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Organic–inorganic hybrid perovskite materials offer the potential for realization of low-cost and flexible next-generation solar cells fabricated by low-temperature solution processing. Although efficiencies of perovskite solar cells have dramatically improved up to 19% within the past 5 years, there is still considerable room for further improvement in device efficiency and stability through development of novel materials and device architectures. Here we demonstrate that inverted-type perovskite solar cells with pH-neutral and low-temperature solution-processable conjugated polyelectrolyte as the hole transport layer (instead of acidic PEDOT:PSS) exhibit a device efficiency of over 12% and improved device stability in air. As an alternative to PEDOT:PSS, this work is the first report on the use of an organic hole transport material that enables the formation of uniform perovskite films with complete surface coverage and the demonstration of efficient, stable perovskite/fullerene planar heterojunction solar cells.

Ternary structures are demonstrated as a promising approach to increase the efficiency and light harvesting of solar cells. A high power conversion efficiency of 10.2% is achieved for ternary organic solar cells with two efficient polymer donors. The improved performance is attributed to the synergistic effects of enhanced light absorption and charge transport, efficient energy transfer, improved charge generation and morphology.

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AgBiS2 nanocrystals (NCs) have emerged as attractive absorbers in eco-friendly photovoltaics because of their nontoxic components and high absorption coefficient. Native long-chain ligands of AgBiS2 NCs should be replaced with short-chain ligands for their photovoltaics; however, conventional approaches have been performed using solid-state ligand exchange (SSLE), resulting in inhomogeneous NC aggregation, broad bandtail, large trap density, and resultantly low open-circuit voltage (V OC) in devices. Herein, we first report that long-chain ligands of AgBiS2 NCs are replaced with halometallate-based short ligands via solution-phase ligand exchange (SPLE). AgI and BiI3 are used as halometallate sources, and we find that colloidally stable, highly concentrated AgBiS2 NC inks in polar solvents are prepared via SPLE using AgI-based halometallates, enabling one-step-deposition suitable for roll-to-roll process. This leads to higher degree of ligand exchange, sharper bandtail, lower trap density, and resultantly higher V OC in devices compared to conventional SSLE. We also first demonstrate that the photovoltaic performance can be improved by introducing ethanedithiol-exchanged AgBiS2 NCs on SPLE-prepared AgBiS2 NC solids because of favorable band alignment and extended depletion width. Thus, this enables improving device performance up to a power conversion efficiency of 4.08% with the highest V OC of 0.55 V among the AgBiS2 NC photovoltaics reported so far.