The accelerated research on perovskite solar cells (PSCs) can strongly promote the transition from fossil to alternative renewable energy sources. [1][2][3][4] The remarkable optoelectronic properties including high absorption coefficient, large diffusion lengths, and high carrier mobility render perovskite Today's perovskite solar cells (PSCs) mostly use components, such as organic hole conductors or noble metal back contacts, that are very expensive or cause degradation of their photovoltaic performance. For future large-scale deployment of PSCs, these components need to be replaced with costeffective and robust ones that maintain high efficiency while ascertaining long-term operational stability. Here, a simple and low-cost PSC architecture employing dopant-free TiO 2 and CuSCN as the electron and hole conductor, respectively, is introduced while a graphitic carbon layer deposited at room temperature serves as the back electrical contact. The resulting PSCs show efficiencies exceeding 18% under standard AM 1.5 solar illumination and retain ≈95% of their initial efficiencies for >2000 h at the maximum power point under full-sun illumination at 60 °C. In addition, the CuSCN/carbon-based PSCs exhibit remarkable stability under ultraviolet irradiance for >1000 h while under similar conditions, the standard spiro-MeOTAD/Au based devices degrade severely.

The performance of perovskite solar cells is highly dependent on the fabrication method; thus, controlling the growth mechanism of perovskite crystals is a promising way towards increasing their efficiency and stability. Herein, a multi‐cation halide composition of perovskite solar cells is engineered via the two‐step sequential deposition method. Strikingly, it is found that adding mixtures of 1D polymorphs of orthorhombic δ‐RbPbI3 and δ‐CsPbI3 to the PbI2 precursor solution induces the formation of porous mesostructured hexagonal films. This porosity greatly facilitates the heterogeneous nucleation and the penetration of FA (formamidinium)/MA (methylammonium) cations within the PbI2 film. Thus, the subsequent conversion of PbI2 into the desired multication cubic α‐structure by exposing it to a solution of formamidinium methylammonium halides is greatly enhanced. During the conversion step, the δ‐CsPbI3 also is fully integrated into the 3D mixed cation perovskite lattice, which exhibits high crystallinity and superior optoelectronic properties. The champion device shows a power conversion efficiency (PCE) over 22%. Furthermore, these devices exhibit enhanced operational stability, with the best device retaining more than 90% of its initial value of PCE under 1 Sun illumination with maximum power point tracking for 400 h.

Hole transport materials (HTM) are an important component in perovskite solar cells (PSC). Despite a multitude of HTMs developed in recent years, only few of them lead to solar cells with efficiencies over 20%. Therefore, it is still a challenge to develop high‐performing HTMs, which have ideal energy levels of the frontier orbitals, are highly efficient in transporting charges, and stabilize the solar cell at the same time. In this work, the development of a structurally novel molecular HTM, CPDA 1, is described which is based on a common cyclopentadiene core and can be efficiently and inexpensively synthesized from readily available starting materials, which is important for future realization of low‐cost photovoltaics on larger scale. Due to excellent optoelectronic, thermal, and transport properties, CPDA 1 not only meets the envisioned properties by reaching high efficiencies of 23.1%, which is among the highest reported to date, but also contributes to a respectable long‐term stability of the PSCs.

The defects present in metal halide perovskite are deleterious to both the performance and stability of photovoltaic devices. Consequently, there is an intense focus on developing defect mitigation strategies. Herein we report a facile strategy that employs methylammonium triiodide (MAI3) as an additive to the perovskite precursor solution. We examine the effect of MAI3 on the structural and optoelectronic properties by X-ray diffraction, density functional theory calculations, molecular dynamics simulations, solid-state nuclear magnetic resonance, steady-state, time-resolved photoluminescence (TRPL), and time-resolved terahertz spectroscopy (TRTS). Specifically, TRPL and TRTS show that MAI3 suppresses nonradiative recombination and increases the charge carrier mobility. As a result, the champion device shows a power conversion efficiency (PCE) of 23.46% with a high fill factor of >80%. Furthermore, these devices exhibit enhanced operational stability, with the best device retaining ∼90% of its initial PCE under 1 sun illumination with maximum power point tracking for 350 h.

We report on the preparation of MAPbBr 3 perovskite films of high electronic quality by applying a methylamine (MA) vapor treatment and mitigating surface defects using the amphiphilic molecular passivator, neopentylammonium chloride (NPACl). We find that posttreatment of MAPbBr 3 with methylamine (MA) vapor effectively smooths the surface of the perovskite, eliminating unwanted corrugations and producing phase-pure pinhole free films. The subsequent coating of MAPbBr 3 with NPACl eliminates deleterious surface states that act as electron−hole recombination centers while enhancing the resilience of the perovskite solar cell (PSC) against heat stress and ambient moisture, with solid state NMR demonstrating their atomic-scale interaction. As a result, we achieve an unprecedented V oc of 1.65 V which is a record level for mesoporous single junction PSCs together with a power conversion efficiency (PCE) of over 10% in standard AM 1.5 sunlight. The PSC also retains 91.3% of its initial performance after 1100 h of light soaking under full sunlight and at 60 °C while maintaining the device at maximum power point. In contrast, the pristine PSC maintained only 34% of its initial efficiency under the same aging conditions.