophene-4,8-dione)] (PBDB-T) is selected to form a polymer composite hole transport layer (HTL) with Spiro-OMeTAD. The sulfur atom of the thiophene unit and the carbonyl group of the polymer interact with the undercoordinated Pb²⁺ at the perovskite surface, which stabilizes the perovskite/HTL interface and passivates the interfacial defects. The incorporation of the polymer also increases the glass transition temperature and the moisture resistance of Spiro-OMeTAD. As a result, we obtain ST-PSCs with a champion efficiency of 13.71% and an average visible light transmittance of 36.04%. Therefore, a high light utilization efficiency of 4.94% can be obtained. Moreover, the encapsulated device can maintain 84% of the initial efficiency after 751 h under continuous one-sun illumination (at 30% relative humidity) at the open circuit and the unencapsulated device can maintain 80% of the initial efficiency after maximum power tracking for more than 1250 h under continuous one-sun illumination.