Interfaces　in　perovskite　and　organic　solar　cells　play　a　central　role　in　advancing　efficiency　and　prolong　device　durability.　They　improve　charge　transport/transfer　from　the　absorber　layer　to　the　collecting　electrodes,　while　also　blocking　the　opposite　charge　carriers,　minimize　voltage　losses　by　suppressing　charge　recombination.　and　may　act　as　buffer/protective　layers　and　nanomorphology　regulators　for　the　absorber　layer.　One　such　interface　is　formed　by　the　hole　transport　layer　(HTL)　and　the　organic/perovskite　absorber.　These　HTLs　typically　consist　of　organic　semiconductors,　which,　although　are　solution　processable　at　low　temperatures　and　allow　perfect　energy-level　alignment　with　the　absorber　layer　and　therefore　efficient　charge　collection,　are　prone　to　degradation　in　ambient　conditions　and　under　continuous　light　exposure.　In　a　quest　for　robust　alternatives,　inorganic　materials　such　as　metal　oxides,　graphene　oxide,　bronzes,　copper　thiocyanate,　and　transition　metal　dichalcogenides　are　actively　investigated.　However,　their　hole　extraction　capability　is　inferior　compared　with　organic　semiconductors　as　they　possess　specific　energetics　leading　to　significant　charge　extraction　barriers　and　moderate　charge　collection.　To　achieve　further　advancements　in　their　hole　transporting　capabilities,　strongly　interconnecting　knowledge　of　their　synthesis,　electronic　properties,　and　device　performance　metrics　is　required.　©　2020　The　Authors.　Solar　RRL　published　by　Wiley-VCH　GmbH