This article presents the development of efficient organometal trihalide perovskite planar-heterojunction solar cells on flexible polymer substrates. The perovskite absorber, CH3NH3PbI3-xClx, is processed from solution and sandwiched between organic contacts, achieving power-conversion efficiencies of up to 10% on glass substrates and over 6% on flexible polymer substrates. This work demonstrates the compatibility of perovskite technology with organic photovoltaics, enabling the use of existing knowledge of hybrid interfaces for further device improvements and flexible processing platforms. The perovskite-based solar cells exhibit high power-conversion efficiencies, comparable to or better than existing organic solar cells, and show potential for achieving over 20% efficiencies. The devices are fabricated using low-temperature processing, making them suitable for flexible and deformable substrates. The study also highlights the versatility of the perovskite absorber and its potential for integration into hybrid tandem solar cells. The results indicate that perovskite solar cells can compete with conventional silicon-based solar cells in terms of efficiency and cost. The research also addresses concerns about the toxicity of lead in perovskite materials, noting that lifecycle analysis is needed to assess the environmental impact. The study provides a new approach to design architecture for perovskite-based solar cells, demonstrating their potential for a wide range of substrates, including flexible plastic foils. The work represents a significant step forward in the development of perovskite solar cells, offering a promising alternative to conventional photovoltaic technologies.This article presents the development of efficient organometal trihalide perovskite planar-heterojunction solar cells on flexible polymer substrates. The perovskite absorber, CH3NH3PbI3-xClx, is processed from solution and sandwiched between organic contacts, achieving power-conversion efficiencies of up to 10% on glass substrates and over 6% on flexible polymer substrates. This work demonstrates the compatibility of perovskite technology with organic photovoltaics, enabling the use of existing knowledge of hybrid interfaces for further device improvements and flexible processing platforms. The perovskite-based solar cells exhibit high power-conversion efficiencies, comparable to or better than existing organic solar cells, and show potential for achieving over 20% efficiencies. The devices are fabricated using low-temperature processing, making them suitable for flexible and deformable substrates. The study also highlights the versatility of the perovskite absorber and its potential for integration into hybrid tandem solar cells. The results indicate that perovskite solar cells can compete with conventional silicon-based solar cells in terms of efficiency and cost. The research also addresses concerns about the toxicity of lead in perovskite materials, noting that lifecycle analysis is needed to assess the environmental impact. The study provides a new approach to design architecture for perovskite-based solar cells, demonstrating their potential for a wide range of substrates, including flexible plastic foils. The work represents a significant step forward in the development of perovskite solar cells, offering a promising alternative to conventional photovoltaic technologies.