All-inorganic double-metal perovskite materials have recently gained much attention due to their three dimensionality (3D) and non-toxic nature to replace lead-based perovskite materials. Among all those double perovskite materials, theoretical works have demonstrated that Cs AgBiBr shows high stability and possesses a suitable band gap for solar-cell applications. However, the film-forming ability of Cs AgBiBr is found to be the utmost challenge hindering its development in thin-film solar-cell devices. In this work, a high-quality Cs AgBiBr film with ultra-smooth morphology, micro-sized grains, and high crystallinity is realized via anti-solvent dropping technology and post-annealing at high temperature. After optimization, the first example of an inverted planar heterojunction solar-cell device based on Cs AgBiBr exhibits a power conversion efficiency of 2.23 % with V =1.01 V, J =3.19 mA/cm , and FF=69.2 %. Besides, the device shows no hysteresis and a high stability.

A conjugated large-volume cation is adopted as an additive to modify FASnI 3 film with much improved film quality. Lead-free PSC devices with PCE of 9.61% on 0.09 cm 2 and 7.08% on 1 cm 2 can be achieved. The PSC devices also show robust stability with self-healing ability. This work addresses the promise of Sn-based PSCs and takes a big step forward in the field of ecofriendly lead-free photovoltaic devices.

As a promising substitute for toxic lead-based perovskite, tin (Sn)based halide perovskite has drawn much attention for photovoltaic applications.However, unsatisfied open-circuit voltage (V OC ) and fill factor (FF) values of the available Sn-based perovskite solar cells (PSCs) remain a lingering cloud. In this work, we report a bilateral interfacial engineering strategy to fabricate 2D−3D bulk heterojunction Sn-based perovskite solar cells. Specifically, large cation PEAI and bifunctional LiF are evaporated at the bilateral interfaces of a FASnI 3 film. The presence of PEAI improves the V OC and FF of the PSCs via improved surface coverage and the formed 2D−3D bulk heterojunction structure, while the bifunctional LiF (i) lowers the work function of PEDOT:PSS and (ii) facilitates hole extraction at the ITO/PEDOT:PSS interface. This strategy enabled a power conversion efficiency (PCE) of 6.98% with a V OC of 0.47 V and FF of 0.74. Our findings will add critical building bricks toward efficient Snbased PSCs.